




































1 
 

 



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EPISTEMOLOGY AT A GLANCE. 

 

 

 

 

 

 

 

 

 

 

 

Hyginus Chibuike Ezebuilo 

 

 

 

 

 

 

 

 



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DEDICATION 

In Memory of my Late Mother Mrs Christiana Oyodo Eze (Nee: Nwaezeochebe) 

Buried-23rd April, 2021. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



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ACKNOWLEDGEMENTS 

 

I wish to thank a number of people for their support and contributions for the efforts involved in 

the writing of this book. I wish to thank posthumously in a special way my late Mother, 

Christiana Oyodo Eze for being a source of inspiration and encouragement in my academic 

pursuit. 

I am indebted to Prof. Olatunji A. Oyeshile of University of Ibadan who read the manuscript, 

made corrections and wrote the foreword. And also a doyen in Philosophy, Prof. C.B.Nze, who 

read the work and made his remark. 

To Rev. Fr. Prof. Bonachristus Umeogu, Prof. Ike Odimegwu, Asso. Prof. Charles Nweke and 

Fr. Dr. Gerald Ohaeri,C.S.Sp., whose academic mentorship I enjoy, I am grateful. 

To my Colleagues in the Department of Philosophy, Nnamdi Azikiwe University, Awka and 

Spiritan School of Philosophy, Isienu-Nsukka for making their libraries and providing a 

conducive atmosphere for my academic research. I am very grateful and indebted to you. 

To my Provincial Superior, Fr. Austin Nwosu C.S.Sp Rev. Frs Kenny Udumka, C.S.Sp, Donatus 

Onyeke, C.S.Sp., Mr./Mrs. D.N Iloegbunam and Lady Agatha Iwuoha on whose advise and 

support I ride on, I thank you. 

I owe a lot of gratitude to my friends in Colorado: Kathleen Norwas, Deacon Price and Jeanne 

Hatcher, Janet and Richard Tanski for their financial support. 

Finally, I owe a lot to Vitalis Ogbo for painstakingly reading through the work and organizing 

the typesetting. 

 

Dr. Hyginus Chibuike Ezebuilo 

Department of Philosophy 

Nnamdi Azikiwe University 

Awka. 

 

 

 

 

 

 

 

 

 



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TABLE OF CONTENTS 

CHAPTER ONE: DEFINING EPISTEMOLOGY 

1.1 Introductory Discourse 

1.2 What is Epistemology? 

1.3 Etymology 

CHAPTER TWO: WHAT IS KNOWLEDGE? 

2.1 Different Senses of Knowing 

2.2 A priori and a posteriori knowledge 

2.3 Conditions of Knowledge 

2.3.1 Belief 

2.3.2 Truth 

2.3.3 Justification 

CHAPTER THREE: THEORIES OF TRUTH 

3.1 Classical Theories of Truth, 

3.1.1 Coherence Theories of Truth 

3.1.2 Correspondence Theories of Truth 

3.1.3 The Pragmatist Theory of Truth  

3.4 Semantic Theory of Truth 

3.5 Saul Kripke’s Theory of Truth 

3.6 Karl Popper’s Theory of Truth 

3.7 The Redundancy Theory of Truth 

3.8 Performative Theory of Truth 

3.9 Prosentential Theory of Truth 

3.10 From Truth to Knowledge 

CHAPTER FOUR: IS JUSTIFIED TRUE BELIEF KNOWLEDGE  

4.1 The Gettier Problem 

4.2 Responses to Gettier’s Problem 

4.2.1 No False Premises Response 

4.2.2 Reliabilist Response  

4.2.3 Infallibilist Response 

4.2.4 Indefeasibility Condition 

4.2.5 Tracking Condition 

4.2.6 Knowledge-First Response 

CHAPTER FIVE: THE NATURE OF JUSTIFICATION 

5.1 Internalism and externalism 

5.2 Causal theory and naturalized epistemology 

5.3 The Value Problem (Knowledge v Belief) 

5.4 Virtue Epistemology: A Solution to the Value Problem 

5.5 Cognitive Success vis a vis Epistemic Harms 

5.6 Opinion and Knowledge 



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5.6.1 Metaphor of the Sun 

5.6.2 The Divided Line 

CHAPTER SIX: THEORIES OF JUSTIFICATION 

6.1 Introductory Discourse 

6.2 Deontological and Non-Deontological Justification 

6.3 Deontological Justification 

6.4 Sufficient Likelihood of Justification 

6.5 How is Belief Justified? 

6.5.1 Evidentialism 

6.5.2 Reliabilism 

6.6 Internal vs. External 

6.7 Internalism 

6.7.1 Approaches to Internalism 

6.8 Externalism 

CHAPTER SEVEN: THE STRUCTURE OF JUSTIFICATION 

7.1 Introductory Discourse 

7.2 Foundationalism 

7.2.1 Doxastic Basicality (DB) 

7.2.2 Kinds of Foundationalism 

7.2.3 Privilege Foundationalism 

7.2.4 Experiential Foundationalism 

7.2.5 Privilege vs. Experiential 

7.2.6 Epistemic Basicality (EB) 

7.2.7 The J-Question: EB vs. DB 

7.2.8 Other Possible answers 

7.3 Transfer of Justification 

7.4 Coherentism 

7.4.1 Doxastic Coherentism 

7.4.2 Reliability Coherentism  

7.4.3 Dependence Coherentism .  

7.5 Why Foundationalism? 

7.5.1 The Regress Argument 

7.5.2 Infinitism 

7.6 Why Coherentism? 

7.7 Foundherentism 

CHAPTER EIGHT: SOURCES OF KNOWLEDGE AND JUSTIFICATION 

8.1 Introductory Discourse 

8.2 Perception 

8.3 Introspection 

8.4 Memory 



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8.5 Reason 

8.5.1 A Priori Justification 

8.6 Testimony 

CHAPTER NINE: PHILOSOPHICAL SKEPTICISM 

9.1 Introductory Discourse 

9.2 Ancient Skepticism 

9.3 Kinds of Skepticism 

9.3.1 Extreme/Mild Skepticism 

9.3.2 Pyrrhonism 

9.3.3 Cartesian Skepticism 

9.3.4 General Skepticism 

9.3.5 Selective Skepticism  

9.4 The BIV-Knowledge Closure Argument 

9.5 Responses to the Closure Argument 

9.5.1 Abominable Conjunction  

9.6 Counter BIV  

9.7 The BIV-Justification Under-determination Argument  

9.8 Responses to the Underdetermination Argument  

9.9 The BIV-Knowledge Defeasibility Argument  

9.10 Responses to the Defeasibility Argument  

9.11 The BIV-Epistemic Possibility Argument  

9.12 Responses to the Epistemic Possibility Argument  

CHAPTER TEN: THE HISTORY OF EPISTEMOLOGY: ANCIENT AND MEDIEVAL 

PHILOSOPHIES 

10.1 Ancient Philosophy  

10.1.1 Plato  

10.1.2 Aristotle 

10.1.3 St. Augustine 

10.2 Medieval philosophy 

10.2.1 St. Anselm of Canterbury 

10.2.2 St. Thomas Aquinas 

10.2.3 John Duns Scotus 

10.2.4 William of Ockham 

CHAPTER ELEVEN: THE HISTORY OF EPISTEMOLOGY: MODERN PHILOSOPHY 

11.1 The Rise of Modern Epistemology 

11.2 Faith and reason 

11.3 Epistemology and modern science 

11.4 René Descartes 

11.5 John Locke 

11.6 George Berkeley 

https://www.britannica.com/biography/Plato
https://www.britannica.com/biography/Aristotle
https://www.britannica.com/biography/Saint-Augustine
https://www.britannica.com/biography/Saint-Anselm-of-Canterbury
https://www.britannica.com/biography/Saint-Thomas-Aquinas
https://www.britannica.com/biography/Blessed-John-Duns-Scotus
https://www.britannica.com/biography/William-of-Ockham
https://www.britannica.com/biography/Rene-Descartes
https://www.britannica.com/biography/John-Locke
https://www.britannica.com/biography/George-Berkeley


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11.7 David Hume 

11.7.1 Kinds of Perception 

11.7.2 Relations of ideas and matters of fact 

11.7.3 Cause and effect 

11.7.4 Substance 

11.8 Immanuel Kant 

11.8.1 A Summary of Kant’s Epistemology 

11.9 G.W.F. Hegel 

CHAPTER TWELVE: THE HISTORY OF EPISTEMOLOGY: CONTEMPORARY 

PHILOSOPHY 

12.1 Introductory Discourse  

12.2 Analytic Epistemology 

12.3 Commonsense Philosophy, Logical Positivism, and Naturalized Epistemology 

12.4 Realist Epistemology 

12.5 Continental/Phenomenological Epistemology 

12.5.1 Edmund Husserl. 

12.5.2 Martin Heidegger 

12.5.3 Maurice Merleau-Ponty and Jean-Paul Sartre 

12.6 Later Analytic Epistemology 

CHAPTER THIRTEEN: SOME SCHOOL OF THOUGHTS IN EPISTEMOLOGY 

13.1 Empiricism 

13.2 Rationalism 

13.3 Skepticism 

12.4 Pragmatism 

13.4.1 Charles Peirce 

13.4.2 William James 

13.5 Naturalized Epistemology 

13.6 Feminist Epistemology 

13.7 Relativism 

13.8 Constructivism 

13.9 Idealism 

13.10 Bayesian Epistemology 

13.11 Indian Pramana 

13.12 Social Epistemology 

13.13 Formal Epistemology 

13.14 Metaepistemology 

13.15 Realism 

CHAPTER FOURTEEN: EMPIRICISM 

14.1 What is Empiricism? 

14.2 Various Meanings of Empiricism 

https://www.britannica.com/biography/David-Hume
https://www.britannica.com/topic/relation-logic-and-mathematics
https://www.britannica.com/topic/substance-philosophy
https://www.britannica.com/biography/Immanuel-Kant
https://www.britannica.com/biography/Georg-Wilhelm-Friedrich-Hegel
https://www.britannica.com/topic/philosophy-of-common-sense
https://cdn.britannica.com/38/11138-004-6699034E/Martin-Heidegger.jpg
https://www.britannica.com/biography/Maurice-Merleau-Ponty


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14.2.1 Broader Senses 

14.2.2 Stricter Senses 

12.2.2.1 Absolute Empiricism 

12.2.2.2 Substantive Empiricism 

14.2.2.3 Partial Empiricism  

14.3 Historical Background to Empiricism 

14.3.1 Ancient Philosophy 

14.3.2 Medieval Philosophy 

14.3.3 Modern Philosophy 

14.3.4 Contemporary Philosophy 

14.4 British Empiricism 

14.4.1 John Locke 

14.4.2 George Berkeley 

14.4.3 David Hume 

14.4.4 Phenomenalism 

14.5 Logical Empiricism 

14.6 Criticism and Evaluation 

 CHAPTER FIFTEEN: RATIONALISM 

15.1 What is Rationalism? 

15.2 Expressions of Rationalism 

15.3 History of Rationalism 

15.3.1 Epistemological Rationalism in Ancient Philosophies 

15.3.2 Epistemological Rationalism in Modern Philosophies 

15.3.4 Descartes 

15.3.5 Spinoza  

15.3.6 Leibinz 

15.4 Types of Rationalism 

15.4.1 Ethical Rationalism 

15.4.2 Religious Rationalism 

15.4.2.1 Expansion of Religious Rationalism 

15.4.2.2 Four Waves of Religious Rationalism 

15.5 Status of Rationalism 

15.5.1 Religious 

15.5.2 Ethical 

15.5.3 Metaphysical 

15.6 Challenges to Epistemological Rationalism 

15.7 Major Claims of Rationalism 

15.8 Distinguishing Rationalism from Empiricism  

 

 

https://www.philosophybasics.com/branch_empiricism.html


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                                                                  FOREWORD 

 

        Central to answering the fundamental questions of existence is the epistemological quest to 

know our world. In grappling with numerous problems of human existence such as political, 

social, religious and scientific issues, there is also the problem of meaning. For instance, one 

may ask: When all the contingent problems have been resolved or seem to have been resolved, 

what next? What is the meaning of all these preoccupations after all? While it cannot be said that 

philosophers have answered these questions to the satisfaction of all, at least they have 

contributed adequately to understanding the various dimensions of the problems while the search 

continues. In coming to terms with the problems of existence, our knowledge of the world is very 

crucial. It is the preoccupation of epistemology to grapple with the sources, types, theories and 

skepticism in the domain of knowledge. Epistemology is also a traditional aspect of the 

philosophical enterprise.  

          Again, everyone knows something. In fact, everyone knows some facts about the world 

which are often taken for granted. But our knowledge of the world does not always give us the 

expected result due to certain assumptions which, wittingly or unwittingly, we have taken for 

granted in the knowledge process which behave contrary to expectation. It is on the basis of the 

above that epistemology as a branch of knowledge investigates into how knowledge is possible 

based on certain extant traditional, medieval, modern and contemporary theories of knowledge. 

          Epistemology at a Glance, by Rev. Fr. Dr. Hyginus Chibuike Ezebuilo is one salutary and 

inspiring attempt to contribute to the analysis, application, problem and importance of this core 

branch of philosophy popularly christened epistemology. In achieving his set goals, Rev. Fr. Dr. 

Ezebuilo in the book looks at definition of epistemology, what is knowledge? The nature of 

justification, philosophical skepticism, history of epistemology, rationalism and empiricism 

among others.  

          One may then ask at this juncture: what is new in Rev. Fr. Dr. Ezebuilo’s attempt? 

Afterall, we are used to the problems which mark the regular features of books in epistemology. I 

want to respond to this question based on my thorough but not perfect perusal of the book that 

Dr. Ezebuilo examines the age long problems in epistemology with a view to discussing 

perennial problems in new ways that would impact the knowing process in novel ways that 

would impact the knowing process. We can discern again remarkable simplicity in his book. The 

book is also handy for pedagogical purpose. This implies that it will be a very accessible 

teaching text for students in universities and those who have the quest to have knowledge about 

knowledge for easy application to problems of existence from the theoretical and political 

perspectives. 

   I want to note unequivocally that the central ideas of this book are well discussed with 

appropriate methodologies. One should commend the author for doing a good work. I 



12 
 

recommend the book to all, especially those interested in probing into epistemology as a crucial 

aspect of philosophy and those who are saddled with the task of grappling with the problem of 

existence through the framework of knowledge. 

Olatunji A. Oyeshile, Ph.D, 

Professor of Philosophy, 

University of Ibadan, Nigeria 

and Visiting Researcher/Lecturer 

Institute of Philosophy, 

University of Leiden, 

The Netherlands (2019).     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



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INTRODUCTION 

 The subject matter of Epistemology (Theory of Knowledge) is human knowledge; its nature, 

origin, scope and justification. It probes into the meaning and nature of human knowledge. It 

reflects on issues such as truth and justification which constitute for some scholars, the criteria 

qualifying any belief to count as knowledge. It also examines and attempts to set out the 

possibility of knowledge and foundations of certainty of knowledge. Epistemology is closely 

related to employs data received from Metaphysics in its study of human knowledge. 

Questions concerning the nature and scope of human knowledge have constituted an integral part 

of the discourses of almost all philosophers, right form the Classical Greek Period. In the 

dialogues of Plato (especially Theaetetus, Meno and the Republic) and the writings of Aristotle, 

critical epistemological questions were broached. The later advent of philosophical scepticism 

brought many more epistemological concerns (especially the possibility of human knowledge) 

into the philosophical enterprise. These concerns continued to attract the attention of the 

medieval philosophers, notably the Scholastics. Modern Philosophers from the time of Descartes 

till the contemporary period have without exception struggled with questions about human 

knowledge. In fact, the most outstanding distinction between philosophers by the reckoning of 

many historians of philosophy—the empiricist versus rationalist divide—is largely on 

epistemological grounds arising from question of whether knowledge fundamentally arises from 

sense experience or from the faculty of human reason.  Generally, schools of thought within the 

field of Theory of Knowledge include Empiricism, Rationalism, Scepticism, Feminist 

Epistemology, Naturalized epistemology, Constructivism, Relativism, Epistemic Idealism, 

Epistemic Realism, Metaepistemology and so on.  

Specifically, Epistemology is concerned with propositional knowledge (as against other forms of 

knowledge like knowledge by acquaintance and knowledge of how things are done). 

Propositional knowledge deals primarily with facts properly framed as logical statements. These 

statements can be analytic (solely on the basis of the principle of non-contradiction) or synthetic 

(based on observation of the givens of experience). In Epistemology, distinction is made between 

a priori and a posteriori knowledge. While the former is known independently of experience, the 

latter is apprehended by experience.  



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Additionally, concepts such as belief, truth and justification feature prominently in the 

epistemological discourse. Fundamentally, belief refers to the attitude held by one concerning 

that which one consider true. Belief has been described in many ways by different philosophers 

either as mental states, personal dispositions or interpretative schemes informing one’s actions. 

On its part, truth primarily implies the characteristic of matching up with fact or reality. There 

are many theories of truth, some of which include the Correspondence, Coherence, Sentential, 

Pragmatic and Prosential theories of truth among others. Justification has to do with the rationale 

behind one’s holding on to a reasonable belief. Sources of justification as held by theorists of 

knowledge include reason, experience and testimony of authority. Epistemologists are divided on 

the issue of the conditions of justification. Those who hold these conditions to be outside the 

mental and or psychological states of the subject are called externalists and their posit ion is 

referred to as epistemic externalism. On the other hand, those who hold that these conditions lie 

within the mental and or psychological states of the subject are called internalists and their 

position is referred to as epistemic internalism.  

On the nature of knowledge, there is the question of whether or not justified true belief qualifies 

to be referred to as knowledge and if it not, the next problem would be to determine which one 

has more value. This is the root of the Gettier Problem. On the nature and conditions for 

justification of beliefs, the Virtue Problem arises which culminates in the rise of Virtue 

Epistemology which goes beyond the knowledge facts themselves and proceeds with the 

evaluation of the intellectual virtues of the subjects.  

The Regress Problem arises, considering the question of the logical foundations of human 

knowledge. Responses to this problem gave rise to different paradigms of thought—

Coherentism, Foundationalism, Infinitism and Foundherentism. Finally, the question arises 

whether or not knowledge is even possible, given the difficulty in satisfying the condition of 

epistemic certainty which is at the heart of the definition of knowledge itself. This gave rise to 

the problem of Philosophic Skepticism which is almost as old as Philosophy itself and remains an 

intractable epistemological problem. Arguments raised against skepticism include the Polar 

Argument and the Paradigm Case Argument.  

 

 



15 
 

CHAPTER ONE 

DEFINING EPISTEMOLOGY 

1.1 Introductory Discourse 

Epistemology, as a distinct field of inquiry, predates the introduction of the term into the lexicon 

of philosophy. John Locke, for instance, described his efforts in Essay Concerning Human 

Understanding (1689) as an inquiry “into the original, certainty, and extent of human knowledge, 

together with the grounds and degrees of belief, opinion, and assent.”1 

 

René Descartes, who is often credited as the father of modern philosophy, was often preoccupied 

with epistemological questions in his work. Almost every major historical philosopher has 

considered questions about what we know and how we know it. Among the Ancient Greek 

philosophers, Plato distinguished between inquiry regarding what we know and inquiry 

regarding what exists. A number of important epistemological concerns also appeared in the 

works of Aristotle.  

 

During the subsequent Hellenistic period, philosophical schools began to appear which had a 

greater focus on epistemological questions, often in the form of philosophical skepticism. For 

instance, the Pyrrhonian skepticism of Pyrrho and Sextus Empiricus held 

that eudaimonia (flourishing, happiness, or “the good life”) could be attained through the 

application of epoché (suspension of judgment) regarding all non-evident matters.2 Pyrrhonism 

was particularly concerned with undermining the 

epistemological dogmas of Stoicism and Epicureanism. The other major school of Hellenistic 

skepticism was Academic skepticism, most notably defended by Carneades and Arcesilaus, 

which predominated in the Platonic Academy for almost two centuries.3 They were specialized 

in refutation without propagating any positive doctrine of their own. 

After the ancient philosophical era but before the modern philosophical era, a number 

of Medieval philosophers also engaged with epistemological questions at length. Most notable 

among the Medievals for their contributions to epistemology were Thomas Aquinas, John Duns 

Scotus, and William of Ockham. In the Islamic epistemology Islamic Golden Age which was 

booming prior to the Age of Enlightenment in Europe. One of the most prominent and influential 

philosophers, theologians, jurists, logicians and mystics Abu Hamid Al-Ghazali was seeking to 

know what we can be certain about: what is true knowledge and not just opinion? To accomplish 

this goal, he would first consider what kinds of things we can know. This involves a study of 

epistemology, the theory of knowledge.4 

                                                             
1 John Locke, “Introduction,” An Essay Concerning Human Understanding (Oxford: Oxford University Press, 1975). 
2 Paul K. Moser, The Oxford Handbook of Epistemology (Oxford: oxford University Press, 2002), 101. 
3 Ibid. 
4 Ibid.,102. 

https://en.wikipedia.org/wiki/John_Locke
https://en.wikipedia.org/wiki/An_Essay_Concerning_Human_Understanding
https://en.wikipedia.org/wiki/An_Essay_Concerning_Human_Understanding
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Ancient_Greek_philosophy
https://en.wikipedia.org/wiki/Ancient_Greek_philosophy
https://en.wikipedia.org/wiki/Plato
https://en.wikipedia.org/wiki/Aristotle
https://en.wikipedia.org/wiki/Hellenistic_philosophy
https://en.wikipedia.org/wiki/Philosophical_skepticism
https://en.wikipedia.org/wiki/Pyrrhonism
https://en.wikipedia.org/wiki/Pyrrho
https://en.wikipedia.org/wiki/Sextus_Empiricus
https://en.wikipedia.org/wiki/Eudaimonia
https://en.wikipedia.org/wiki/Epoch%C3%A9
https://en.wikipedia.org/wiki/Dogma
https://en.wikipedia.org/wiki/Stoicism
https://en.wikipedia.org/wiki/Epicureanism
https://en.wikipedia.org/wiki/Academic_skepticism
https://en.wikipedia.org/wiki/Carneades
https://en.wikipedia.org/wiki/Arcesilaus
https://en.wikipedia.org/wiki/Platonic_Academy
https://en.wikipedia.org/wiki/Medieval_philosophy
https://en.wikipedia.org/wiki/Thomas_Aquinas
https://en.wikipedia.org/wiki/John_Duns_Scotus
https://en.wikipedia.org/wiki/John_Duns_Scotus
https://en.wikipedia.org/wiki/William_of_Ockham
https://en.wikipedia.org/wiki/Islamic_Golden_Age
https://en.wikipedia.org/wiki/Al-Ghazali
https://archive.org/details/in.ernet.dli.2015.223061


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Epistemology largely came to the fore in philosophy during the early modern period, which 

historians of philosophy traditionally divide up into a dispute 

between empiricists (including Francis Bacon, John Locke, David Hume, and George Berkeley) 

and rationalists (including René Descartes, Baruch Spinoza, and Gottfried Leibniz). The debate 

between them has often been framed using the question of whether knowledge comes primarily 

from sensory experience (empiricism), or whether a significant portion of our knowledge is 

derived entirely from our faculty of reason (rationalism). According to some scholars, this 

dispute was resolved in the late 18th century by Immanuel Kant, whose transcendental 

idealism famously made room for the view that “though all our knowledge begins with 

experience, it by no means follows that all [knowledge] arises out of experience.”5 

There are a number of different methods that contemporary scholars use when trying to 

understand the relationship between past epistemology and contemporary epistemology. One of 

the most contentious questions is this: Should we assume that the problems of epistemology are 

perennial, and that trying to reconstruct and evaluate Plato’s or Hume’s or Kant’s arguments is 

meaningful for current debates, too?.6 Similarly, there is also a question of whether 

contemporary philosophers should aim to rationally reconstruct and evaluate historical views in 

epistemology, or to merely describe them.7 Barry Stroud claims that doing epistemology 

competently requires the historical study of past attempts to find philosophical understanding of 

the nature and scope of human knowledge.8 He argues that since inquiry may progress over time, 

we may not realize how different the questions that contemporary epistemologists ask, are 

questions asked at various different points in the history of philosophy. 

 

1.2 What is Epistemology? 

The term “epistemology” comes from the Greek words episteme and logos. While episteme can 

be translated as knowledge, understanding or acquaintance, logos can be translated as account, 

argument or reason. Each of these different translations captures some facet of the meaning of 

these Greek terms as well as a different facet of epistemology itself. 

In different parts of its history, different facets of epistemology have attracted attention.9 Plato’s 

epistemology is an attempt to understand what it is to know, and how knowledge (unlike mere 

true opinion) is attributed to the knower. Aristotle’s epistemology delimits what we can know 

and how we can know. Similarly, John Locke’s epistemology is an attempt to understand the 

operations of human understanding. Immanuel Kant’s epistemology attempts to understand the 

                                                             
5 Thomas Sturm, “Historical Epistemology or History of Epistemology? The Case of the Relation Between 
Perception and Judgment,” Erkenntnis 75(3), 304. 
6John Bengson and Marc A. Moffett (eds.), Essays on Knowledge, Mind, and Action (New York: Oxford University 
Press, 2011), 14-15. 
7 Ibid. 
8see Mathew Benton, “Epistemology Personalized,” The Philosophical Quarterly. 67(269), (2011), 813. 
9 M. steup and Ram Nata, “Epistemology,” The Stanford Encyclopedia of Philosophy (2020), Edward N. Zalta (ed.). 
uRL = https://plato.stanford.edu/archives/fall2020/. 

https://en.wikipedia.org/wiki/Modern_philosophy
https://en.wikipedia.org/wiki/Empiricism
https://en.wikipedia.org/wiki/Francis_Bacon
https://en.wikipedia.org/wiki/John_Locke
https://en.wikipedia.org/wiki/David_Hume
https://en.wikipedia.org/wiki/George_Berkeley
https://en.wikipedia.org/wiki/Rationalism
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Baruch_Spinoza
https://en.wikipedia.org/wiki/Gottfried_Leibniz
https://en.wikipedia.org/wiki/Experience
https://en.wikipedia.org/wiki/Reason
https://en.wikipedia.org/wiki/Immanuel_Kant
https://en.wikipedia.org/wiki/Transcendental_idealism
https://en.wikipedia.org/wiki/Transcendental_idealism
https://en.wikipedia.org/wiki/Barry_Stroud
https://philpapers.org/rec/BENEP-3


17 
 

conditions of the possibility of human understanding, while that of Russell is an attempt to 

understand how modern science could be justified by appeal to sensory experience. Much recent 

work in epistemology is an attempt to understanding the justification for our knowledge claims. 

This is sometimes affected by interest…..In any case epistemology tries to understand our 

cognitive success or cognitive failure. 

Epistemology is the branch of philosophy concerned with knowledge. Epistemologists study the 

nature, origin, and scope of knowledge, epistemic justification, the rationality of belief, and 

various related issues. Epistemology is considered a major subfield of philosophy, along with 

other major subfields such as ethics, logic, and metaphysics.  

Problems in epistemology are generally clustered around four core areas:  

1. The philosophical analysis of the nature of knowledge and the conditions required for a 

belief to constitute knowledge, such as truth and justification. 

2. Potential sources of knowledge and justified belief, such as perception, reason, memory, 

and testimony. 

3. The structure of a body of knowledge or justified belief, including whether all justified 

beliefs must be derived from justified foundational beliefs or whether justification 

requires only a coherent set of beliefs. 

4. Philosophical skepticism, which questions the possibility of knowledge, and related 

problems, such as whether skepticism poses a threat to our ordinary knowledge claims 

and whether it is possible to refute skeptical arguments. 

In all these, epistemology aims to answer questions such as “What do we know?”, “What does it 

mean to say that we know something?”, “What makes justified beliefs justified?”, and “How do 

we know that we know?” 

1.3 Etymology 

The word epistemology is derived from the ancient Greek epistēmē, meaning “knowledge”, and 

the suffix -logia, meaning “logical discourse” (derived from the Greek word logos meaning 

“discourse”).10 The appearance of the word in English was predated by the German 

term Wissenschaftslehre (literally, theory of science), which was introduced by 

philosophers Johann Fichte and Bernard Bolzano in the late 18th century. The word 

“epistemology” first appeared in 1847, in a review in New York’s Eclectic Magazine. It was first 

used as a translation of the word Wissenschaftslehre as it appears in a philosophical novel by 

German author Jean Paul. The title of one of the principal works of Fichte is 

‘Wissenschaftslehre,’ which is now rendered epistemology.11 

                                                             
10“Epistemology,” Oxford English Dictionary (3rd ed.) (Oxford: Oxford University Press. 2014). 
11Anonymous, “Jean-Paul Frederich Richter,” The Eclectic Magazine of Foreign Literature, Science and Art. 12, 
(1847), 317. 

https://en.wikipedia.org/wiki/Outline_of_philosophy
https://en.wikipedia.org/wiki/Knowledge
https://en.wikipedia.org/wiki/Justification_(epistemology)
https://en.wikipedia.org/wiki/Reason
https://en.wikipedia.org/wiki/Belief
https://en.wikipedia.org/wiki/Ethics
https://en.wikipedia.org/wiki/Logic
https://en.wikipedia.org/wiki/Metaphysics
https://en.wikipedia.org/wiki/Philosophical_analysis
https://en.wikipedia.org/wiki/Truth
https://en.wikipedia.org/wiki/Justification_(epistemology)
https://en.wikipedia.org/wiki/Perception
https://en.wikipedia.org/wiki/Reason
https://en.wikipedia.org/wiki/Memory
https://en.wikipedia.org/wiki/Testimony#Philosophy
https://en.wikipedia.org/wiki/Foundationalism
https://en.wikipedia.org/wiki/Coherentism
https://en.wikipedia.org/wiki/Philosophical_skepticism
https://en.wikipedia.org/wiki/Episteme
https://en.wikipedia.org/wiki/Discourse
https://en.wikipedia.org/wiki/Johann_Fichte
https://en.wikipedia.org/wiki/Bernard_Bolzano
https://en.wikipedia.org/wiki/Jean_Paul


18 
 

The word "epistemology" was properly introduced into Anglophone philosophical literature by 

Scottish philosopher James Frederick Ferrier in 1854, who used it in his Institutes of 

Metaphysics: 

This section of the science is properly termed the 

Epistemology—the doctrine or theory of knowing, just as 

ontology is the science of being... It answer rs the general 

question, ‘What is knowing and the known?’—or more 

shortly, ‘What is knowledge?’ 

It is important to note that the French term épistémologie is used with a different and far 

narrower meaning than the English term “epistemology”, being used by French philosophers to 

refer solely to philosophy of science. For instance, Émile Meyerson opened his Identity and 

Reality, written in 1908, with the remark that the word is becoming current as equivalent to “the 

philosophy of the sciences.”12 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                             
12 Cf. Wal Suchting, “Epistemology,” Historical Materialism, (2018), 331. 

https://en.wikipedia.org/wiki/James_Frederick_Ferrier
https://en.wikipedia.org/wiki/Philosophy_of_science
https://en.wikipedia.org/wiki/%C3%89mile_Meyerson


19 
 

CHAPTER TWO 

WHAT IS KNOWLEDGE? 

2.1 Different Senses of Knowing 

Before we can start to explore the arguments developed by different philosophers in the search 

for knowledge, we first need to understand what philosophers mean by ’knowledge’. 

Traditionally, there are three different types of knowledge:  practical knowledge: knowledge that 

is skills-based, e.g. being able to drive or use a computer knowledge by acquaintance: knowledge 

that doesn’t involve facts but familiarity with someone or an objects, e.g. I know my mother, I 

know what an apple looks like factual knowledge: knowledge based on fact, e.g. I know that the 

sun rises every morning – I know it is true. Philosophers are mostly interested in factual 

knowledge because they are trying to understand how we can achieve truth about the world. 

One of the first philosophers to attempt a definition of knowledge was the Ancient Greek 

philosopher, Plato. One of Plato’s main concerns was to distinguish knowledge from belief. He 

gave the example of two guides, one who knows the road to a certain destination, and the other 

who just uses guesswork. Both guides arrive at their destination but which one is more reliable? 

Most people would argue that the guide who has expertise is more reliable. This is why Plato 

argues that true belief gives us knowledge of the world only by coincidence. It is never really 

certain and could change at any time. For example, I may believe in aliens and aliens may 

actually exist, but if I cannot give an adequate reason for my claim. I can’t really call it 

knowledge. Plato argues that for a factual claim to be knowledge, it has to be a belief which is 

true and justified. His definition of knowledge is therefore that it is must be a justified true belief.  

Almost every debate in epistemology is in some way related to knowledge. Most generally, 

“knowledge” is a familiarity, awareness, or understanding of someone or something, which 

might include facts (propositional knowledge), skills (procedural or how-to knowledge), or 

objects (acquaintance knowledge). Philosophers tend to draw an important distinction between 

three different senses of knowing something: “knowing that” (knowing the truth of propositions), 

“knowing how” (understanding how to perform certain actions), and “knowing by acquaintance” 

(directly perceiving an object, being familiar with it, or otherwise coming into contact with 

it). Epistemology is primarily concerned with the first of these forms of knowledge, 

propositional knowledge. 

All three senses of knowing can be seen in our ordinary use of the word. In mathematics, you can 

know that 2 + 2 = 4, but there is also knowing how to add two numbers, and knowing 

a person (e.g., knowing other persons, or knowing oneself), place (e.g., one's 

hometown), thing (e.g., cars), or activity (e.g., addition).13 While these distinctions are not 

explicit in English, they are explicitly made in other languages, including French, Portuguese, 

Spanish, Romanian, German and Dutch (although some languages related to English have been 

                                                             
13 “Formal Representations of Belief” Stanford Encyclopedia of Philosophy, Retrieved October 24, 2021.   

https://en.wikipedia.org/wiki/Knowledge
https://en.wikipedia.org/wiki/Propositional_knowledge
https://en.wikipedia.org/wiki/Procedural_knowledge
https://en.wikipedia.org/wiki/Knowledge_by_acquaintance
https://en.wikipedia.org/wiki/Propositional_knowledge
https://en.wikipedia.org/wiki/Procedural_knowledge
https://en.wikipedia.org/wiki/Knowledge_by_acquaintance
https://plato.stanford.edu/entries/formal-belief/


20 
 

said to retain these verbs, such as Scots). The theoretical interpretation and significance of these 

linguistic issues remains controversial. 

In his paper book Problems of Philosophy, Bertrand Russell brought a great deal of attention to 

the distinction between “knowledge by description” and “knowledge by acquaintance.”14 Gilbert 

Ryle is similarly credited with bringing more attention to the distinction between knowing how 

and knowing that in The Concept of Mind.15 In Personal Knowledge, Michael Polanyi argues for 

the epistemological relevance of knowledge how and knowledge that; using the example of the 

act of balance involved in riding a bicycle, he suggests that the theoretical knowledge of the 

physics involved in maintaining a state of balance cannot substitute for the practical knowledge 

of how to ride, and that it is important to understand how both are established and grounded.16 

This position is essentially Ryle’s, who argued that a failure to acknowledge the distinction 

between “knowledge that” and “knowledge how” leads to infinite regress.17 

2.2 A priori and a posteriori knowledge 

One of the most important distinctions in epistemology is between what can be known a 

priori (independently of experience) and what can be known a posteriori (through experience). 

The terms originate from the Analytic methods of Aristotle’s Organon, and may be roughly 

defined as follows:18 

 A priori knowledge is knowledge that is known independently of experience (that is, it is 

non-empirical, or arrived at before experience, usually by reason). It will henceforth be 

acquired through anything that is independent from experience. 

 A posteriori knowledge is knowledge that is known by experience (that is, it is empirical, 

or arrived at through experience). 

Views that emphasize the importance of a priori knowledge are generally classified 

as rationalist. Views that emphasize the importance of a posteriori knowledge are generally 

classified as empiricist. 

 

2.3 Conditions of Knowledge  

The traditional definition of knowledge as handed down from Plato is: justified true belief.  

2.3.1 Belief 

                                                             
14 B. Russell, Problem of Philosophy, https://www.sparknotes.com/russell/problem-of-philosophy/ 
15 Gilbert Ryle, The Concept of Mind, https://www.britannica.com/topic/concept-of-mind/ 
16Michael Polanyi, Personal Knowledge., https://www.giffordlectures.org/personal-knowledge. 
17 Gilbert Ryle, The Concept of Mind. 
18 Cf. Benardete Seth, The Being of the Beautiful (Chicago: The University of Chicago Press, 1984),169. 

https://en.wikipedia.org/wiki/Scots_language
https://en.wikipedia.org/wiki/Bertrand_Russell
https://en.wikipedia.org/wiki/Descriptive_knowledge
https://en.wikipedia.org/wiki/Knowledge_by_acquaintance#Bertrand_Russell
https://en.wikipedia.org/wiki/Gilbert_Ryle
https://en.wikipedia.org/wiki/Gilbert_Ryle
https://en.wikipedia.org/wiki/The_Concept_of_Mind
https://en.wikipedia.org/wiki/Michael_Polanyi
https://en.wikipedia.org/wiki/Infinite_regress
https://en.wikipedia.org/wiki/Organon
https://en.wikipedia.org/wiki/A_priori_and_a_posteriori
https://en.wikipedia.org/wiki/A_priori_and_a_posteriori
https://en.wikipedia.org/wiki/Rationalist
https://en.wikipedia.org/wiki/Empiricist
https://en.wikipedia.org/wiki/Michael_Polanyi


21 
 

One of the core concepts in epistemology is belief. A belief is an attitude that a person holds 

regarding anything that he take, to be true.19 For instance, to believe that snow is white is 

comparable to accepting the truth of the proposition “snow is white”. Beliefs can 

be occurrent (example, a person actively thinking “snow is white”), or they can 

be dispositional (example, a person who if asked about the color of snow would assert “snow is 

white”). While there is no universal agreement about the nature of belief, most contemporary 

philosophers hold the view that a disposition to express belief B qualifies as holding the 

belief B.20 There are various different ways that contemporary philosophers have tried to 

describe beliefs, including as representations of ways that the world could be, as dispositions to 

act as if certain things are true, as interpretive schemes for making sense of someone’s actions, or 

as mental states that fill a particular function.21 

Some have also attempted to offer significant revisions to our notion of belief, 

including eliminativists about belief who argue that there is no phenomenon in the natural world 

which corresponds to our folk psychological concept of belief; and formal epistemologists who 

aim to replace our bivalent notion of belief (either I have a belief or I don’t have a belief) with 

the more permissive, probabilistic notion of credence (there is an entire spectrum of degrees of 

belief, not a simple dichotomy between belief and non-belief.22 

While belief plays a significant role in epistemological debates surrounding knowledge and 

justification, it also has many other philosophical debates in its own right. Notable debates 

include: What is the rational way to revise one's beliefs when presented with various sorts of 

evidence?; Is the content of our beliefs entirely determined by our mental states, or do the 

relevant facts have any bearing on our beliefs (example, if I believe that I am holding a glass of 

water, is the non-mental fact that water is H2O part of the content of that belief)?;  and Must it be 

possible for a belief to be expressible in language, or are there non-linguistic beliefs? 

2.3.2 Truth 

Truth is the property or state of being in accordance with facts or reality.23 On most views, truth 

is the correspondence of language or thought to a mind-independent world. This is called 

the correspondence theory of truth. Among philosophers who think that it is possible to analyze 

the conditions necessary for knowledge, virtually all of them accept that truth is such a condition. 

There is much less agreement about the extent to which a knower must know why something is 

true in order to know. On such views, something being known implies that it is true. However, 

this should not be confused for the more contentious view that one must know that one knows in 

order to know.  

                                                             
19Edmund L. Gettier, “Is Justified True Belief Knowledge?” Analysis, Vol. 23, (1963), 121–123. 
20 Ibid. 
21“The Analysis of Knowledge,” Stanford Encyclopedia of Philosophy, Retrieved October 27, 2021. 
22 Ibid. 
23 Rene Descartes, The Philosophical Writings of Rene Descartes Vol. I. (Cambridge University Press, 1985), 171. 

https://en.wikipedia.org/wiki/Proposition
https://en.wikipedia.org/wiki/Eliminativism
https://en.wikipedia.org/wiki/Folk_psychology
https://en.wikipedia.org/wiki/Formal_epistemology
https://en.wikipedia.org/wiki/Truth
https://en.wikipedia.org/wiki/Correspondence_theory_of_truth
http://www.ditext.com/gettier/gettier.html
https://en.wikipedia.org/wiki/Analysis_(journal)
https://plato.stanford.edu/entries/knowledge-analysis/


22 
 

Epistemologists disagree about whether belief is the only truth-bearer. Other common 

suggestions for things that can bear the property of being true 

include propositions, sentences, thoughts, utterances, and judgments. Plato argues that belief is 

the most commonly invoked truth-bearer. Many of the debates regarding truth are at the 

crossroads of epistemology and logic. Some contemporary debates regarding truth include: How 

do we define truth? Is it even possible to give an informative definition of truth? What things are 

truth-bearers and are therefore capable of being true or false? Are truth and falsity bivalent, or 

are there other truth values? What are the criteria of truth that allow us to identify it and to 

distinguish it from falsity? What role does truth play in constituting knowledge? And is 

truth absolute, or is it merely relative to one’s perspective? 

2.3.3 Justification 

As the term “justification” is used in epistemology, a belief is justified if one has good reason for 

holding it. Loosely speaking, justification is the reason for which someone holds a rationally 

admissible belief, on the assumption that it is a good reason for holding it. Sources of 

justification might include perceptual experience (the evidence of the senses), reason, and 

authoritative testimony, among others. Importantly however, a belief being justified 

does not guarantee that the belief is true, since a person could be justified in forming beliefs 

based on very convincing evidence that was nonetheless deceiving. 

In Plato’s Theaetetus, Socrates considers a number of theories as to what knowledge is, first 

excluding merely true belief as an adequate account. For example, an ill person with no medical 

training, but with a generally optimistic attitude, might believe that he will recover from his 

illness quickly. Nevertheless, even if this belief turned out to be true, the patient would not 

have known that he would get well since his belief lacked justification. The last account that 

Plato considers is that knowledge is true belief with an account24 that explains or defines it in 

some way. According to Edmund Gettier, the view that Plato is describing here is that 

knowledge is justified true belief. The truth of this view would entail that in order to know that a 

given proposition is true, one must not only believe the relevant true proposition, but must also 

have a good reason for doing so.25 One implication of this would be that no one would gain 

knowledge just by believing something that happened to be true.26 

 

 

 

 

 

                                                             
24 Ibid. 
25Edmund L. Gettier, “Is Justified True Belief Knowledge?”  
26 Ibid. 

https://en.wikipedia.org/wiki/Truth-bearer
https://en.wikipedia.org/wiki/Propositions
https://en.wikipedia.org/wiki/Sentence_(mathematical_logic)
https://en.wikipedia.org/wiki/Thought
https://en.wikipedia.org/wiki/Utterance
https://en.wikipedia.org/wiki/Judgment
https://en.wikipedia.org/wiki/Logic
https://en.wikipedia.org/wiki/Principle_of_bivalence
https://en.wikipedia.org/wiki/Criteria_of_truth
https://en.wikipedia.org/wiki/Knowledge
https://en.wikipedia.org/wiki/Absolute_(philosophy)
https://en.wikipedia.org/wiki/Knowledge_relativity
https://en.wikipedia.org/wiki/Perception
https://en.wikipedia.org/wiki/Reason
https://en.wikipedia.org/wiki/Testimony
https://en.wikipedia.org/wiki/Plato
https://en.wikipedia.org/wiki/Theaetetus_(dialogue)
https://en.wikipedia.org/wiki/Socrates
https://en.wikipedia.org/wiki/Edmund_Gettier
http://www.ditext.com/gettier/gettier.html


23 
 

CHAPTER THREE 

THEORIES OF TRUTH 

In this chapter, I shall briefly sketch three classical and other major kinds of theories of truth 

which have been proposed, and attempt to indicate how they relate to each other. 

3.1 Coherence Theories of Truth 

Coherence theories take truth to consist in relations of coherence among a set of beliefs. Simply 

put, coherence theory of truth holds that truth consists in coherence; the test of the truth of all 

statements derives from their relations with other statements. The test for truth consists of 

relations among beliefs themselves. Our search for knowledge thus requires a consistence 

readjustment of beliefs, the aim of which is to achieve coherence. For instance, if in a certain 

village inter-family marriage is not permitted, then it is not plausible to believe that A is the 

husband of B when it has been established that A and B are siblings. Also, such statements as 

“twice two is half of eight” or “what is known cannot be unknown” are true in virtue of the 

meanings of the words that express them. It is because the meanings of the words are internally 

related as they are (i.e. coherence) that these statements are true. According to the coherence 

theory of justification, also known as coherentism, a belief is justified, or justifiably held, only if 

it coheres with a set of beliefs already known to be true and justified. However, there is a 

refutation on this theory, which posits that, to insist that a judgment is true because of its 

coherence and consistency with a reality that is accepted as true, could lead to a dangerous 

circularity. An example is, when there are false statements, each claiming to be true for reasons 

of coherence.  In this way, the theory does not distinguish between a coherent or consistent truth 

and a consistent error. 

3.2 Correspondence Theories of Truth 

Correspondence theories take the truth of a proposition to consist, not in its relation to other 

propositions, but in its relation to the world, its correspondence to reality or to the facts. During 

their “logical atomist” periods, both Russell and Wittgenstein offered definitions of truth as the 

correspondence of a proposition to facts. The question however is, how do we tell whether or not 

a sentence corresponds to the fact? To tackle the problem Carnap argues that statements 

reporting immediate perceptual experience are incorrigible, that is to say, we can directly verify 

that they correspond to the facts. For instance, the statement that, it is raining, can only be true if 

it can be verified that it is actually raining. If this is done, then one can say that the statement 

corresponds to the fact, and as such, the statement is true. In other words, the correspondence 

theory of truth states that the truth or falsity of a statement is determined only by how it relates to 

the world and whether it accurately describes (i.e., corresponds with) that world. There is a 

loophole in this theory. As we have seen above, the theory compares ideas with reality. But, can 

ideas be compared with reality? Since we know only our own experience, how can we get 

outside our ideas to get to reality as it is in itself? 

 



24 
 

3.3 The Pragmatist Theory of Truth  

The pragmatist theory developed in the works of Peirce, Dewey, and James has affinities with 

both coherence and correspondence theories, allowing that the truth of a belief derives from its 

correspondence with reality, but stressing also that it is manifested by the belief’s survival of test 

by experience, and its coherence with other beliefs. Only a truth of this kind is workable. 

According to the pragmatic maxim, the meaning of a concept is to be given by reference to the 

practical or experimental consequences of its application. As James puts it,27 there can be no 

difference that makes no difference. Hence, the pragmatic approach to truth is to ask what 

difference it makes whether a belief is true. For instance, would it make any difference to believe 

that God exists? Would the application of such a belief work out for the good of the society? If 

the answer is yes, then the statement that God exists is true, otherwise it is false. The problem 

associated with this theory is that it has some relativist tendencies.  

3.4 Semantic Theory of Truth 

Aristotle has observed that “to say of what is that it is not, or of what is not that it is, is false, 

while to say of what is that it is, or of what is not that it is not, is true.”28 In proposing his 

semantic theory of truth, Tarski aims to explicate the sense of “true” which the above dictum 

captures. Truth, in Tarski’s account, is defined in terms of the semantic relation of satisfaction, a 

relation between open sentences (e.g. x is greater than y) and non-linguistic objects (e.g. the 

numbers 6 and 5). 

3.5 Saul Kripke’s Theory of Truth 

The truth theory recently proposed by Kripke (1975) is a variant of Tarski’s account, modified 

essentially to cope in a more sophisticated way with semantic paradoxes. His theory builds on 

valued interpretation of language. For instance, he avers that sentences many be neither true nor 

false (N) as well as true (T) or false (F).29 It is a formal theory of truth, believed to be alternative 

to Tarski’s ‘orthodox’ theory, based on truth-value gaps. The theory is proposed as a fairly 

plausible model for natural language and as one which allows rigorous definitions to be given for 

various intuitive concepts, such as semantic paradoxes. A semantic paradox is a seemingly 

contradictory or absurd statement that expresses a possible truth; it can also mean a self-

contradictory and false proposition. The liar paradox is one of the simplest yet most famous 

example of paradoxes out there. The statement “this statement is a lie” or “this statement is 

false” is a paradox because if that statement is indeed a lie, then it would be saying a truth. 

3.6 Karl Popper’s Theory of Truth 

Popper’s account of truth and his theory of verisimilitude or nearness to the truth is also based 

upon Tarski’s theory, which Popper regards as supplying a more precise version of traditional 

                                                             
27 Tarski, Alfred. “The Semantic Conception of Truth and the Foundations of Semantics.” In Philosophy and 
Phenomenological Research, 4, 1944. 
28 Ibid. 
29 Kripke, Saul. Outline of a Theory of Truth. Journal of Philosophy, 72(1), 1975,690-716. 



25 
 

correspondence theories. Popper is one of the most prominent philosophers of science. But his 

falsificationist proposal differs from the verifiability criterion in some important ways.30 First, 

Popper does not hold that non-scientific claims are meaningless. Instead, he argues that such a 

unfalsifiable claims can often serve important roles in both scientific and philosophical contexts, 

even if we are incapable of asserting their truth or falsity. Second, while Popper is a realist who 

holds that scientific theories aim at the truth, he does not think that empirical evidence can ever 

provide us grounds for believing that a theory is either true or likely to be true.31 In this sense, 

Popper is a fallibilist who holds that while the particular unfalsified theory we have adopted 

might be true, we could never know this to be the case. For this same reason, Popper holds that it 

is impossible to provide justification for one’s belief that a particular scientific theory is true. 

Finally, where others see science progressing by confirming the truth of various particular 

claims, Popper describes science as progressing on an evolutionary model, with observations 

selecting against unfit theories by falsifying them. 

In philosophy, verisimilitude (or truthlikeness) is the notion that some propositions are closer to 

being true than other propositions. The problem of verisimilitude is the problem of articulating 

what it takes for one false theory to be closer to the truth than another false theory.32 This 

problem was central to the philosophy of Karl Popper, largely because Popper was among the 

first to affirm that truth is the aim of scientific inquiry while acknowledging that most of the 

greatest scientific theories in the history of science are, strictly speaking, false.33 If this long 

string of purportedly false theories is to constitute progress with respect to the goal of truth, then 

it must be at least possible for one false theory to be closer to the truth than others. 

3.7 The Redundancy Theory of Truth 

The redundancy theory of truth, offered by Ramsey (1927) claims that “true” is redundant, for to 

say that it is true that p is equivalent to saying that p. Evidently, this account has some affinities 

with Aristotle’s dictum, and consequently with some aspects of Tarski’s theory. According to 

this theory, asserting that a statement is true is completely equivalent to asserting the statement 

itself. For example, asserting the sentence “snow is white is true” is the same as asserting the 

sentence “snow is white.” Frege expressed the idea this way: 

It is worthy of notice that the sentence “I smell the scent of 

violets” has the same content as the sentence “It is true that 

I smell the scent of violets.” So it seems, then, that nothing 

                                                             
30H.C. Ezebuilo, “Popper’s Piecemeal Engineering and Social Reform in Africa.” Unpublished Thesis Submitted to 
Nnamdi Azikiwe University Awka, 2017.  
31 Ibid. 
32 “Truthlikeness,” Stanford Encyclopedia of Philosophy. Retrieved October 22, 2022. 
33 Pavel Tichy. On Poper’s Definitions of Verisimilitude. The British Journal for the Philosophy of Science. (Oxford 
University Press, 1974), 25(2):155-160. 



26 
 

is added to the thought by my ascribing to it the property of 

truth.34 

When we assert a proposition explicitly, such as when we say “I smell the scent of violets,” then 

saying “It is true that I smell the scent of violets” would be redundant; it would add nothing 

because the two have the same meaning. In other words, the two are necessarily equivalent. 

3.8 Performative Theory of Truth 

Peter Strawson formulated a performative theory of truth in the 1950s. Like Ramsey, Strawson 

believed that there is no separate problem of truth apart from determining the semantic contents 

(or facts of the world) which gives the words and sentences of language the meanings that they 

have.35 The performative theory of truth argues that ascribing truth to a proposition is not really 

characterizing the proposition itself, nor is it saying something redundant. Rather, it is telling us 

something about the speaker’s intentions. Through the speaker’s praising, accepting, conceding, 

agreeing with, or endorsing of the proposition, he or she is guaranteeing our adoption (our belief 

in) the proposition. Instead of saying, “It is true snow is white,” one could substitute, “I embrace 

the claim that snow is white.” The key idea is that saying of some proposition, P, that it is true is 

to say in a disguised fashion, “I commend P to you,” or “I endorse P,” or something of the sort. 

In this case, you are performing the action of giving your listener license or guarantee to belief 

the proposition (and to act upon the belief). 

3.9 Prosentential Theory of Truth 

The prosentential theory of truth suggests that the grammatical predicate “is true” does not 

function semantically or logically as predicate. All uses of “is true” are pro-sentential uses. When 

someone asserts “it is true that it is raining,” the person is asking the hearer to consider the 

sentence “it is raining” and is saying that “that, is true” where the remark “that, is true” is taken 

holistically as a prosentence, in analogy to a pronoun. A pronoun such as “she” is a substitute for 

the name of the person being referred to. Similarly, “that is true” is a substitute for the 

proposition being considered. Likewise, for the expression “it is true.” According to the pro-

sentential theory, all uses of “true” can be reduced to uses either of “that is true” or “it is true” or 

variants of these with other tenses.36 

3.10 From Truth to Knowledge 

For generations, discussions of truth have been bedeviled by the question, “how could a 

proposition be true unless we know it to be true?” Aristotle’s famous worry was that contingent 

propositions about the future, such as “there will be a sea battle tomorrow,” couldn’t be true 

now, for fear that this would deny free will to the sailors involved. Advocates of the 

Correspondence Theory and the Semantic Theory have argued that a proposition need not be 

                                                             
34 Bradley, Raymond and Norman Swartz. Possible World: an Introduction to Logic and Its Philosophy. London: 
Hacket Publishing Company, 1979. 
35 Ibid. 
36 Davidson, Donald. Inquiries into Truth and Interpretation. Oxford: Oxford University Press, 1984. 



27 
 

known in order to be true. Truth, they say, arises out of a relationship between a proposition and 

the way the world is. No one need know that that relationship holds, nor – for that matter – need 

there even be any conscious or language-using creature for that relationship to obtain. In short, 

truth is an objective feature of a proposition, not a subjective one. For a true proposition to be 

known, it must (at least) be a justified belief. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



28 
 

CHAPTER FOUR 

IS JUSTIFIED TRUE BELIEF KNOWLEDGE 

  

4.1 The Gettier Problem 

Edmund Gettier’s famous 1963 paper, “Is Justified True Belief Knowledge?”, popularized the 

claim that the definition of knowledge as justified true belief had been widely accepted 

throughout the history of philosophy.37 The extent to which this is true is highly contentious, 

since Plato himself disavowed the “justified true belief” view at the end of 

the Theaetetus.38 Regardless of the accuracy of the claim, Gettier’s paper produced major 

widespread discussion which completely reoriented epistemology in the second half of the 20th 

century, with a newfound focus on trying to provide an airtight definition of knowledge by 

adjusting or replacing the “justified true belief” view.  

If someone (S) knows some fact (p), several conditions must obtain. A proposition that S does 

not even believe cannot be a fact that S knows. Therefore, knowledge requires belief. False 

propositions cannot be facts, and so cannot be known. Therefore, knowledge requires truth. 

Finally, S’s being correct in believing that p, might merely be a luck or matter of fact. For 

instance, if you believe that your mother who is in a different location from you, is sick, and you 

have no reason for believing this except on the ground that the thought keep flashing in your 

mind. If it turns out that you are right, and your mother is truly ill, your being right about this is 

merely accidental. It is a matter of chance or luck (bad luck, in this case).39 Therefore, 

knowledge requires a third component, one that excludes the aforementioned chance. This third 

condition is called justification. 

Now, if we take these three conditions of knowledge to be not merely necessary but also 

sufficient, the, then: S knows that p if and only if p is true and S justifiably believes that p. 

According to this account, the three conditions, namely truth, belief, and justification, are 

individually necessary and collectively sufficient for knowledge of facts.40 

Recall that the justification condition is introduced to ensure that S’s belief is not true merely 

because of luck. But what must justification be, if it can ensure that? It may be thought that S’s 

belief that p is true not merely because of luck when it is reasonable or rational, from S’s own 

point of view, to take p to be true. Or, it may be thought that S’s belief is true not merely because 

of luck if that belief has a high objective probability of truth, i.e. if it is formed or sustained by 

                                                             
37 D.M. Armstrong, Belief, Truth, and Knowledge (Cambridge: Cambridge University Press), 152. 
38 Alvin Goldman, “Reliabilism: What Is Justified Belief?”. In Pappas, G.S. (ed.). Justification and Knowledge 
(Dordrecht, Holland: Reidel, 1979), 11.  
39 For an argument that true belief alone suffices for knowledge, see C. Sartwell, “Why Knowledge Is Merely True 
Belief”, The Journal of Philosophy, 89(4), (1992), 167–168.  
40 M. Steup, An Introduction to Contemporary Epistemology (Upper Saddle River, NJ: Prentice Hall, 1996), 112.  

https://en.wikipedia.org/wiki/Edmund_Gettier


29 
 

reliable cognitive processes of faculties. But on the contrary, if justification is understood in 

either of three ways, it cannot ensure against luck. 

This was precisely what Edmund Gettier demonstrated in showing that there are cases of JTB 

that are not cases of knowledge. It follows, therefore, that JTB is not sufficient for knowledge. 

Cases like that, known as Gettier’s cases arise because neither the possession of adequate 

evidence, nor origination in reliable faculties, nor the conjunction of these conditions, is 

sufficient for ensuring that a belief is not true merely because of luck. Goldman presents a well 

known case: 

Henry drives through a rural area in which what appear to be barns are mere barn façades 

(imagery), with the exception of just one. From the road he is driving on, these barns look 

exactly like real barns. But Henry happens to be looking at only one barn, and that is the only 

real barn there. Looking at this barn, he believes that there is a barn over there. Now, Henry’s 

belief is true, and his visual experience makes it reasonable for him to hold that belief. 

Furthermore, his belief originates in a reliable cognitive process, namely normal vision of 

ordinary, recognizable objects in good lighting. Notwithstanding all these, Henry’s belief is true 

in this case merely because of luck. If he had noticed one of the barn-facades instead, his belief 

may have been false. There is, therefore, broad agreement among epistemologists that Henry’s 

belief does not qualify for knowledge.41 

If JTB is, thus, not sufficient for knowledge, what further condition must be added to it? This is 

known as the Gettier problem. Some philosophers attempt to solve the Gettier problem by adding 

a fourth condition to the three conditions mentioned above, while others attempt to solve it by 

either replacing or refining the three justification conditions, and refining it depends, of course, 

on how we understand the justification condition itself. Some philosophers reject the Gettier 

problem altogether. They reject the aspiration to understand knowledge by trying to add 

something else to JTB. Some of these philosophers try to explain knowledge in terms of virtue. 

They say that to know a fact is for the truth of one’s belief to manifest epistemic virtue.42 Some 

of them also try to explain knowledge by identifying it as a genus of many familiar species. They 

say that knowledge is the most general factive mental state operator.43 Still other such 

philosophers try to explain knowledge by explaining its distinctive role in some other activity. 

Accordingly, to know a fact is for that fact to be a reason for which one can do or think 

something.44 In the view of others, to know a fact is to be entitled to assert that fact.45 Still, 

                                                             
41 A.I. Goldman, “Discrimination and Perceptual Knowledge”, The Journal of Philosophy, 73(20), (1976), 773–791. 
42 L.T. Zagzebski, Virtues of the Mind: An Inquiry into the Nature of Virtue and the Ethical Foundations of Knowledge 
(Cambridge: Cambridge University Press, 1996), 11;L.T. Zagzebski, “Reflective Knowledge in the Best Circles”, The 
Journal of Philosophy, 94(8), (1997), 411. 
43 T. Williamson, Knowledge and Its Limits (Oxford: Oxford University Press, 2002), 11.  
44 J. Hyman, “How Knowledge Works”, The Philosophical Quarterly, 49(197), (1999), 433. 
45 T. Williamson, Knowledge and Its Limits, 12. 



30 
 

according to others, to know a fact is to a trustworthy informant concerning whether than fact 

obtains. 

Finally, there are those who think that the question “what is it to know a fact?” is misconceived. 

For them, the verb “to know” does not do the work of denoting anything, but does a different 

kind of work altogether, for instance, the work of assuring one’s listeners concerning some fact 

or other, or the work of indicating to one’s audience that a particular person is a trustworthy 

informant concerning some matter.46 

To summarize, Edmund Gettier called into question the common conception of knowledge as 

justified true belief. In just two and a half pages, Gettier argued that there are situations in which 

one’s belief may be justified and true, yet fail to count as knowledge. That is, Gettier contended 

that while justified belief in a true proposition is necessary for that proposition to be known, it is 

not sufficient. 

According to Gettier, there are certain circumstances in which one does not have knowledge, 

even when all of the above conditions are met. Gettier proposed two thought experiments, which 

have become known as Gettier cases, as counterexamples to the classical account of 

knowledge.47 One of the cases involves two men, Smith and Jones, who are awaiting the results 

of their applications for the same job. Each man has ten coins in his pocket. Smith has excellent 

reasons to believe that Jones will get the job (the head of the company told him); and 

furthermore, Smith knows that Jones has ten coins in his pocket (he recently counted them). 

From this Smith infers: “The man who will get the job has ten coins in his pocket.” However, 

Smith is unaware that he also has ten coins in his own pocket. Furthermore, it turns out that 

Smith, not Jones, is going to get the job. While Smith has strong evidence to believe that Jones 

will get the job, he is wrong. Smith therefore has a justified true belief that the man who will get 

the job has ten coins in his pocket; however, according to Gettier, Smith does not know that the 

man who will get the job has ten coins in his pocket, because Smith’s belief is “...true by virtue 

of the number of coins in Jones’s pocket, while Smith does not know how many coins are in 

Smith’s pocket, and bases his belief... on a count of the coins in Jones’s pocket, whom he falsely 

believes to be the man who will get the job.”48   These cases fail to be knowledge because the 

subject’s belief is justified, but only happens to be true by virtue of luck. In other words, he made 

the correct choice (believing that the man who will get the job has ten coins in his pocket) for the 

wrong reasons. Gettier then goes on to offer a second similar case, providing the means by which 

the specifics of his examples can be generalized into a broader problem for defining knowledge 

in terms of justified true belief. 

 

 

                                                             
46 E. Craig, Knowledge and the State of Nature,66. 
47 Alvin Goldman, “Reliabilism: What Is Justified Belief?”, 11. 
48“Certainty,” Stanford Encyclopedia of Philosophy. Retrieved 28 October, 2021. 

https://en.wikipedia.org/wiki/Thought_experiment
https://en.wikipedia.org/wiki/Counterexample
https://plato.stanford.edu/archives/sum2018/entries/certainty/


31 
 

4.2 Responses to Gettier’s Problem 

There have been various notable responses to the Gettier problem. Typically, they have involved 

substantial attempts to provide a new definition of knowledge that is not susceptible to Gettier-

style objections, either by providing an additional fourth condition that justified true beliefs must 

meet to constitute knowledge, or proposing a completely new set of necessary and sufficient 

conditions for knowledge. While there have been far too many published responses for all of 

them to be mentioned, some of the most notable responses are discussed below. 

 

4.2.1 No False Premises Response 

One of the earliest suggested replies to Gettier, and perhaps the most intuitive ways to respond to 

the Gettier problem, is the “no false premises” response, sometimes also called the “no false 

lemmas” response. Most notably, this reply was defended by David Malet Armstrong in his 1973 

book, Belief, Truth, and Knowledge.49 The basic form of the response is to assert that the person 

who holds the justified true belief (for instance, Smith in Gettier’s first case) made the mistake of 

inferring a true belief (e.g. The person who will get the job has ten coins in his pocket) from a 

false belief (e.g. Jones will get the job). Proponents of this response therefore propose that we 

add a fourth necessary and sufficient condition for knowledge, namely, the justified true belief 

must not have been inferred from a false belief. 

This reply to the Gettier problem is simple, direct, and appears to isolate what goes wrong in 

forming the relevant beliefs in Gettier cases. However, the general consensus is that it 

fails.50 This is because while the original formulation by Gettier includes a person who infers a 

true belief from a false belief, there are many alternate formulations in which this is not the case. 

Take, for instance, a case where an observer sees what appears to be a dog walking through a 

park and forms the belief: “There is a dog in the park”. In fact, it turns out that the observer is not 

looking at a dog at all, but rather a very lifelike robotic facsimile of a dog. However, unknown to 

the observer, there is in fact a dog in the park, albeit one standing behind the robotic facsimile of 

a dog. Since the belief “There is a dog in the park” does not involve a faulty inference, but is 

instead formed as the result of misleading perceptual information, there is no inference made 

from a false premise. It therefore seems that while the observer does in fact have a true belief 

that her perceptual experience provides justification for holding, she does not actually know that 

there is a dog in the park. Instead, she just seems to have formed a lucky justified true belief.51 

4.2.2 Reliabilist Response 

Reliabilism has been a significant line of response to the Gettier problem among philosophers, 

originating with work by Alvin Goldman in the 1960s. According to reliabilism, a belief is 

                                                             
49Bimal Krishna Matilal, Perception: An essay on Classical Indian Theories of Knowledge (Oxford: India, 2002). The 
Gettier problem is dealt with in Chapter 4, Knowledge as a mental episode. The thread continues in the next 
chapter Knowing that one knows. 
50 Alvin Goldman, “Reliabilism: What Is Justified Belief?” 
51 Ibid. 

https://en.wikipedia.org/wiki/Necessity_and_sufficiency#Simultaneous_necessity_and_sufficiency
https://en.wikipedia.org/wiki/Necessity_and_sufficiency#Simultaneous_necessity_and_sufficiency
https://en.wikipedia.org/wiki/David_Malet_Armstrong
https://en.wikipedia.org/wiki/Alvin_Goldman
https://en.wikipedia.org/wiki/Bimal_Krishna_Matilal


32 
 

justified (or otherwise supported in such a way as to count towards knowledge) only if it is 

produced by processes that typically yield a sufficiently high ratio of true to false beliefs. In 

other words, this theory states that a true belief counts as knowledge only if it is produced by a 

reliable belief-forming process. Examples of reliable processes include standard perceptual 

processes, remembering, good reasoning, and introspection.52 

One commonly discussed challenge for reliabilism is the case of Henry and the barn façades.53 In 

this thought experiment, a man, Henry, is driving along and sees a number of buildings that 

resemble barns. Based on his perception of one of these, he concludes that he is looking at a 

barn. While he is indeed looking at a barn, it turns out that all of the other barn-like buildings he 

saw were façades. According to the challenge, Henry does not know that he has seen a barn, 

despite his belief being true, and despite his belief having been formed on the basis of a reliable 

process (i.e. his vision), since he only acquired his reliably formed true belief by accident.54 In 

other words, since he could have just as easily been looking at a barn façade and formed a false 

belief, the reliability of perception in general does not mean that his belief was not merely 

formed luckily, and this luck seems to preclude him from knowledge.  

4.2.3 Infallibilist Response 

One less common response to the Gettier problem is defended by Richard Kirkham, who has 

argued that the only definition of knowledge that could ever be immune to all counterexamples is 

the infallibilist definition.55 To qualify as an item of knowledge, goes the theory, a belief must 

not only be true and justified, the justification of the belief must necessitate its truth. In other 

words, the justification for the belief must be infallible. 

While infallibilism is indeed an internally coherent response to the Gettier problem, it is 

incompatible with our everyday knowledge ascriptions. For instance, as the Cartesian 

skeptic will point out, all of my perceptual experiences are compatible with a skeptical scenario 

in which I am completely deceived about the existence of the external world, in which case most 

(if not all) of my beliefs would be false.56 The typical conclusion to draw from this is that it is 

possible to doubt most (if not all) of my everyday beliefs, meaning that if I am indeed justified in 

holding those beliefs, that justification is not infallible. For the justification to be infallible, my 

reasons for holding my everyday beliefs would need to completely exclude the possibility that 

those beliefs were false. Consequently, if a belief must be infallibly justified in order to 

constitute knowledge, then it must be the case that we are mistaken in most (if not all) instances 

in which we claim to have knowledge in everyday situations.57 While it is indeed possible to bite 

the bullet and accept this conclusion, most philosophers find it implausible to suggest that we 

                                                             
52Robert Nozick, Philosophical Explanations (Harvard University Press, 1981), 172. 
53 Alvin Goldman, “Reliabilism: What Is Justified Belief?” 
54D.M. Armstrong, Belief, Truth and Knowledge (Cambridge University Press, 1973). 
55 Simon Blackburn, Think: A Compelling Introduction to Philosophy (Oxford University Press), 43. 
56 Cf. Jennifer Nagel, “Knowledge as a Mental State”, Oxford Studies in Epistemology Volume 4, (Oxford: Oxford 
University Press, 2013), 274, 
57 Anthony Brueckner, “Williamson on the primeness of knowing”. Analysis. 62(275), (2002),197. 

https://en.wikipedia.org/wiki/Richard_Kirkham
https://en.wikipedia.org/wiki/Infallibilism
https://en.wikipedia.org/wiki/Cartesian_skepticism
https://en.wikipedia.org/wiki/Cartesian_skepticism
https://archive.org/details/isbn_9780674664791
https://archive.org/details/belieftruthknowl0000arms
https://archive.org/details/thinkcompellingi00bla_kzi


33 
 

know nothing or almost nothing, and therefore reject the infallibilist response as collapsing 

into radical skepticism.58 

4.2.4 Indefeasibility Condition 

Another possible candidate for the fourth condition of knowledge is indefeasibility. Defeasibility 

theory maintains that there should be no overriding or defeating truths for the reasons that justify 

one’s belief. For example, suppose that person S believes he saw Tom steal a book from the 

library and uses this to justify the claim that Tom stole a book from the library. A possible 

defeater or overriding proposition for such a claim could be a true proposition like, “Tom’s 

identical twin Sam is currently in the same town as Tom.” When no defeaters of one’s 

justification exist, a subject would be epistemologically justified. 

In a similar vein, the Indian philosopher B.K. Matilal drew on the Navya-

Nyāya fallibilist tradition to respond to the Gettier problem. Nyaya theory distinguishes 

between know p and know that one knows p—these are different events, with different causal 

conditions. The second level is a sort of implicit inference that usually follows immediately the 

episode of knowing p (knowledge simpliciter). The Gettier case is examined by referring to a 

view of Gangesha Upadhyaya (late 12th century), who takes any true belief to be knowledge; 

thus a true belief acquired through a wrong route may just be regarded as knowledge simpliciter 

on this view. The question of justification arises only at the second level, when one considers the 

knowledge-hood of the acquired belief. Initially, there is lack of uncertainty, so it becomes a true 

belief. But at the very next moment, when the hearer is about to embark upon the venture 

of knowing whether he knows p, doubts may arise. “If, in some Gettier-like cases, I am wrong in 

my inference about the knowledge-hood of the given occurrent belief (for the evidence may be 

pseudo-evidence), then I am mistaken about the truth of my belief—and this is in accordance 

with Nyaya fallibilism: not all knowledge-claims can be sustained.”59 

4.2.5 Tracking Condition 

Robert Nozick has offered a definition of knowledge according to which S knows that P if and 

only if: 

 P is true; 

 S believes that P; 

 if P were false, S would not believe that P; 

 if P were true, S would believe that P.60 

Nozick argues that the third of these conditions serves to address cases of the sort described by 

Gettier. He further claims this condition addresses a case of the sort described by D.M. 

                                                             
58 Cf. Jennifer Nagel, “Knowledge as a Mental State”, 293. 
59 Hilary Kornblith, Knowledge and its Place in Nature (Oxford: Oxford University Press, 2002). 
60Robert Nozick, Philosophical Explanations, 177. 

https://en.wikipedia.org/wiki/Philosophical_skepticism
https://en.wikipedia.org/wiki/Bimal_Krishna_Matilal
https://en.wikipedia.org/wiki/Navya-Ny%C4%81ya
https://en.wikipedia.org/wiki/Navya-Ny%C4%81ya
https://en.wikipedia.org/wiki/Fallibilist
https://en.wikipedia.org/wiki/Gangesha_Upadhyaya
https://en.wikipedia.org/wiki/Robert_Nozick
https://en.wikipedia.org/wiki/D.M._Armstrong
https://archive.org/details/isbn_9780674664791


34 
 

Armstrong:61 A father believes his daughter is innocent of committing a particular crime, both 

because of faith in his baby girl and (now) because he has seen presented in the courtroom a 

conclusive demonstration of his daughter's innocence. His belief via the method of the courtroom 

satisfies the four subjunctive conditions, but his faith-based belief does not. If his daughter were 

guilty, he would still believe her innocence, on the basis of faith in his daughter; this would 

violate the third condition. 

The British philosopher Simon Blackburn has criticized this formulation by suggesting that we 

do not want to accept as knowledge beliefs which, while they track the truth (as Nozick’s 

account requires), are not held for appropriate reasons. He says that “we do not want to award 

the title of knowing something to someone who is only meeting the conditions through a defect, 

flaw, or failure, compared with someone else who is not meeting the conditions.”62 In addition to 

this, externalist accounts of knowledge, such as Nozick’s, are often forced to reject closure in 

cases where it is intuitively valid. 

An account similar to Nozick’s has also been offered by Fred Dretske, although his view focuses 

more on relevant alternatives that might have obtained if things had turned out differently. Views 

of both the Nozick variety and the Dretske variety have faced serious problems suggested 

by Saul Kripke.63 

4.2.6 Knowledge-First Response 

Timothy Williamson has advanced a theory of knowledge according to which knowledge is not 

justified true belief plus some extra conditions, but primary. In his book Knowledge and its 

Limits, Williamson argues that the concept of knowledge cannot be broken down into a set of 

other concepts through analysis—instead, it is sui generis. Thus, according to Williamson, 

justification, truth, and belief are necessary but not sufficient for knowledge.  Williamson is also 

known for being one of the only philosophers who take knowledge to be a mental state;64 most 

epistemologists assert that belief (as opposed to knowledge) is a mental state. As such, 

Williamson's claim has been seen to be highly counterintuitive.  

Today there is still little consensus about whether any set of conditions succeeds in providing a 

set of necessary and sufficient conditions for knowledge, and many contemporary 

epistemologists have come to the conclusion that no such exception-free definition is 

possible.65 However, even if justification fails as a condition for knowledge as some 

philosophers claim, the question of whether or not a person has good reasons for holding a 

particular belief in a particular set of circumstances remains a topic of interest to contemporary 

epistemology and is unavoidably linked to questions about rationality.   

                                                             
61 Duncan Pritchard, John Turri, Stanford Encyclopedia of Philosophy. Retrieved 28 October, 2021. 
62 Duncan Pritchard, “Recent Work on Epistemic Value,” American Philosophical Quarterly, 44 (2), (2007), 85–110. 
63 Cf. Alvin Goldman, “Reliabilism: What Is Justified Belief?” 
64 Cf. Jonathan L. Kvanvig, The Value of Knowledge and the Pursuit of Understanding (Cambridge University Press, 
2003). 
65 Ibid. 

https://en.wikipedia.org/wiki/D.M._Armstrong
https://en.wikipedia.org/wiki/Simon_Blackburn
https://en.wikipedia.org/wiki/Fred_Dretske
https://en.wikipedia.org/wiki/Saul_Kripke
https://en.wikipedia.org/wiki/Timothy_Williamson
https://en.wikipedia.org/wiki/Knowledge_and_its_Limits
https://en.wikipedia.org/wiki/Knowledge_and_its_Limits
https://en.wikipedia.org/wiki/Sui_generis
https://en.wikipedia.org/wiki/Necessary_and_sufficient
https://books.google.com/books?id=ILTIEjvbeLoC


35 
 

CHAPTER FIVE 

THE NATURE OF JUSTIFICATION 

5.1 Internalism and Externalism 

A central debate about the nature of justification is a debate between epistemological externalists 

on the one hand and epistemological internalists on the other. While epistemic externalism first 

arose in attempts to overcome the Gettier problem, it has flourished in the time since as an 

alternative way of conceiving of epistemic justification. The initial development of epistemic 

externalism is often attributed to Alvin Goldman, although numerous other philosophers have 

worked on the topic in the time since.66 

Externalists hold that factors deemed external meaning outside of the psychological states of 

those who gain knowledge, can be conditions of justification. For example, an externalist 

response to the Gettier problem is to say that for a justified true belief to count as knowledge, 

there must be a link or dependency between the belief and the state of the external world. 

Usually, this is understood to be a causal link. Such causation, to the extent that it is outside the 

mind, would count as an external, knowledge-yielding condition. Internalists, on the other hand, 

assert that all knowledge-yielding conditions are within the psychological states of those who 

gain knowledge. 

Though unfamiliar with the internalist/externalist debate himself, many point to René 

Descartes as an early example of the internalist path to justification. He wrote that because the 

only method by which we perceive the external world is through our senses, and that, because 

the senses are not infallible, we should not consider our concept of knowledge infallible. The 

only way to find anything that could be described as "indubitably true", he advocates, would be 

to see things “clearly and distinctly.”67 He argued that if there is an omnipotent, good being who 

made the world, then it's reasonable to believe that people are made with the ability to know. 

However, this does not mean that man’s ability to know is perfect. God gave man the ability to 

know but not with omniscience. Descartes said that man must use his capacities for knowledge 

correctly and carefully through methodological doubt.68 

The dictum “Cogito ergo sum” (I think, therefore I am) is also commonly associated with 

Descartes' theory. In his own methodological doubt—doubting everything he previously knew so 

he could start from a blank slate—the first thing that he could not logically bring himself to 

doubt was his own existence: “I do not exist” would be a contradiction in terms. The act of 

saying that one does not exist assumes that someone must be making the statement in the first 

place. Descartes could doubt his senses, his body, and the world around him—but he could not 

deny his own existence, because he was able to doubt and must exist to manifest that doubt. 

Even if some “evil genius” were deceiving him, he would have to exist to be deceived. This one 

                                                             
66 Ibid. 
67 Alan H. Goldman, “Appearing as Irreducible in Perception.” Philosophy and Phenomenological Research, 37(2), 
147. 
68Richard L. Kirkham, Mind, 93 (372), (1984), 503. 

https://en.wikipedia.org/wiki/Alvin_Goldman
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Alan_H._Goldman


36 
 

sure point provided him with what he called his Archimedean point, in order to further develop 

his foundation for knowledge. Simply put, Descartes’ epistemological justification depended on 

his indubitable belief in his own existence and his clear and distinct knowledge of God.69 

5.2 Causal theory and naturalized epistemology 

In an earlier paper that predates his development of reliabilism, Alvin Goldman writes in his 

“Causal Theory of Knowing” that knowledge requires a causal link between the truth of a 

proposition and the belief in that proposition.70 A similar view has also been defended by Hilary 

Kornblith in Knowledge and its Place in Nature, although his view is meant to capture an 

empirical scientific conception of knowledge, not an analysis of the everyday concept 

“knowledge.”71 Kornblith, in turn, takes himself to be elaborating on the naturalized 

epistemology framework first suggested by W.V.O. Quine. 

5.3 The Value Problem (Knowledge v Belief) 

We generally assume that knowledge is more valuable than mere true belief. If so, what is the 

explanation? A formulation of the value problem in epistemology first occurs in Plato’s Meno. 

Socrates points out to Meno that a man who knew the way to Larissa could lead others there 

correctly. But so, too, could a man who had true beliefs about how to get there, even if he had 

not gone there or had any knowledge of Larissa. Socrates says that it seems that both knowledge 

and true opinion can guide action. Meno then wonders why knowledge is valued more than true 

belief and why knowledge and true belief are different. Socrates responds that knowledge is 

more valuable than mere true belief because it is tethered or justified. Justification, or working 

out the reason for a true belief, locks down true belief.72 

The problem is to identify what (if anything) makes knowledge more valuable than mere true 

belief, or that makes knowledge more valuable than a mere minimal conjunction of its 

components, such as justification, safety, sensitivity, statistical likelihood, and anti-Gettier 

conditions, on a particular analysis of knowledge that conceives of knowledge as divided into 

components (to which knowledge-first epistemological theories, which posit knowledge as 

fundamental, are notable exceptions).73 The value problem re-emerged in the philosophical 

literature on epistemology in the twenty-first century following the rise of virtue epistemology in 

the 1980s, partly because of the obvious link to the concept of value in ethics.74 

5.4 Virtue Epistemology: A Solution to the Value Problem 

                                                             
69“Epistemic Contextualism,” Stanford Encyclopedia of Philosophy. Retrieved 20 October 2021. 
70 Alvin I. Goldman & E.J. Olsson, E.J. “Reliabilism and the Value of Knowledge.” In Haddock, A., Millar, A. & 
Pritchard, D. (eds.). Epistemic Value (Oxford University Press, 2009), 24. 
71 Ibid. 
72 Jonathan Kvanvig, The Value of Knowledge and the Pursuit of Understanding (Cambridge; New York: Cambridge 
University Press, 2003), 5. 
73 Ibid. 
74 See Laurence Bonjour, The Structure of Empirical Knowledge, (Cambridge, MA: Harvard University Press, 1985). 

https://en.wikipedia.org/wiki/Alvin_Goldman
https://en.wikipedia.org/wiki/Causal_Theory_of_Knowledge
https://en.wikipedia.org/wiki/Causal_chain
https://en.wikipedia.org/wiki/Hilary_Kornblith
https://en.wikipedia.org/wiki/Hilary_Kornblith
https://en.wikipedia.org/wiki/Naturalized_epistemology
https://en.wikipedia.org/wiki/Naturalized_epistemology
https://en.wikipedia.org/wiki/W.V.O._Quine
https://en.wikipedia.org/wiki/Plato
https://en.wikipedia.org/wiki/Virtue_epistemology
https://plato.stanford.edu/archives/sum2018/entries/contextualism-epistemology/


37 
 

In contemporary philosophy, epistemologists have defended virtue epistemology as a solution to 

the value problem. They argue that epistemology should also evaluate the “properties” of people 

as epistemic agents (i.e. intellectual virtues), rather than merely the properties of propositions 

and propositional mental attitudes. 

The value problem has been presented as an argument against epistemic reliabilism. Zagzebski, 

for instance, analogizes the value of knowledge to the value of espresso produced by an espresso 

maker: “The liquid in this cup is not improved by the fact that it comes from a reliable espresso 

maker. If the espresso tastes good, it makes no difference if it comes from an unreliable 

machine.”75 For Zagzebski, the value of knowledge deflates to the value of mere true belief. She 

assumes that reliability in itself has no value or disvalue, but Goldman and Olsson disagree. 

They point out that Zagzebski’s conclusion rests on the assumption of veritism: all that matters is 

the acquisition of true belief.76 To the contrary, they argue that a reliable process for acquiring a 

true belief adds value to the mere true belief by making it more likely that future beliefs of a 

similar kind will be true. By analogy, having a reliable espresso maker that produced a good cup 

of espresso would be more valuable than having an unreliable one that luckily produced a good 

cup because the reliable one would more likely produce good future cups compared to the 

unreliable one. 

The value problem is important to assessing the adequacy of theories of knowledge that conceive 

of knowledge as consisting of true belief and other components. According to Kvanvig, an 

adequate account of knowledge should resist counterexamples and allow an explanation of the 

value of knowledge over mere true belief. Should a theory of knowledge fail to do so, it would 

prove inadequate.77 

One of the more influential responses to the problem is that knowledge is not particularly 

valuable and is not what ought to be the main focus of epistemology. Instead, epistemologists 

ought to focus on other mental states, such as understanding.78 Advocates of virtue epistemology 

have argued that the value of knowledge comes from an internal relationship between the knower 

and the mental state of believing.79 

5.5 Cognitive Success vis a vis Epistemic Harms 

The question, therefore, arises, what makes it the case that something counts as a form of 

cognitive success? For instance, why think that knowing the school vice chancellor is a cognitive 

success, rather than any other cognitive state? Not ever cognitive state enjoys cognitive success. 

Knowing, understanding, mastering, etc, are all cognitive successes. But confidence in a 

                                                             
75“The Analytic/Synthetic Distinction,” Stanford Encyclopedia of Philosophy, Retrieved October 29, 2021. 
76 Cf. G. Russell, Truth in Virtue of Meaning: A Defence of the Analytic/Synthetic Distinction (Oxford: Oxford 
University Press, 2008). 
77 Jonathan L. Kvanvig, The Value of Knowledge and the Pursuit of Understanding. 
78 Edward N. Zalta (ed.). “Foundational Theories of Epistemic Justification,” Stanford Encyclopedia of Philosophy. 
Accessed October, 29, 2021. 
79 Jonathan L. Kvanvig, The Value of Knowledge and the Pursuit of Understanding. 

https://en.wikipedia.org/wiki/Reliabilism
https://en.wikipedia.org/wiki/Jonathan_Kvanvig
https://plato.stanford.edu/entries/analytic-synthetic
https://books.google.com/books?id=ILTIEjvbeLoC
https://en.wikipedia.org/wiki/Edward_N._Zalta
https://plato.stanford.edu/entries/justep-foundational/
https://en.wikipedia.org/wiki/Stanford_Encyclopedia_of_Philosophy
https://books.google.com/books?id=ILTIEjvbeLoC


38 
 

proposition, for instance, is not a cognitive success in and of itself. Inasmuch as an agent can 

hold confidence in the right circumstances and for the right reasons (in which case, it is partly 

constitutive of an agent’s cognitive success), it is also possible that then agent can hold 

confidence in the wrong circumstance and for the wrong reasons. One can even be confident that 

what is not, is. What makes the difference? 

The idea of cognitive success can be explained in three ways, namely contractualism, 

consequentialism, or constitutivism. The contractualists say that a particular cognitive state 

counts as a kind of success because counting it as such severs certain widely held practical 

interest. For instance, we describe a person as ‘knowing’ something as a way of showing that his 

testimony with respect to that thing is to be trusted.80 The consequentialist says that a particular 

cognitive state counts as a success because it tends to constitute or to promote some important 

benefit. According to some consequentialists, the benefit in question is that of having true beliefs 

and lacking false beliefs.81 According to others, it is the benefit of having a comprehensive 

understanding of reality. For others still, it is a benefit that I not narrowly epistemic, like living a 

good life. Lastly, the constitutivists would say that a particular cognitive state counts as a success 

if it is the constitutive aim of some feature of our lives to achieve that aim.82 For instance, the 

constitutivist might say that knowledge is a kind of cognitive success by virtue of being the 

constitutive aim of all human activity. 

The above three answers will depict three different kinds of cognitive success. Each of the 

answer is correct for a particular kind of success. Consider, for example, the difference between 

the kind of success involved in having a state that is fitting (like holding a belief knowledgeable), 

and the kind of success involved in having a state that is valuable (like holding a belief the 

holding of which is beneficial). An example of the former would be: the capital of Nigeria is 

Abuja, while that of the later would be: God exists. Perhaps the constitutivist can explain the 

former kind of success better than the consequentialist can, but the consequentialist can explain 

the latter kind of success better than the constitutivist can. Of course, if and when the demands of 

these different kinds of success conflict, the agent will face the question of how to proceed. 

Much recent work in epistemology has attempted to dress the question.83 

Now, these different ways of understanding cognitive success each gives rise to a different 

understanding of the diverse ways in which cognitive success can be obstructed, and so a 

different understanding of the ways in which an agent may be harmed by such obstructions. 

Obstructing an agent’s cognitive success constitutes an epistemic harm. In a situation in which 

                                                             
80 E. Craig, Knowledge and the State of Nature : An Essay in Conceptual Synthesis (Oxford: Clarendon Press, 1990), 
64-65. 
81 L. BonJour, The Structure of Empirical Knowledge (Cambridge, MA: Harvard University Press, 1985).  R. Audi, The 
Structure of Justification, (Cambridge: Cambridge University Press, 1993). 
82 C. Korsgaard, Self-Constitution: Agency, Identity, and Integrity (Oxford: Oxford University Press, 2009), 7. 
83 M. McCormick, Believing Against the Evidence: Agency and the Ethics of Belief, New York: Routledge, 2015), and 
S. Rinard, “No Exception for Belief,” Philosophy and Phenomenological Research, 94(1) (2017a), 121. 



39 
 

false testimony would be an epistemic harm, dishonest testimony would be an epistemic wrong. 

Insinuation, inattention, and false indoctrination can all constitute epistemic harms as each of 

them can obstruct, and sometimes wrongly obstruct an agent’s cognitive success. 

For example, one can mislead you into drawing false conclusions, even if what one says is true. 

For instance, when I say, “the victims were killed by a herdsman,” even if what I say is literally 

true, it can mislead the hearer into thinking that the killer’s being a herdsman is a relevant 

explanation to his crime. Similarly, one can harm you by getting you to think poorly of your own 

capacity to understand a subject by refusing to pay attention to what you think or say. Also, one 

can harm you by indoctrinating you in a view so strong that you lose the ability to consider 

alternative views. 

The epistemic harms we just mentioned occur frequently in the course of daily life, and they are 

typically constituted by some particular acts that we perform, such as lending greater credence to 

the word of a man over that of a woman, or using rhetorical devices to insinuate things that one 

does not know to be true. Recent work in feminist epistemology has helped us to gain an 

appreciation of how widespread this phenomenon is.84 

Sometimes the harm might even be built into our practice of epistemic appraisal perhaps even a 

tendency that is somehow constitutive of that very practice. Suppose, for instance, that it is 

constitutive of our practice of epistemic appraisal to count someone as knowing a fact or being 

knowledgeable only if he possesses a doctorate degree from a recognized academic institution. 

Whatever may be said in favour of our practice’s having such a feature, one of its effects is clear: 

those individuals who are most excellently knowledgeable with regard to certain facts will find 

that the deliverance of their unique cognitive sensitivities is not counted as knowledge. And so, 

these same individuals will not be granted the same authority or credibility as the doctorate 

degree holders, even when these latter are less knowledgeable and less cognitively sensitive to 

the range of facts in question. 

5.6 Opinion and Knowledge 

In all senses of knowledge and opinion, a belief justifiably known to be true in knowledge while 

a belief not known to be true is opinion. In this case, all knowledge is true but not all opinions 

are true. Every proposition known to be true (knowledge) is believed to be true; but not every 

proposition believed to be true (opinion) is known to be true. Each of a person’s beliefs, whether 

knowledge or opinion, is the end result of a particular thought process, with a conclusive act – 

judgment that something is the case.  

Platonic epistemology holds that knowledge of ideas is innate, so that learning is the 

development of ideas buried deep in the soul, often under the midwife-like guidance of an 

interrogator. In several dialogues by Plato, the character Socrates presents the view that each soul 

                                                             
84 see M. Fricker, Epistemic Injustice: Power and the Ethics of Knowing (Oxford: Oxford University Press, 2007); K. 
Dotson, “Conceptualizing Epistemic Oppression”, Social Epistemology, 28(2), (2014), 115. 



40 
 

existed before birth with the Form of the Good and a perfect knowledge of ideas. Thus, when an 

idea is “learned” it is actually just “recalled.”85 

Plato wished to know the difference between knowledge and opinion. His idea is that something 

needs to be added to opinion to get knowledge. That something else is “truth,” “justification,” 

“reliability,” etc. Plato, thus, drew a sharp distinction between knowledge, which is certain, and 

mere true opinion, which is not certain. According to him, opinions derive from the shifting 

world of sensation; knowledge derives from the world of timeless Forms or essences. In the 

republic, these concepts were illustrated using the metaphor of the sun, the analogy of the 

divided line, and the allegory of the cave. 

5.6.1 Metaphor of the Sun 

In the Republic (507b-509c) Plato’s Socrates uses the sun as a metaphor for the source of 

“intellectual illumination,” which he held to be The Form of the Good. It starts with the eye, 

which Socrates says is unusual among the sense organs in that it needs a medium, namely light, 

in order to operate. The strongest and best source of light is the sun; with it, we can discern 

objects clearly. Analogously for intelligible objects, The Form of the Good, is necessary in order 

to understand any particular thing. Thus, if we attempt to understand why things are as they are, 

and what general categories can be used to understand various particulars around us, without 

reference to any forms (universals) we will fail completely. By contrast, the domain where truth 

and reality shine resplendent is none other than Plato’s world of forms – illustrated by the highest 

of the forms, that of the good. It is only here that knowledge (and not opinion) consists. 

5.6.2 The Divided Line 

In Plato’s republic, Book VI, the divided line has two parts that represent the intelligible world 

and the smaller visible world. Each of those two parts is divided, the segments within the 

intelligible world represent higher and lower forms and the segments within the visible world 

represent ordinary visible objects and their shadows, reflections, and other representations. The 

line segments are unequal and their lengths represent their comparative clearness and obscurity 

and their comparative reality and truth, as well as whether we have knowledge or instead mere 

opinion of the object 

 

 

 

 

 

                                                             
85  



41 
 

CHAPTER SIX 

THEORIES OF JUSTIFICATION 

6.1 Introductory Discourse 

What precisely is involved in knowing a fact? Whatever it is, it is widely recognized that some of 

our cognitive successes fall short of knowledge. An agent may, for example, conduct himself in a 

way that is intellectually infallible, and yet still end up believing a false proposition. You have 

every reason to believe that your birthday is December 1: it says so on your birth certificate and 

all of your medical records, and everyone in your family insists that it is December 1. 

Nevertheless, if all of this evidence is the result of a time-keeping mistake made at the time of 

our birth, your belief about your birthday is false, despite being well justified. Debates 

concerning the nature of justification can be understood as debates concerning the nature of such 

non-knowledge-guaranteeing cognitive successes as the one given above. 

6.2 Deontological and Non-Deontological Justification 

How is the term ‘justification’ used in ordinary language? Here is an example: I asked you a 

question (say, how much does our father have in his account), and you told me a lie (say, I don’t 

know – whereas you know). Were you justified in lying? Demola thinks you were, because my 

question was an inappropriate one, the answer to which was none of my business. What might 

Demola mean when he thinks that you were justified in responding with a lie? She means that 

you were under no obligation to refrain from lying. Due to the inappropriateness of my question, 

it was not your duty to tell the truth. This understanding of justification is commonly labeled 

deontological justification. 

6.3 Deontological Justification 

S is justified in doing x if and only if S is not obliged to refrain from doing x. More 

appropriately: 

S is justified in believing that p if and only S is not obliged to refrain 

from believing that p. 

The key term here is obligation or duty. What kind of obligations are relevant when we wish to 

ask whether or not a belief (rather than an action) is justified or unjustified? The answer is this: 

when we evaluate an action, we are interested in assessing the action from either a moral or a 

prudential point of view, whereas when it comes to beliefs, we are interested in the pursuit of 

truth, or of understanding, or of knowledge. 

Philosophers differ in their response about what we must do in the pursuit of such distinctively 

epistemic aim. According to one answer, the one favoured by evidentialists, we ought to believe 



42 
 

in accordance with our evidence86 For this answer to be helpful, we need an account of what 

“evidence” consists in, and what it mean to believe in accordance with it. The deontological 

understanding of the concept of justification is common to the way philosophers such as 

Descartes, Locke, Moore and Chisholm have thought about justification. 

Recently, however, two main objections have been raised against conceiving of justification 

deontologically. First, it has been argued that deontological justification presupposes that we can 

have a sufficiently high degree of control over our beliefs. This objection claims that beliefs are 

akin not to actions but to things. The idea is that beliefs simply arise in or happen to us. 

Therefore, it is not suitable for deontological evaluation.87 To this objection, some advocates of 

deontological justification have replied that lack of control over our beliefs is no obstacle to 

thinking of justification as a deontological status.88 Other advocates of deontological justification 

argue that we enjoy no less control over our beliefs than we do over our intentional actions.89 

The other objection to deontological justification purports that deontological justification cannot 

suffice for an agent to have a justified belief. This claim is typically supported by describing 

cases involving either a benighted, culturally isolated society or subjects who are cognitively 

deficient. Such cases involve subjects whose cognitive limitations make it the case that they are 

under no obligation to refrain from believing as they do, but whose limitations nevertheless 

render them incapable of forming justifiable beliefs.90 

It is evident from the ongoing that those who reject deontological justification think of 

justification not deontologically, but rather as a property that a belief has when it is, in some 

sense, sufficiently likely to be true. Alston writes: “I agree that ‘justification’ is the wrong word 

for a non-deontological concept, but we seem to be stuck with it in contemporary theory of 

knowledge.”91 Hence, we may call this sufficient likelihood of justification. Let us define it as 

follows: 

6.4 Sufficient Likelihood of Justification 

S is justified in believing that p if and only if S believes that p in a way that makes 

it sufficiently likely that her belief is true. 

If we wish to pin down exactly what the likelihood at issue amounts to, we will have to deal with 

a variety of issues. Indeed, a belief can be very likely to be true in a way that is completely 

                                                             
86 T. Kelly, “The Rationality of Belief and Some Other Propositional Attitudes”, Philosophical Studies, 110(2), (2002), 
163. 
87 M. Chrisman, “Ought to Believe”:, Journal of Philosophy, 105(7), (2008), 348. 
88 R. Feldman, “Epistemic Obligations”, Philosophical Perspectives, 2 (1988), 235. 
89 M. Steup, “Believing Intentionally”, Synthese, 194(8), (2017), 2673; S. Rinard, Susanna,, 2019b, “Equal Treatment 
for Belief”, Philosophical Studies, 176(7) (2019b), 1923–1950. 
90 For a response to this objection, see M. Steup, “A Defense of Internalism”, in The Theory of Knowledge: Classical 
and Contemporary Readings, Louis P. Pojman (ed.), (Belmont, CA: Wadsworth, 1999), pp. 373–384. 
91 W.P. Alston, “Varieties of Privileged Access”, American Philosophical Quarterly, 8(3), (1989), 7ff. 



43 
 

irrelevant to the beliefs being, or not being, an instance of knowledge. In that case, it would not 

be sufficiently likely to be true in a way that is relevant to any question of justification. For 

example, suppose you believe that Buhari will win the election (p). Suppose also that our belief 

originates solely in wishful thinking. Finally, suppose that Buhari’s winning the election is 

objectively probable because it is a fact that over 80% of the electorates will vote in his favour. It 

follows that your belief that p is likely to be true. As such, it is very likely that your belief is true. 

However, since your belief is the result of wishful thinking, it would not be justified nor be an 

instance of knowledge. What we need is likelihood of truth that arises not by virtue of what the 

subject beliefs, but rather by the virtue of the way in which the subject holds, or comes to hold, 

the belief. But then we must find, in a systematic and principled way, a way of specifying the 

relevant ways of holding, or coming to hold, a belief. This endeavor raises what has been called 

the “the generality problem.”92 

For now, let us just focus on the main point. Those who prefer “sufficient likelihood 

justification” to deontological justification would say that sufficient likelihood of truth and 

deontological justification can diverge: it is possible for a belief to be deontologically justified 

without being sufficiently likely to be true. This is just what cases involving benighted cultures 

or cognitively deficient subjects are designed to show. 

6.5 How is Belief Justified? 

What makes a belief that p justified, when it is? Whether a belief is justified or unjustified, there 

is something that makes it so. Let us call the things that make a belief justified or unjustified J-

factors. But which features of a belief are J-factors? 

6.5.1 Evidentialism 

According to “evidentialists,” it is the believer’s possession of evidence for p. What is it, though, 

to possess evidence for p? Some evidentialists would say it is to be in an experience that presents 

p as being true. According to this view, if the tea in your cup tastes sweet to you, then you have 

evidence that the tea is sweet. If you feel a troubling pain in your head, you have evidence that 

you have a headache. If you have a memory of having a cup of tea for breakfast, then you have 

evidence about what you had for breakfast. And when you clearly see or intuit that a proposition 

(say, if Hyginus has more than four cars, then Hyginus has more than three cars) is true, then you 

have evidence for that proposition. 

On this view, evidence consists in perception, introspection, memory and intuition, and to 

possess evidence is to have such experiences. Therefore, according to this experientialist version 

of evidentialism, what makes you justified in believing that p is your having an experience that 

                                                             
92 See R. Feldman, Epistemology (Upper Saddle River, NJ: Prentice Hall, 2003), 19. 



44 
 

represents p as being true.93 Other versions of evidentialism might identify other factors as your 

evidence, but would still insist that those factors are the J-factors. 

6.5.2 Reliabilism 

Evidentialism is often contrasted with reliabilism, which is the view that a belief is justified if it 

results from a reliable source, where a source is reliable if it results from already established true 

beliefs. Reliabilists can also grant that the experiences mentioned in our previous discussion can 

be important to the justification of beliefs. However, they deny that justification is essentially a 

matter of having suitable experiences. Instead, they say that those experiences matter to the 

justification of beliefs not merely by virtue of being evidence in support of those beliefs, but 

more fundamentally, by virtue of being part of the reliable source of those beliefs. 

Different versions of reliabilism have been defended. Some philosophers claim that what 

justifies a belief is that it is produced by a process that is reliable.94 Others claim that what 

justifies a belief is that it is responsive to grounds that reliably co-vary with the truth of that 

belief. Still others claim that what justifies a belief is that it is formed by the virtuous exercise of 

a capacity, and so on. To understand our discussion of evidentialism and reliabilism better, we 

shall look briefly into internalism and eternalism. 

6.6 Internal vs. External 

6.7 Internalism 

Consider a science fiction scenario concerning a human brain that is removed from its skull, kept 

alive in a vat of nutrient fluid, and electrochemically stimulated to have precisely the same total 

series of experiences that you have had. Let us call such a brain BIV. A BIB would believe 

everything that you believe, and would (it is often thought) be justified in believing those things 

to precisely the same extent that you are justified in believing them. Thus, justification is 

determined solely by those internal factors that you and your fictitious brain share. This view is 

what has come to be called internalism about justification.95 

6.7.1 Approaches to Internalism 

There is no unanimity on how to understand the notion of internality among those who think that 

justification is internal, that is, what it is about the factors that you share with your BIV that 

makes those factors relevant to justification. We can distinguish between two approaches. 

According to the first, justification is internal because we enjoy a special kind of access to J-

factor: they are always recognizable on reflection. Hence, assuming certain further premises 

(which will be mentioned momentarily), justification itself is always recognizable on 

                                                             
93 R. Feldman, Epistemology, 21. 
94 A. I. Goldman, Epistemology and Cognition (Cambridge, MA: Harvard University Press, 1986), ix. 
95 L. BonJour, The Structure of Empirical Knowledge 



45 
 

reflection.96 Let us call this approach accessibility internalism. According to the second 

approach, justification is internal because J-factors are always mental states.97 Let us call this 

mentalist internalism. 

6.8 Externalism 

On the other hand, externalism is simply the denial of internalism. Externalists say that what we 

want from justification is the kind of likelihood of truth needed for knowledge, and the internal 

conditions that you share with your BIV do not generate such likelihood of truth. Hence, 

justification involves external conditions. 

Evidentialism is typically associated with internalism and reliabilsm with externalism. Let u see 

why. Evidentialism says at least two things:98 

E1: What makes one justified in believing p is nothing over and above the evidence that one 

possesses. 

E2: What evidence one possesses is fixed by one’s mental states. 

By virtue of E2, evidentialism is an instance of mentalist internalism. Whether it is also an 

instance of accessibility internalism is a more complicated issue. The conjunction of E1 and E2 

by itself implies nothing about the accessibility of justification. But mentalist internalists who 

endorse the first principle below will also be committed to accessibility internalism, and 

evidentialists who also endorse the second principle below will be committed to the accessibility 

of justification. 

6.8.1 Luminosity: One’s own mind is cognitively luminous whenever one:99 

 is in a particular mental state 

 can always recognize on reflection what mental states one is in 

 can always recognize on reflection what evidence one possesses. 

6.8.2 Necessity: The principle that determines what is evidence for what are a priori 

recognizable. Relying on a priori insight, one can therefore always recognize on reflection 

whether, or the extent, to which a particular body of evidence is evidence for p. 

Although E1 and E2 by themselves do not imply access internalism, their conjunction with 

Luminosity and Necessity may imply access internalism. 

                                                             
96 R.M. Chisholm, Theory of Knowledge, (3rd ed.), (Englewood Cliffs, NJ: Prentice-Hall, 1989), 17. 
97 R. Feldman, 2001b, “Skeptical Problems, Contextualist Solutions”, Philosophical Studies, 103(1), (2001b), 61. 
98M. Steup and E. Sosa (eds.), Contemporary Debates in Epistemology (Malden, MA: Blackwell, 2005), 78. 
99 Steup and sosa………………………… T. Williamson, Knowledge and Its Limits, (Oxford: Oxford University Press, 2002), 
ch.4. He rejects the claim that mental states are luminous. 



46 
 

Now, let us consider why reliabilsm is an externalist theory. Reliabilsm says that the justification 

of one’s belief is a function of the reliability of one’s belief sources such as memorial, perceptual 

and introspective states and processes. Even if the operations of the sources are mental states, 

their reliability is not itself a mental state. Therefore, reliabilists reject mentalist internalism. 

Moreover, insofar as the reliability of one’s belief sources is not itself recognizable by means of 

reflection, how could reflection enable us to recognize when such justification obtains? 

Reliabists who think there is no good answer to this question also reject access internalism.100 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                             
100 For works on the internalism-externalism issues, see S.C. Goldberg, “What Is the Subject-Matter of the Theory 
of Epistemic Justification?”, in Epistemic Evaluation: Purposeful Epistemology, David K. Henderson and John Greco 
(eds.), (Oxford: Oxford University Press, 2015), 204–205., among others. 



47 
 

CHAPTER SEVEN 

THE STRUCTURE OF JUSTIFICATION 

7.1 Introductory Discourse 

Epistemologists believe that there is no isolated knowledge. Knowing something requires 

knowing other things. Anyone who knows anything knows other things, for our knowledge 

forms a body – and that body has a structure. But what is this structure? Epistemologists 

generally tend to regard the structure of our knowledge as deriving from that of our justification. 

This conclusion can only become clearer as we examine some epistemological accounts of 

justification. 

7.2 Foundationalism 

According to this theory, our justified beliefs are structured like a building: they are divided into 

a foundation and a superstructure, the later resting upon the former. Beliefs belonging to the 

foundation are nonbasic and receive justification from the justified beliefs in the foundation. 

Before we evaluate this foundationalist account of justification, let us first try to spell it out more 

precisely. 

What is it for a justified belief to be basic? According to one account, what makes a justified 

belief basic is that it does not receive its justification from any other beliefs. The following 

definition captures this thought. 

7.2.1 Doxastic Basicality (DB) 

S’s justified belief that p is basic if and only if S’s belief that p is justified without owing its 

justification to any of Ss other beliefs. 

Let us consider what would qualify as an example of a basic belief according to this definition. 

Suppose you notice someone’s cap and you also notice that that cap looks blue to you. So you 

believe: 

*(B) It appears to me that that cap is blue. 

The above (B) is an example of a justified belief. Doxastic basicality tells us that (B) is basic if 

and only if it does not owe its justification to any other beliefs of yours. Therefore, if (B) is 

indeed basic, there must be some item or other to which (B) owes its justification, but that item 

will not be another belief of yours. We call this kind of basicality “doxastic” because it makes 

basicality a function of how our doxastic system (our belief system) is structured. 

7.2.2 Kinds of Foundationalism 



48 
 

Let us now turn to the question of where the justification that attaches to (B) might come from, if 

we think of basicality, as defined by doxastic basicality. Note that doxastic basicality merely tells 

us that (B) is justified. It does not tell us how precisely (B) is justified. So it does not answer that 

question. What we need in addition to it, is an account of what it is that justifies a belief such as 

(B). 

7.2.3 Privilege Foundationalism 

According to one strand of foundationalist thought (which we call privilege foundationalism), 

(B) is justified because it cannot be false, doubted, or corrected by others. On such a view, (B) is 

justified because it carries with itself an epistemic privilege such as infallibility, indubitability 

and incorrigibility (cf. Alston, 1989). Note that (B) is a belief about how the cap appears to you. 

So (B) is a belief about a perceptual experience of yours. According to this strand of 

foundationalism, the basic beliefs of a subject are introspective beliefs about his/her own mental 

states, of which perceptual experiences make up one subset. Other mental states about which a 

subject can have basic beliefs may include such things as having a headache, being tired, feeling 

happy, etc. Beliefs about external objects cannot qualify as basic, according to this kind of 

foundationalism, because it is impossible for such beliefs to enjoy the kind of epistemic 

privileges necessary for being basic. 

7.2.4 Experiential Foundationalism 

According to a different strand of foundationalism (which we call experiential foundationalism), 

(B) is justified by some further mental state of yours, but not by a further belief of yours. Indeed, 

(B) is justified by the very perceptual experience that (B) itself is about, namely the cap’s 

looking blue to you. Let (E) represent that experience. According to this alternative view, (B) 

and (E) are distinct mental states. The idea is that what justifies (B) is (E). Since (E) is an 

experience, not a belief of yours, (B) can, according to doxastic basicality, still be basic. 

7.2.5 Privilege vs. Experiential 

Privilege foundationalism is generally thought to restrict basic beliefs so that beliefs about 

contingent, mid-independent facts cannot be basic, since beliefs about such facts are generally 

thought to lack the privilege that attends our introspective beliefs about our own present mental 

states, or our beliefs a priori necessities. Experiential foundationalism is not restrictive in the 

same way. Suppose instead of (B), you belief (H): 

(H) That cap is blue. 

Unlike B, (H) is about the cap itself, and not the way the cap appears to you. Such a belief is not 

one about which we are infallible or otherwise epistemicall privileged. Privilege foundationalism 

would, therefore, classify (H) as nonbasic. However, it is quite plausible to think that E justifies 

not only (B) but (H) as well. If (E) indeed is what justifies (H), and (H) does not receive any 



49 
 

additional justification from further beliefs of yours, the (H) qualifies, according to doxastic 

basicality, as basic. 

Experiential foundationalism, thus, combines two crucial ideas: 

(i) when a justified belief is basic, its justification is not owed to any other belief; 

(ii) what in fact justifies basic beliefs are experiences. 

Under normal circumstances, perceptual beliefs such as (H) are not based on any further beliefs 

about one’s own perceptual experience. It is not clear, therefore, how privilege foundationalism 

can account for the justification of ordinary perceptual beliefs like (H).101 

Experiential foundationalism, on the other hand, has no difficulty explaining how ordinary 

perceptual beliefs are justified. According to this theory, they are justified by the perceptual 

experiences that give rise to them. This could be the reason why more preference has been given 

to experiential foundationalism by some philosophers. So far, we have articulated one conception 

of basicality, namely doxastic basicality. Below is an alternative conception. 

7.2.6 Epistemic Basicality (EB) 

S’s justified belief that p is basic if and only if S’s justification for believing that p does not 

depend on any justification S possesses for believing a further proposition, q.102 

From this, it is clear that epistemic basicality makes it more difficult for a belief to be basic that 

doxastic basicality does. To throw more light, we turn to the main question (let us call it the J-

question) that advocates of experiential foundationalism. 

7.2.7 The J-Question: EB vs. DB 

Why are perceptual experiences a source of justification? 

One way of answering the J-question is as follows: perceptual experiences are a source of 

justification only when, and only because, we have justification for taking them to be reliable.103 

Note that your having justification for believing that p does not entail that you actually believe p. 

thus, your having justification for attributing reliability to your perceptual experiences does not 

entail that you actually believe them to be reliable. 

What then might give us justification for thinking that our perceptual experiences are reliable? 

That is a complicated issue. For the purpose of this book, let us consider the following answer: 

                                                             
101 See R.A. Fumerton, Metaepistemology and Skepticism (Lanham, MD: Rowman & Littlefield, 1995), for an effort 
to clarify this 
102 Cf. M. Huemer, Skepticism and the Veil of Perception (Lanham, MD: Rowman & Littlefield Publishers, 2001), 33-
34. 
103 See S. Cohen, “Basic Knowledge and the Problem of Easy Knowledge”, Philosophy and Phenomenological 
Research, 65(2), (2002), 309–329, for an article advocating compromise positions 



50 
 

we remember that they have served us well in the past. We are supposing, then, that justification 

for attributing reliability to your perceptual experiences consists of memories of perceptual 

success. On this view, a perceptual experience (E) justifies a perceptual belief only when, and 

only because, you have suitable track-record memories that give you justification for considering 

(E) reliable. Of course this raises the question why those memories give you justification, but 

there are many different approaches to this question, as we will see more fully. 

If the above view is correct, then it is clear how doxastic basicality and epistemic basicality 

differ. Your having justification for (H) depends on your having justification for believing 

something else in addition to (H), namely that your visual experiences are reliable. As a result, 

(H) is not basic in the sense defined by epistemic basicality. However, (H) might still be basic in 

the sense defined b doxastic basicality. If you are justified in believing (H) and your justification 

is owed solely to (E) and (say, M), neither of which includes any beliefs, then your belief is 

doxastical, though not epistemically, basic 

7.2.8 Other Possible answers 

We have considered one possibility of answering the J-question, and considered how epistemic 

basicality and doxastic basicality differ, if that answer is correct. But there are other possible 

answers to the J-question. Another answer is that perceptual experiences are a source of 

justification when, and because, they are of types that reliably produce true belief. Another 

answer is that perceptual experiences are a source of justification when, and because, they are of 

types that reliably indicate the truth of their content. Yet another answer is that perceptual 

experiences are a source of justification when, and because, they have a certain phenomenology, 

namely that of presenting their content as true. It follows from this internalist answer that your 

perceptual experiences are a source of justification for you even if they are systematically 

unreliable concerning the truth of their content. 

7.3 Transfer of Justification 

Finally, let us briefly consider how justification is supposed to be transferred from basic to non-

basic beliefs. There are two options: the justificatory relation between basic and non-basic beliefs 

could be deductive or non-deductive. If we take the relation to be deductive, each of one’s non-

basic beliefs would have to be such that it can be deduced from one’s basic belief. But if we 

consider a random selection of typical beliefs we hold, it is difficult to see from which basic 

belief they could be deduced. 

Foundationalists, therefore, typically conceive of the link between the foundation and the 

superstructure in non-deductive terms. They would say that, for a given set of basic beliefs, B, to 

justify a nonbaasic belief, B*, it is not necessary that B entails B*. Instead, it is sufficient that, the 

inference from B to B* is a rational one – however such rationality is to be understood. 

 



51 
 

7.4 Coherentism 

Foundationalism says that knowledge and justification are structured like a building, consisting 

of a superstructure that rests upon a foundation. According to coherentism, this simile gets things 

wrong. Knowledge and justification are structured like a web where the strength of any given 

area depends on the strength of the surrounding areas. Coherentists, then, deny that there are any 

basic beliefs. As we have already seen, there are two different ways of conceiving of basicality. 

Consequently, there are two corresponding ways of constructing coherentism: as the denial of 

doxastic basicality or as the denial of epistemic basicality. Let us first consider coherentism as 

the denial of doxastic basicality. 

7.4.1 Doxastic Coherentism 

Every justified belief receives its justification from other beliefs in its epistemic neighborhood. 

Let us apply this thought to the cap example we considered above. Suppose again you notice 

someone’s cap and believe: 

(H) That hat is blue. 

Let us suppose that (H) is justified. According to coherentism, (H) receives its justification from 

other beliefs in the epistemic vicinity of (H). They constitute your evidence or your reason for 

taking (H) to be true. Which beliefs might make up this set of neighborhood beliefs? We will 

consider two approaches to answering this question. The first is known as inference to the best 

explanation. Such inferences generate what is called explanatory coherence.104 According to this 

approach, we must suppose that you form a belief about the way the cap appears to you in your 

perceptual experiences, and a second belief to the effect that your perceptual experience, the 

cap’s looking blue to you, is best explained by the hypothesis that (H) is true. Hence, the relevant 

set of beliefs is the following: 

(1) I am having a visual experience (E): the cap looks blue to me. 

(2) My having (E) is best explained by assuming that (H) is true. 

There are of course alternative explanations of why you have (E). Perhaps you are hallucinating 

that the cap is blue. Perhaps an evil demon makes that cap look blue to you when in fact it is red. 

Perhaps you are the sort of person to whom caps always look blue. An explanatory coherentist 

would say that, compared with these, the cap’s actual blueness is a superior explanation. That is 

why you are justified in believing (H). Note that an explanatory coherentist can also explain the 

lack of justification. Suppose that you remember that you just took a hallucinatory drug that 

makes things blue to you. That would prevent you from being justified in believing (H). The 

explanatory coherentist can account for this by pointing out that, in the case under consideration, 

the truth of (H) would not be the best explanation of why you are having experience (E). Rather, 

                                                             
104 G. Harman, Change in View: Principles of Reasoning (Cambridge, MA: MIT Press, 1986), 2. 



52 
 

your having taking the hallucinatory drug would explain your have (E) at least as the hypothesis 

(H) would explain it. That is why, according to the explanatory coherentist, you are not justified 

in believing (H). 

One challenge for explanatory coherentist is to explain what makes one explanation better than 

another. Let us use the evil demon hypothesis to illustrate this challenge. What we need is an 

explanation of why you are having (E). According to the evil demon hypothesis, you are having 

(E) because the evil demon is causing you to have it, in order to trick you. The explanatory 

coherentist would say that, if the bulk of our beliefs about the mind-independent world are 

justified, then this “evil demon” hypothesis is a bad explanation of why you are having (E). But 

why is it bad? What we need to answer in this question is a general and principled account of 

what makes one explanation better than another. Suppose we appeal to the fact that you are 

not justified in believing in the existence of evil demons. The general idea would be this: If there 

are two competing explanations, E1 and E2, and E1 consists of or includes a proposition that you 

are not justified in believing whereas E2 does not, then E2 is better than E1. The problem with 

this idea is that it puts the cart before the horse. 

Explanatory coherentism is supposed to help us understand what it is for beliefs to be justified. It 

does not do that if it accounts for the difference between better and worse explanations by 

making use of the difference between justified and unjustified belief. If explanatory coherentism 

were to proceed in this way, it would be a circular, and thus uninformative, account of 

justification. So the challenge that explanatory coherentism must meet is to give an account, 

without using the concept of justification, of what makes one explanation better than another. 

7.4.2 Reliability Coherentism: Let us move on to the second way in which the coherentist 

approach might be carried out. Recall what a subject’s justification for believing p is all about: 

possessing a link between the belief that p and the truth of p. Suppose the subject knows that the 

origin of her belief that p is reliable. So she knows that beliefs coming from this source tend to 

be true. Such knowledge would give her an excellent link between the belief and its truth. So we 

might say that the neighborhood beliefs which confer justification on (H) are the following: 

 (1) I am having a visual experience (E): the cap looks blue to me. 

 (3) Experiences like (E) are reliable. 

Call coherentism of this kind reliability coherentism. If you believe (1) and (3), you are in 

possession of a good reason for thinking that the cap is indeed blue. So you are in possession of a 

good reason for thinking that the belief in question, (H), is true. That’s why, according to 

reliability coherentism, you are justified in believing (H). 

Like explanatory coherentism, this view faces a circularity problem. If (H) receives its 

justification in part because you also believe (3), then, (3) itself must be justified. But where 

would your justification for (3) come from? One answer would be: from your memory of 

perceptual success in the past. You remember that your visual experiences have had a good track 

https://plato.stanford.edu/entries/epistemology/#exH
https://plato.stanford.edu/entries/epistemology/#exH
https://plato.stanford.edu/entries/epistemology/#exH


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record. They have rarely led you astray. The problem is that you cannot justifiably attribute a 

good track record to your perceptual faculties without using your perceptual faculties. So, if 

reliability coherentism is going to work, it would have to be legitimate to use a faculty for the 

very purpose of establishing the reliability of that faculty itself. But it is not clear that this is 

legitimate. 

Thus Richard Fumerton says the following, in the context of employing circular reasoning for 

the purpose of rebutting skepticism: 

You cannot use perception to justify the reliability of 

perception! You cannot use memory to justify the 

reliability of memory! You cannot use induction to justify 

the reliability of induction! Such attempts to respond to 

skeptic’s concerns involve blatant, indeed pathetic, 

circularity.105 

We have seen that explanatory coherentism and reliability coherentism each face its own 

distinctive circularity problem. Since both are versions of doxastic coherentism, they both face a 

further difficulty: Do people, under normal circumstances, really form beliefs like (1), (2), and 

(3)? It would seem they do not. It could be objected, therefore, that these two versions of 

coherentism make excessive intellectual demands of ordinary subjects who are unlikely to have 

the background beliefs that, according to these versions of coherentism, are needed for 

justification. This objection could be avoided by stripping coherentism of its doxastic element. 

The result would be the following version of coherentism, which results from the rejection of 

epistemic basicality (the epistemic conception of basicality). 

7.4.3 Dependence Coherentism: Whenever one is justified in believing a proposition p1, one’s 

justification for believing p1 depends on justification one has for believing some further 

propositions, p1, p2, … pn. 

An explanatory coherentist might say that, for you to be justified in believing (H), it is not 

necessary that you actually believe (1) and (2). However, it is necessary that you 

have justification for believing (1) and (2). It is your having justification for (1) and (2) that gives 

you justification for believing (H). A reliability coherentist might make an analogous point. He 

might say that, to be justified in believing (H), you need not believe anything about the reliability 

of the origin of your belief. You must, however, have justification for believing that the origin of 

your belief is reliable; that is, you must have justification for (1) and (3). Both versions of 

dependence coherentism, then, rest on the supposition that it is possible to have justification for a 

proposition without actually believing that proposition.  

Dependence coherentism is a significant departure from the way coherentism has typically been 

construed by its advocates. According to the typical construal of coherentism, a belief is 

                                                             
105 R.A. Fumerton, Metaepistemology and Skepticism, 177. 

https://plato.stanford.edu/entries/epistemology/#exH
https://plato.stanford.edu/entries/epistemology/#ex1
https://plato.stanford.edu/entries/epistemology/#ex1
https://plato.stanford.edu/entries/epistemology/#ex3


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justified, only if the subject has certain further beliefs that constitute reasons for the given belief. 

Dependence coherentism rejects this. According to it, justification need not come in the form of 

beliefs. It can come in the form of introspective and memorial experience, so long as such 

experience gives a subject justification for beliefs about either reliability or explanatory 

coherence. In fact, dependence coherentism allows for the possibility that a belief is justified, not 

by receiving any of its justification from other beliefs, but solely by suitable perceptual 

experiences and memory experience.106 

Next, let us examine some of the reasons provided in the debate over foundationalism and 

coherentism.  

7.5 Why Foundationalism? 

7.5.1 The Regress Argument 

The regress problem (also known as Agrippa’s Trilemma) is the problem of providing a 

complete logical foundation for human knowledge. The traditional way of supporting a rational 

argument is to appeal to other rational arguments, typically using chains of reason and rules of 

logic. A classic example that goes back to Aristotle is deducing that Socrates is mortal. We have 

a logical rule that says All humans are mortal and an assertion that Socrates is human and we 

deduce that Socrates is mortal. In this example how do we know that Socrates is human? 

Presumably we apply other rules such as: All born from human females are human. Which then 

leaves open the question how do we know that all born from humans are human? This is the 

regress problem: how can we eventually terminate a logical argument with some statements that 

do not require further justification but can still be considered rational and justified? As John 

Pollock stated: 

...to justify a belief one must appeal to a further justified 

belief. This means that one of two things can be the case. 

Either there are some beliefs that we can be justified for 

holding, without being able to justify them on the basis of 

any other belief, or else for each justified belief there is an 

infinite regress of (potential) justification [the nebula 

theory]. On this theory there is no rock bottom of 

justification. Justification just meanders in and out through 

our network of beliefs, stopping nowhere.107 

The apparent impossibility of completing an infinite chain of reasoning is thought by some to 

support skepticism. It is also the impetus for Descartes’ famous dictum: I think, therefore I am. 

                                                             
106 Cf. S. Haack, Evidence and Inquiry: Towards Reconstruction in Epistemology (Oxford: Blackwell, 1993), 21. 
107 Cf. Peter Klein, “Skepticism,” in Zalta, Edward N. (ed.), The Stanford Encyclopedia of Philosophy (2015). 
Retrieved 30 October, 2021. 

https://en.wikipedia.org/wiki/Regress_argument
https://en.wikipedia.org/wiki/Agrippa%27s_Trilemma
https://en.wikipedia.org/wiki/Skepticism
https://en.wikipedia.org/wiki/I_think,_therefore_I_am
https://plato.stanford.edu/archives/sum2015/entries/skepticism/


55 
 

Descartes was looking for some logical statement that could be true without appeal to other 

statements. 

Now, the main argument for foundationalism is called the regress argument. It is an argument 

from elimination. With regard to every justified belief, B1, the question arises where does the 

justification of B1 comes from. If B1 is not basic, it would have to come from another belief, B2. 

But B2 can justify B1 only if B2 is justified itself. If B2 is basic, the justificatory chain would end 

with B2. But if B2 is not basic, we need a further belief, B3. If B3 is not basic, we need a fourth 

belief, and so forth. Unless the ensuing regress terminates in a basic belief, we get two 

possibilities: the regress will either return back to B1 or continue ad infinitum. According to the 

regress argument, both of these possibilities are unacceptable. Therefore, if there are justified 

beliefs, there must be basic beliefs. 

Steup noted that this argument suffers from various weaknesses.108 First, we may wonder 

whether the alternatives to foundationalism are really unacceptable. In the recent literature on 

this subject, we actually find an elaborate defense of the position that infinitism is the correct 

solution to the regress problem. Nor should circularity be dismissed too quickly. The issue is not 

whether a simple argument of the form p therefore p can justify the belief that p. Of course it 

cannot. Rather, the issue is ultimately whether, in the attempt to show that trust in our faculties is 

reasonable, we may make use of the input our faculties deliver. Whether such circularity is as 

unacceptable as a p-therefore-p inference is an open question.109 

Moreover, the avoidance of circularity does not come cheap. Experiential foundationalists claim 

that perception is a source of justification. Hence they need to answer the J-question: Why is 

perception a source of justification? As we saw above, if we wish to answer this question without 

committing ourselves to the kind of circularity dependence coherentism involves, we must 

choose between externalism and an appeal to brute necessity. 

The second weakness of the regress argument is that its conclusion merely says this: If there are 

justified beliefs, there must be justified beliefs that do not receive their justification from other 

beliefs. Its conclusion does not say that, if there are justified beliefs, there must be beliefs whose 

justification is independent of any justification for further beliefs. So the regress argument, if it 

were sound, would merely show that there must be doxastic basicality. Dependence coherentism, 

however, allows for doxastic basicality. So the regress argument merely defends experiential 

foundationalism against doxastic coherentism. It does not tell us why we should prefer 

experiential foundationalism to dependence coherentism. 

Experiential foundationalism can be supported by citing cases like the blue cap example. Such 

examples make it plausible to assume that perceptual experiences are a source of justification. 

But they do not arbitrate between dependence coherentism and experiential foundationalism, 

                                                             
108 M. steup and Ram Nata, “Epistemology.” 
109 Ibid. 

https://plato.stanford.edu/entries/epistemology/#jquestion


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since both of those views appeal to perceptual experiences to explain why perceptual beliefs are 

justified. 

Lastly, foundationalism can be supported by advancing objections to coherentism. One 

prominent objection is that coherentism somehow fails to ensure that a justified belief system is 

in contact with reality. This objection derives its force from the fact that fiction can be perfectly 

coherent. Why think, therefore, that the coherence of a belief system is a reason for thinking that 

the beliefs in that system tend to be true? Coherentists could respond to this objection by saying 

that, if a belief system contains beliefs such as “Many of my beliefs have their origin in 

perceptual experiences” and “My perceptual experiences are reliable”, it is reasonable for the 

subject to think that his belief system brings her into contact with external reality. 

This looks like an effective response to the no-contact-with-reality objection. Moreover, it is not 

easy to see why foundationalism itself should be better positioned than coherentism when 

contact with reality is the issue. What is meant by “ensuring” contact with reality? If 

foundationalists expect a logical guarantee of such contact, basic beliefs must be infallible. That 

would make contact with reality a rather expensive commodity. Given its price, foundationalists 

might want to lower their expectations. According to an alternative construal, we expect merely 

the likelihood of contact with reality. But if coherentists account for the epistemic value of 

perception in any way, then they can meet that expectation as well as foundationalists can. 

Since coherentism can be construed in different ways, it is unlikely that there is one single 

objection that succeeds in refuting all possible versions of coherentism. Doxastic coherentism, 

however, seems particularly vulnerable to criticism coming from the foundationalist camp. We 

have already considered one of these: It would seem that doxastic coherentism makes excessive 

intellectual demands on believers. When dealing with the mundane tasks of everyday life, we do 

not normally bother to form beliefs about the explanatory coherence of our beliefs or the 

reliability of our belief sources. 

According to a second objection, doxastic coherentism fails by being insensitive to the epistemic 

relevance of perceptual experiences. Foundationalists could argue as follows. Suppose you are 

observing a chameleon that rapidly changes its colors. A moment ago it was blue, now it is 

purple. You still believe it is blue. Your belief is now unjustified because you believe the 

chameleon is blue even though it looks purple to you. Then the chameleon changes its color back 

to blue. Now your belief that the chameleon is blue is justified again because the chameleon once 

again looks blue to you. The point would be that what is responsible for the changing 

justificatory status of your belief is solely the way the chameleon looks to you. Since doxastic 

coherentism does not attribute epistemic relevance to perceptual experiences by themselves, it 

cannot explain why your belief is first justified, then unjustified, and eventually justified again. 

Doxastic coherentism might reply that, when the chameleon changes its color to purple, you 

form the belief that the chameleon looks purple to you. Because of this belief, you will not be 

justified in still believing that the chameleon is blue. Therefore, doxastic coherentism can explain 



57 
 

after all why your belief (the chameleon is blue) is unjustified after the chameleon changed its 

color to purple. The problem with this reply is that foundationalists are free to describe the 

example in whatever way they want (as long as it remains conceivable).110 And obviously, they 

would want to describe it by stipulating that you do not form any beliefs about how the 

chameleon appears to you. In response to that, doxastic coherentists could say that your failing to 

form beliefs about how the chameleon appears to you is inconceivable. That claim, however, 

does not recommend itself as a plausible one. 

7.5.2 Infinitism 

An alternative resolution to the regress problem is known as infinitism. Infinitists take the 

infinite series to be merely potential, in the sense that an individual may have indefinitely many 

reasons available to them, without having consciously thought through all of these reasons when 

the need arises. This position is motivated in part by the desire to avoid what is seen as the 

arbitrariness and circularity of its chief competitors, foundationalism and coherentism. The most 

prominent defense of infinitism has been given by Peter Klein.111 

7.6 Why Coherentism? 

Coherentism is typically defended by attacking foundationalism as a viable alternative. To argue 

against privilege foundationalism, coherentists pick an epistemic privilege they think is essential 

to foundationalism, and then argue that either no beliefs, or too few beliefs, enjoy such a 

privilege. Against experiential foundationalism, different objections have been advanced. One 

line of criticism is that perceptual experiences do not have propositional content. Therefore, the 

relation between a perceptual belief and the perceptual experience that gives rise to it can only be 

causal. But it is not clear that this is correct. When you see the cap and it looks blue to you, does 

your visual experience—its looking blue to you—not have the propositional content that the cap 

is blue? If it does, then why not allow that your perceptual experience can play a justificatory 

role? 

Another line of thought is that, if perceptual experiences have propositional content, they cannot 

stop the justificatory regress because they would then be in need of justification themselves. 

That, however, is a strange thought. In our actual epistemic practice, we never demand of others 

to justify the way things appear to them in their perceptual experiences. Indeed, such a demand 

would seem absurd. Suppose I ask you: “Why do you think that the cap is blue?” You answer: 

“Because it looks blue to me”. There are sensible further questions I might ask at that point. For 

instance, I might ask: “Why do you think its looking blue to you gives you a reason for believing 

it is blue?” Or I might ask: “Could you not be mistaken in believing it looks blue to you?” But 

now suppose I ask you: “Why do you suppose the perceptual experience in which the cap looks 

blue to you is justified?” In response to that question, you should accuse me of misusing the 

                                                             
110 Ibid. 
111 Peter D. Klein and John Turri, “Infinitism in Epistemology,” Internet Encyclopedia of Philosophy. Retrieved 30 
October, 2021. 

https://en.wikipedia.org/wiki/Infinitism
https://en.wikipedia.org/wiki/Peter_D._Klein
https://www.iep.utm.edu/inf-epis/


58 
 

word “justification”. I might as well ask you what it is that justifies your headache when you 

have one, or what justifies the itch in your nose when you have one. The latter questions, you 

should reply, would be as absurd as my request for stating a justifying reason for your perceptual 

experience. 112 

Experiential foundationalism, then, is not easily dislodged. On what grounds could coherentists 

object to it? To raise problems for experiential foundationalism, coherentists could press the J-

question: Why are perceptual experiences a source of justification? If foundationalists answer the 

J-question appealing to evidence that warrants the attribution of reliability to perceptual 

experiences, experiential foundationalism morphs into dependence coherentism. To avoid this 

outcome, foundationalists would have to give an alternative answer. One way of doing this 

would be to adopt the epistemic conception of basicality, and view it as a matter of necessity that 

perception is a source of justification. It remains to be seen whether such a view is sustainable. 

7.7 Foundherentism 

An intermediate position, known as foundherentism, is advanced by Susan Haack. 

Foundherentism is meant to unify foundationalism and coherentism. Haack explains the view by 

using a crossword puzzle as an analogy. Whereas, for example, infinitists regard the regress of 

reasons as taking the form of a single line that continues indefinitely, Haack has argued that 

chains of properly justified beliefs look more like a crossword puzzle, with various different 

lines mutually supporting each other.113 Thus, Haack’s view leaves room for both chains of 

beliefs that are vertical (terminating in foundational beliefs) and chains that are horizontal 

(deriving their justification from coherence with beliefs that are also members of foundationalist 

chains of belief). 

 

 

 

 

 

 

 

 

 

 

 

                                                             
112 Ibid. 
113 Nigel Warburton, Thinking from A to Z, 44. 

https://plato.stanford.edu/entries/epistemology/#jquestion
https://plato.stanford.edu/entries/epistemology/#jquestion
https://en.wikipedia.org/wiki/Foundherentism
https://en.wikipedia.org/wiki/Susan_Haack


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CHAPTER EIGHT 

SOURCES OF KNOWLEDGE AND JUSTIFICATION 

8.1 Introductory Discourse 

Beliefs arise in people for a wide variety of causes. Among them are psychological factors such 

as desires, emotional needs, prejudice, and biases of various kinds. Obviously, when beliefs 

originate in sources like these, they do not qualify as knowledge even if true. For true beliefs to 

count as knowledge, it is necessary that they originate in sources we have good reason to 

consider reliable. These are perception, introspection, memory, reason, and testimony. Let us 

briefly consider each of these. 

8.2 Perception 

Our perceptual faculties include at least our five senses: sight, touch, hearing, smelling, and 

tasting. We must distinguish between an experience that can be classified 

as perceiving that p (for example, seeing that there is tea in the cup and tasting that it is sweet), 

which entails that p is true, and a perceptual experience in which it seems to us as though p, but 

where p might be false. Let us refer to this latter kind of experience as perceptual seemings. The 

reason for making this distinction lies in the fact that perceptual experience is fallible. The world 

is not always as it appears to us in our perceptual experiences. We need, therefore, a way of 

referring to perceptual experiences in which p seems to be the case that allows for the possibility 

of p being false. That is the role assigned to perceptual seemings. So some perceptual seemings 

that p are cases of perceiving that p, others are not. When it looks to you as though there is a cup 

of tea on the table and in fact there is, the two states coincide. If, however, you hallucinate that 

there is a cup on the table, you have a perceptual seeming that p without perceiving that p. 

One family of epistemological issues about perception arises when we concern ourselves with 

the psychological nature of the perceptual processes through which we acquire knowledge of 

external objects. According to direct realism, we can acquire such knowledge because we can 

directly perceive such objects. For example, when you see a tomato on the table, what you 

perceive is the tomato itself. According to indirect realism, we acquire knowledge of external 

objects by virtue of perceiving something else, namely appearances or sense-data. An indirect 

realist would say that, when you see and thus know that there is a tomato on the table, what you 

really see is not the tomato itself but a tomato-like sense-datum or some such entity. 

Direct and indirect realists hold different views about the structure of perceptual knowledge. 

Indirect realists would say that we acquire perceptual knowledge of external objects by virtue of 

perceiving sense data that represent external objects. Sense data enjoy a special status: we know 

directly what they are like. Hence, indirect realists think that, when perceptual knowledge is 

foundational, it is knowledge of sense data and other mental states. Knowledge of external 

objects is indirect: derived from our knowledge of sense data. The basic idea is that we have 

indirect knowledge of the external world because we can have foundational knowledge of our 



60 
 

own mind. Direct realists, in contrast, say that perceptual experiences can give you direct, 

foundational knowledge of external objects. 

We take our perceptual faculties to be reliable. But how can we know that they are reliable? For 

externalists, this might not be much of a challenge. If the use of reliable faculties is sufficient for 

knowledge, and if by using reliable faculties we acquire the belief that our faculties are reliable, 

then we come to know that our faculties are reliable. But even externalists might wonder how 

they can, via argument, show that our perceptual faculties are reliable. The problem is this: it 

would seem the only way of acquiring knowledge about the reliability of our perceptual faculties 

is through memory, through remembering whether they served us well in the past. But should I 

trust my memory, and should I think that the episodes of perceptual success that I seem to recall 

were in fact episodes of perceptual success? If I am entitled to answer these questions with 

“yes”, then I need to have, to begin with, reason to view my memory and my perceptual 

experiences as reliable. It would seem, therefore, that there is no non-circular way of arguing for 

the reliability of one’s perceptual faculties.114 

8.3 Introspection 

Introspection is the capacity to inspect the present contents of one’s own mind. Through 

introspection, one knows what mental states one is currently in: whether one is thirsty, tired, 

excited, or depressed. Compared with perception, introspection appears to have a special status. 

It is easy to see how a perceptual seeming can go wrong: what looks like a cup of tea on the table 

might be just be a clever hologram that is visually indistinguishable from an actual cup of tea. 

But can it introspectively seem to me that I have a headache when in fact I do not? It is not easy 

to see how it could be. Thus introspection is widely thought to enjoy a special kind of immunity 

to error. But what does this amount to? 

First, it could be argued that, when it comes to introspection, there is no difference between 

appearance and reality; therefore, introspective seemings infallibly constitute their own success. 

Alternatively, one could view introspection as a source of certainty. Here the idea is that an 

introspective experience of p eliminates any possible reason for doubt as to whether p is true. 

Finally, one could attempt to explain the specialness of introspection by examining the way we 

respond to first-person reports: typically, a special authority is attributed a special authority to 

such reports. According to this approach, introspection is incorrigible: its deliverances cannot be 

corrected by any other source. 

However, we construe the special kind of immunity to error that introspection enjoys, such 

immunity is not enjoyed by perception. Some foundationalists have therefore thought that the 

foundations of our empirical knowledge can be furnished by introspection of our own perceptual 

experiences, rather than perception of mind-independent things around us. 

                                                             
114 W.P. Alston, “Varieties of Privileged Access”, 7ff. 



61 
 

Is it really true, however, that, compared with perception, introspection is in some way special? 

Critics of foundationalism have argued that introspection is not infallible. Might one not confuse 

an unpleasant itch for a pain? Might I not think that the shape before me appears circular to me 

when in fact it appears slightly elliptical to me? If it is indeed possible for introspection to 

mislead, then it is not clear in what sense introspection can constitute its own success, provide 

certainty, or even incorrigibility. Yet it is also not easy to see either how, if one clearly and 

distinctly feels a throbbing headache, one could be mistaken about that. Introspection, then, turns 

out to be a mysterious faculty. On the one hand, it does not seem to be an infallible faculty; on 

the other hand, it is not easy to see how error is possible in many specific cases of introspection. 

The definition of introspection as the capacity to know the present contents of one’s own mind 

leaves open the question of how similar the different exercises of this capacity may be from one 

another. According to some epistemologists, when we exercise this capacity with respect to our 

sensations, we are doing something very different from what we do when we exercise this 

capacity with respect to our own conscious beliefs, intentions, or other rationally evaluable states 

of mind: our exercises of this capacity with respect to our own conscious, rationally evaluable 

states of mind is, they claim, partly constitutive of our being in those very states. In support of 

this claim, they point out that we sometimes address questions of the form “do you believe 

that p?” by considering whether it is true that p, and reporting our belief concerning p not by 

inspecting our mind, but rather by making up our mind.115 

8.4 Memory 

Memory is the capacity to retain knowledge acquired in the past. What one remembers, though, 

need not be a past event. It may be a present fact, such as one’s telephone number, or a future 

event, such as the date of the next elections. Memory is, of course, fallible. Not every experience 

as of remembering that p is an instance of correctly remembering that p. We should distinguish, 

therefore, between remembering that p (which entails the truth of p) and seeming to remember 

that p (which does not entail the truth of p). 

What makes memorial seemings a source of justification? Is it a necessary truth that, if one has a 

memorial seeming that p, one has thereby prima facie justification for p? Or is memory a source 

of justification only if, as coherentists might say, one has reason to think that one’s memory is 

reliable? Or is memory a source of justification only if, as externalists would say, it is in fact 

reliable? Also, how can we respond to skepticism about knowledge of the past? Memorial 

seemings of the past do not guarantee that the past is what we take it to be. We think that we are 

older than twenty years, but it is very possible that we are not.  This applies to our dispositions to 

have memorial seemings of a more distant past and items, such as apparent fossils that suggest a 

past going back millions of years. Our seeming to remember these things does not entail, 

                                                             
115 R. Moran, Authority and Estrangement: An Essay on Self-Knowledge (Princeton, NJ: Princeton University Press, 
2002), 94. 



62 
 

therefore, that it really is. Why, then, should we think that memory is a source of knowledge 

about the past? 

 

 

8.5 Reason 

Some beliefs are (thought to be) justified independently of experience. Justification of that kind 

is said to be a priori. A standard way of defining a priori justification is as follows: 

8.5.1 A Priori Justification 

S is justified a priori in believing that p if and only if S’s justification for believing that p does 

not depend on any experience. 

When they are knowledgeably held, beliefs justified in this way are instances of a 

priori knowledge.  

What exactly counts as experience? If by “experience” we mean just perceptual experiences, 

justification deriving from introspective or memorial experiences would count as a priori. For 

example, I could then know a priori that I am thirsty, or what I ate for breakfast this morning. 

While the term “a priori” is sometimes used in this way, the strict use of the term restricts a 

priori justification to justification derived solely from the use of reason. According to this usage, 

the word “experiences” in the definition above includes perceptual, introspective, and memorial 

experiences alike. On this narrower understanding, paragons of what I can know a priori are 

conceptual truths (such as “All bachelors are unmarried”), and truths of mathematics, geometry 

and logic. 

Justification and knowledge that is not a priori is called “a posteriori” or “empirical”. For 

example, in the narrow sense of “a priori”, whether I am thirsty or not is something I know 

empirically (on the basis of introspective experiences), whereas I know a priori that 12 divided 

by 3 is 4. 

Several important issues arise about a priori knowledge. First, does it exist at all? Skeptics about 

apriority deny its existence. They do not mean to say that we have no knowledge of mathematics, 

geometry, logic, and conceptual truths. Rather, what they claim is that all such knowledge is 

empirical.116 

Second, if a priori justification is possible, exactly what does it involve? What makes a belief 

such as “All bachelors are unmarried” justified? Is it an unmediated grasp of the truth of this 

proposition? Or does it consist of grasping that the proposition is necessarily true? Or is it the 

purely intellectual state of “seeing” (with the “eye of reason”) or “intuiting” that this proposition 

                                                             
116 Ibid. 



63 
 

is true (or necessarily true)?117 Or is it, as externalists would suggest, the reliability of the 

cognitive process by which we come to recognize the truth of such a proposition? 

Third, if a priori knowledge exists, what is its extent? Empiricists have argued that a 

priori knowledge is limited to the realm of the analytic, consisting of propositions true solely by 

virtue of our concepts, and so do not convey any information about the world. Propositions that 

convey genuine information about world are called synthetic. A priori knowledge of synthetic 

propositions, empiricists would say, is not possible. Rationalists deny this. They might appeal to 

a proposition such as “If a ball is green all over, then it does not have black spots” as an example 

of a proposition that is both synthetic and yet knowable a priori.118 

8.6 Testimony 

Testimony differs from the sources we considered above because it is not distinguished by 

having its own cognitive faculty. Rather, to acquire knowledge of p through testimony is to come 

to know that p on the basis of someone’s saying that p. “Saying that p” must be understood 

broadly, as including ordinary utterances in daily life, postings by bloggers on their blogs, 

articles by journalists, books and writings by authors, sermons from preachers, lectures from our 

teachers, delivery of information on television, radio, tapes, books, and other media. So, when 

you ask the person next to you what time it is, and she tells you, and you thereby come to know 

what time it is, that is an example of coming to know something on the basis of testimony.  

The epistemological puzzle testimony raises is this: Why is testimony a source of knowledge? 

An externalist might say that testimony is a source of knowledge if, and because, it comes from a 

reliable source. But here, even more so than in the case of our faculties, internalists will not find 

that answer satisfactory. Suppose you hear someone saying “p”. Suppose, further, that person is 

in fact utterly reliable with regard to the question of whether p is the case or not. Finally, suppose 

you have no clue whatever as to that person’s reliability. Would it not be plausible to conclude 

that, since that person’s reliability is unknown to you, that person’s saying “p” does not put you 

in a position to know that p? But if the reliability of a testimonial source is not sufficient for 

making it a source of knowledge, what else is needed? 

Thomas Reid suggested that, by our very nature, we accept testimonial sources as reliable and 

tend to attribute credibility to them unless we encounter special contrary reasons.119 But that is 

merely a statement of the attitude we in fact take toward testimony. What is it that makes that 

attitude reasonable? It could be argued that, in one’s own personal experiences with testimonial 

sources, one has accumulated a long track record that can be taken as a sign of reliability. 

                                                             
117 J. Bengson, “The Intellectual Given”, Mind, 124(495), (2015), 707. 
118 B. Ichikawa, and Benjamin Jarvis, “Thought-Experiment Intuitions and Truth in Fiction”, Philosophical Studies, 
142(2), (2009), 221. 
119Derek R, Brookes (ed.), Thomas Reids’ An Inquiry into the Human Mind on the Principles of Common Sense 
(Pennsylvania: Pennsylvania State University Press, 1997. 



64 
 

However, when we think of the sheer breadth of the knowledge we derive from testimony, one 

wonders whether one’s personal experiences constitute an evidence base rich enough to justify 

the attribution of reliability to the totality of the testimonial sources one tends to trust.120 An 

alternative to the track record approach would be to declare it a necessary truth that trust in 

testimonial sources is at least prima facie justified. While this view has been prominently 

defended, it requires an explanation of what makes such trust necessarily prima facie justified. 

Such explanations have proven to be controversial.121 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                             
120 E. Fricker, “Against Gullibility”, in Knowing from Words: Western and Indian Philosophical Analysis of 
Understanding and Testimony, Bimal Krishna Matilal and Arindam Chakrabarti (eds.), (Dordrecht: Springer 
Netherlands, 1994), 126–127; M. Fricker, Epistemic Injustice: Power and the Ethics of Knowing (Oxford: Oxford 
University Press, 2002). 
121 Cf. J. Lackey, Learning from Words: Testimony as a Source of Knowledge (Oxford: Oxford University Press, 2008), 
119. 



65 
 

CHAPTER NINE 

PHILOSOPHICAL SKEPTICISM 

9.1 Introductory Discourse 

Epistemic skepticism questions whether knowledge is possible at all. Generally speaking, 

skeptics argue that knowledge requires certainty, and that most or all of our beliefs 

are fallible (meaning that our grounds for holding them always, or almost always, fall short of 

certainty), which would together entail that knowledge is always or almost always impossible for 

us. Characterizing knowledge as strong or weak is dependent on a person’s viewpoint and their 

characterization of knowledge. Much of modern epistemology is derived from attempts to better 

understand and address philosophical skepticism.  

9.2 Ancient Skepticism 

There were at least two kinds of ancient skepticism: academic skepticism and Pyrrhonism. The 

first, Academic Skepticism, arose in the Academy (the school founded by Plato) in the 3rd 

century BCE and was propounded by the Greek philosopher Arcesilaus (c. 315–c. 240 BCE), 

about whom Cicero (106–43 BCE), Sextus Empiricus (flourished 3rd century CE), and Diogenes 

Laërtius (flourished 3rd century CE) provide information.122 The Academic Skeptics, who are 

sometimes called “dogmatic” Skeptics, argued that nothing could be known with certainty. That 

form of Skepticism seems susceptible to the objection, raised by the Stoic Antipater 

(flourished c. 135 BCE) and others, that the view is self-contradictory.123 To know that 

knowledge is impossible is to know something. Hence, dogmatic Skepticism must be false. 

 

Carneades (c. 213–129 BCE), also a member of the Academy, developed a subtle reply to the 

charge. Academic Skepticism, he insisted, is not a theory about knowledge or the world but 

rather a kind of argumentative strategy. According to the strategy, the Skeptic does not try to 

prove that he knows nothing. Instead, he simply assumes that he knows nothing and defends that 

assumption against attack.124 The burden of proof, in other words, is on those who believe that 

knowledge is possible. 

Carneades’ interpretation of Academic Skepticism renders it very similar to the other major 

kind, Pyrrhonism, which takes its name from Pyrrhon of Elis (c. 365–275 BCE). Pyrrhonists, 

while not asserting or denying anything, attempted to show that one ought to suspend judgment 

and avoid making any knowledge claims at all, even the negative claim that nothing is known.125 

The Pyrrhonist’s strategy was to show that for every proposition supported by some evidence, 

there is an opposite proposition supported by evidence that is equally good. Such arguments, 

which are designed to refute both sides of an issue, are known as “tropes.” The judgment that a 

tower is round when seen at a distance, for example, is contradicted by the judgment that the 

                                                             
122A.H. Armstrong. An Introduction to Ancient Philosophy (Methuen: London University, 1965), 32-33. 
123 Ibid. 
124 Ibid. 
125 Ibid. 

https://en.wikipedia.org/wiki/Philosophical_skepticism
https://en.wikipedia.org/wiki/Certainty
https://en.wikipedia.org/wiki/Fallibilism
https://en.wikipedia.org/wiki/Acatalepsy
https://www.britannica.com/topic/Academy-ancient-academy-Athens-Greece
https://www.britannica.com/biography/Arcesilaus
https://www.britannica.com/biography/Cicero
https://www.britannica.com/biography/Sextus-Empiricus
https://www.britannica.com/biography/Diogenes-Laertius
https://www.britannica.com/biography/Diogenes-Laertius
https://www.merriam-webster.com/dictionary/Skepticism
https://www.merriam-webster.com/dictionary/Stoic
https://www.merriam-webster.com/dictionary/dogmatic
https://www.britannica.com/biography/Carneades
https://www.britannica.com/topic/evidence-law
https://www.britannica.com/topic/Pyrrhonism
https://www.britannica.com/biography/Pyrrhon-of-Elis
https://www.britannica.com/topic/trope-philosophy


66 
 

tower is square when seen up close. The judgment that Providence cares for all things, which is 

supported by the orderliness of the heavenly bodies, is contradicted by the judgment that many 

good people suffer misery and many bad people enjoy happiness. The judgment that apples have 

many properties—shape, colour, taste, and aroma—each of which affects a sense organ, is 

contradicted by the equally good possibility that apples have only one property that affects each 

sense organ differently. 

What is at stake in such arguments is “the problem of the criterion” – that is, the problem of 

determining a justifiable standard against which to measure the worth or validity of judgments, 

or claims to knowledge. According to the Pyrrhonists, every possible criterion is either 

groundless or inconclusive. Thus, suppose that something is offered as a criterion. The 

Pyrrhonist will ask what justification there is for it. If no justification is offered, then the criterion 

is groundless. If, on the other hand, a justification is produced, then the justification itself is 

either justified or it is not. If it is not justified, then again the criterion is groundless. If it is 

justified, then there must be some criterion that justifies it. But this is just what the dogmatist 

was supposed to have provided in the first place. 

If the Pyrrhonist needed to make judgments in order to survive, he would be in trouble. In fact, 

however, there is a way of living that bypasses judgment. One can live quite nicely, according to 

Sextus, by following custom and accepting things as they appear. In doing so, one does not judge 

the correctness of anything but merely accepts appearances for what they are.126 

Ancient Pyrrhonism is not strictly an epistemology, since it has no theory of knowledge and is 

content to undermine the dogmatic epistemologies of others, 

especially Stoicism and Epicureanism. Pyrrho himself was said to have had ethical motives for 

attacking dogmatists: being reconciled to not knowing anything, Pyrrho thought, induced 

serenity (ataraxia).127 

9.3 Kinds of Skepticism 

Much of modern epistemology aims to address one or another kind of skepticism. Skepticism is a 

challenge to our pre-philosophical conception of ourselves as cognitively successful or epistemic 

beings. Such challenges come in many varieties. One way in which these varieties differ, 

concerns the different kinds of cognitive success that they target: skepticism can challenge our 

claims to know, or our claims to believe justifiably, or our claims to have justification for 

believing, or our claims to have any good reasons for belief whatsoever. But another way in 

which these varieties differ is in whether the skepticism in question is fully general—targeting 

the possibility of enjoying any instance of the relevant cognitive success—or is selective—

targeting the possibility of enjoying the relevant cognitive success concerning a particular subject 

                                                             
126 Ibid. 
127 Ibid.  

https://www.merriam-webster.com/dictionary/criterion
https://www.britannica.com/topic/Stoicism
https://www.britannica.com/topic/Epicureanism
https://www.merriam-webster.com/dictionary/ethical
https://www.merriam-webster.com/dictionary/reconciled


67 
 

matter (e.g., the past, the minds of others, the world beyond our own consciousness), or 

concerning beliefs formed by a particular method (e.g., perception, memory, reasoning, etc.). 

9.3.1 Extreme/Mild Skepticism 

Epistemological skepticism can be classified as either mitigated/extreme or unmitigated/mild 

skepticism. Mitigated skepticism rejects strong or strict knowledge claims but does approve 

weaker ones, which can be considered virtual knowledge, but only with regard to justified 

beliefs. Unmitigated skepticism rejects claims of both virtual and strong 

knowledge.128 Characterizing knowledge as strong, weak, virtual or genuine can be determined 

differently depending on a person’s viewpoint as well as their characterization of knowledge.129  

9.3.2 Pyrrhonism 

One of the oldest forms of epistemic skepticism can be found in Agrippa’s trilemma (named 

after the Pyrrhonist philosopher Agrippa the Skeptic) which demonstrates that certainty cannot 

be achieved with regard to beliefs.130 Pyrrhonism dates back to Pyrrho of Elis from the 4th 

century BCE, although most of what we know about Pyrrhonism today is from the surviving 

works of Sextus Empiricus.131 Pyrrhonists claim that for any argument for a non-evident 

proposition, an equally convincing argument for a contradictory proposition can be produced. 

Pyrrhonists do not dogmatically deny the possibility of knowledge, but instead point out that 

beliefs about non-evident matters cannot be substantiated. 

9.3.3 Cartesian Skepticism 

The Cartesian evil demon problem, first raised by René Descartes, supposes that our sensory 

impressions may be controlled by some external power rather than the result of ordinary 

veridical perception. In such a scenario, nothing we sense would actually exist, but would instead 

be mere illusion. As a result, we would never be able to know anything about the world, since we 

would be systematically deceived about everything. The conclusion often drawn from evil 

demon skepticism is that even if we are not completely deceived, all of the information provided 

by our senses is still compatible with skeptical scenarios in which we are completely deceived, 

and that we must therefore either be able to exclude the possibility of deception or else must 

deny the possibility of infallible knowledge (that is, knowledge which is completely certain) 

beyond our immediate sensory impressions.132 While the view that no beliefs are beyond doubt 

other than our immediate sensory impressions is often ascribed to Descartes, he in fact thought 

that we can exclude the possibility that we are systematically deceived, although his reasons for 

                                                             
128 Stathis Psillos and Martin Curd, The Routledge companion to philosophy of science (London: Routledge, 2010), 
133. 
129 Ibid. 
130 Cf. Richard Popkin, “Skepticism,” In Edwards, Paul (ed.), Encyclopedia of Philosophy Volume 7 (London: 
Macmillan, 1972), 449. 
131 Ibid. 
132 W. James, and G. Gunn, Pragmatism and other Essays, (New York: Penguin Books, 2000), 14. 

https://en.wikipedia.org/wiki/Agrippa%27s_trilemma
https://en.wikipedia.org/wiki/Pyrrhonism
https://en.wikipedia.org/wiki/Agrippa_the_Skeptic
https://en.wikipedia.org/wiki/Pyrrho_of_Elis
https://en.wikipedia.org/wiki/Sextus_Empiricus
https://en.wikipedia.org/wiki/Evil_demon
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes


68 
 

thinking this are based on a highly contentious ontological argument for the existence of a 

benevolent God who would not allow such deception to occur.133 

9.3.4 General Skepticism 

General skepticism is motivated by reasoning from some apparently conflicting features of the 

kind of cognitive success in question. For instance, a general skeptic might claim that 

justification requires a regress of justifiers, but then argue that this regress of justifiers cannot be 

contained in any finite mind—and thus, the skeptic might conclude, no finite being can be 

justified in believing anything. Alternatively a general skeptic might claim that knowledge 

requires certainty, and that nobody can be certain of something unless there is nothing of which 

he could be even more certain—thus, the skeptic might conclude, we can know virtually 

nothing.134 

9.3.5 Selective Skepticism  

Selective skepticism, in contrast, is typically motivated by appeal to one or another skeptical 

hypothesis. A skeptical hypothesis is a hypothesis according to which the facts that you claim to 

know (whether these facts concern the past, or the mind of others, or the mind-independent 

world, or what have you) may, for all you can tell, be radically different from how they appear to 

you to be. Thus, a skeptical hypothesis is a hypothesis that distinguishes between the way things 

appear to you, on the one hand, and the way they really are, on the other; and this distinction is 

deployed in such a way as to pose a challenge to your cognitive success concerning the latter. 

Here are some examples of skeptical hypotheses:135 

i. All the other humans around me are automata who simply act exactly as if they have thoughts 

and feelings. 

ii. The whole universe was created no more than 5 minutes ago, replete with fake memories and 

other misleading evidence concerning a distant past. 

iii. I am lying in my bed dreaming everything that I am aware of right now. 

iv. I am a mere brain-in-a-vat (a BIV, for short) being electrochemically stimulated to have all 

these states of mind that I am now having. 

Skeptics can make use of such hypotheses in constructing various arguments that challenge our 

pre-philosophical picture of ourselves as cognitively successful. Consider, for instance, the BIV 

hypothesis, and some ways in which this hypothesis can be employed in a skeptical argument. 

                                                             
133 Ibid. 
134 P. Unger, Ignorance: A Case for Scepticism (Oxford: Oxford University Press, 1975), 100. 
135 M. Steup, Ernest Sosa (eds.), Contemporary Debates in Epistemology (Malden, MA: Blackwell, 2005), 117. 

https://en.wikipedia.org/wiki/Ontological_argument


69 
 

Here is one way of doing so. According to the BIV hypothesis, the experiences you would have 

as a BIV and the experiences you have as a normal person are perfectly alike, indistinguishable, 

so to speak, “from the inside”. Thus, although it appears to you as if you are a normally 

embodied human being, everything would appear exactly the same way to a BIV. Thus, the way 

things appear to you cannot provide you with knowledge that you are not a BIV. But if the way 

things appear to you cannot provide you with such knowledge, then nothing can give you such 

knowledge, and so you cannot know that you are not a BIV. Of course, you already know this 

much: if you are a BIV, then you do not have any hands. If you do not know that you are not a 

BIV, then you do not know that you are not in a situation in which you do not have any hands. 

But if you do not know that you are not in a situation in which you do not have any hands, then 

you do not know that you are not handless. And to not know that you are not handless is simply 

to not know that you have hands.136 We can summarize this skeptical argument as follows: 

9.4 The BIV-Knowledge Closure Argument 

 (C1) I don’t know that I’m not a BIV. 

 (C2) If I don’t know that I’m not a BIV, then I don’t know that I have hands. 

 Therefore: (C3) I don’t know that I have hands. 

As we have just seen, (C1) and (C2) are very plausible premises. It would seem, therefore, that 

the argument is sound. If it is, we must conclude we don’t know we have hands. But surely that 

conclusion cannot be right: if it turns out that I don’t know that I have hands, that must be 

because of something very peculiar about my cognitive relation to the issue of whether I have 

hands—not because of the completely anodyne considerations mentioned in the above argument. 

So we are confronted with a difficult challenge: The conclusion of the above argument seems 

plainly false, but on what grounds can we reject it? 

Here are some other ways of using the BIV-knowledge closure argument hypothesis to generate 

a skeptical argument. 

9.5 Responses to the Closure Argument 

Next, we will examine various responses to this argument. According to the first, we can see 

that (C2) is false if we distinguish between relevant and irrelevant alternatives. An alternative to 

a proposition p is any proposition that is incompatible with p. Your having hands and your being 

a BIV are alternatives: if the former is true, the latter is false, and vice versa. According to the 

thought that motivates the second premise of the BIV argument, you know that you have hands 

only if you can discriminate between your actually having hands and the alternative of being a 

(handless) BIV. But, by hypothesis, you cannot discriminate between these. That is why you 

don’t know that you have hands. 

                                                             
136Ibid. 

https://plato.stanford.edu/entries/epistemology/#closure2


70 
 

In response to such reasoning, a relevant alternatives theorist would say that your inability to 

discriminate between these two is not an obstacle to your knowing that you have hands, and that 

is because your being a BIV is not a relevant alternative to your having hands. What would be a 

relevant alternative? This, for example: your arms ending in stumps rather than hands, or your 

having hooks instead of hands, or your having prosthetic hands. But these alternatives do not 

prevent you from knowing that you have hands—not because they are irrelevant, but rather 

because you can discriminate between these alternatives and your having hands. The relevant 

alternative theorist holds, therefore, that you do know that you have hands: you know it because 

you can discriminate it from relevant alternatives, like your having stumps rather than hands. 

Thus, according to Relevant Alternatives theorists, you know that you have hands even though 

you don’t know that you are not a BIV. There are two chief problems for this approach. The first 

is that denouncing the BIV alternative as irrelevant is ad hoc unless it is supplemented with a 

principled account of what makes one alternative relevant and another irrelevant. The second is 

that premise 2 is highly plausible. To deny it is to allow that the following conjunction can be 

true: 

9.5.1 Abominable Conjunction: I know that I have hands but I do not know that I am not a 

(handless) BIV. 

Many epistemologists would agree that this conjunction is indeed abominable because it 

blatantly violates the basic and extremely plausible intuition that you cannot know you have 

hands without knowing that you are not a BIV. 

Next, let us consider a response to this “Closure Argument” according to which it is not the 

second but the first premise that must be rejected. G. E. Moore has pointed out that an argument 

succeeds only to the extent that its premises are more plausible than the conclusion.137 So if we 

encounter an argument whose conclusion we find much more implausible than the denial of the 

premises, then we can turn the argument on its head. According to this approach, we can respond 

to the BIV argument as follows:   

9.6 Counter BIV 

 (~C3) I know that I have hands. 

 (C2) If I don’t know that I’m not a BIV, then I don’t know that I have hands. 

 Therefore: (~C1) I know that I am not a BIV. 

Unless we are skeptics or opponents of closure, we would have to concede that this argument is 

sound. It is valid, and its premises are true. Yet few philosophers would agree that Counter BIV 

amounts to a satisfying response to the BIV argument. It fails to explain how one can know that 

one is not a BIV. The observation that the premises of the BIV argument are less plausible than 

the denial of its conclusion does not help us understand how such knowledge is possible. That is 

                                                             
137 G.E. Moore, “Proof of an External World”, Proceedings of the British Academy, (1959), 126. 



71 
 

why the Moorean response, unsupplemented with an account of how one can know that one is 

not a BIV, is widely thought to be an unsuccessful rebuttal of the Closure Argument.138 

We have looked at two responses to BIV-Knowledge Closure Argument. The relevant 

alternatives response implausibly denies the second premise. The Moorean response denies the 

first premise without explaining how we could possibly have the knowledge that the first premise 

claims we don’t have. Another prominent response, contextualism, avoids both of these 

objections. 

According to the contextualist, the precise contribution that the verb “to know” makes to the 

truth-conditions of the sentences in which it occurs varies from one context to another: in 

contexts in which the BIV hypothesis is under discussion, an agent counts as “knowing” a fact 

only if he can satisfy some extremely high (typically unachievable) epistemic feat, and this is 

why (1) is true. But in contexts in which the BIV hypothesis is not under discussion, an agent can 

count as “knowing” a fact even if his epistemic position vis-à-vis that fact is much more modest, 

and this is why (3), taken in isolation, appears false. 

The contextualist literature has grown vastly over the past two decades: different contextualists 

have different accounts of how features of context affect the meaning of some occurrence of the 

verb “to know”, and each proposal has encountered specific challenges concerning the semantic 

mechanisms that it posits, and the extent to which it explains the whole range of facts about 

which epistemic claims are plausible under which conditions.139 

9.7 The BIV-Justification Under-determination Argument 

 (U1) The way things appear to me could be equally well explained by the BIV-

knowledge closure argument hypothesis as by my ordinary beliefs that things appear to 

me the way they do because I perceive mind-independent objects. 

 (U2) If the way things appear to me could be equally well explained by either of two 

hypotheses, then I am not justified in believing one of those hypotheses rather than the 

other. 

 Therefore: (U3) I am not justified in believing that I perceive mind-independent objects. 

9.8 Responses to the Underdetermination Argument 

Both the contextualist and the Moorean responses, as discussed in the previous section, leave out 

one important detail. Both say that one can know that one is not a BIV (though contextualists 

grant this point only for the sense of “know” operational in low-standards contexts), but neither 

view explains how one can know such a thing. If, by hypothesis, a BIV has all the same states of 

mind that I have—including all the same perceptual experiences—then how can I be justified in 

                                                             
138 Ibid. 
139 Cf. S. Cohen, “Basic Knowledge and the Problem of Easy Knowledge”, 310. 



72 
 

believing that I am not a BIV? And if I cannot be justified in believing that I am not a BIV, then 

how can I know that I am not? 

Of course, the question about how I can be justified in believing that I am not a BIV is not 

especially hard for externalists to answer. From the point of view of an externalist, the fact that 

you and the BIV have the very same states of mind need not be at all relevant to the issue of 

whether you are justified in believing that you are not a BIV, since such justification is not fully 

determined by those mental states anyway. 

The philosophers who have had to do considerable work to answer the question how I can be 

justified in believing that I am not a BIV have typically done this work in reply to 

Underdetermination Argument. 

What might justify your belief that you are not a BIV? According to some philosophers, you are 

justified in believing that you are not a BIV because, for instance, you know perfectly well that 

current technology does not enable anyone to create a BIV. The proponent of the BIV hypothesis 

might regard this answer as no better than the Moorean response in the previous section: if you 

are allowed to appeal to (what you regard as your) knowledge of current technology to justify 

your belief that you are not a BIV, then why can’t the Moorean equally well rely on his 

knowledge that he has hands to justify his belief that he’s not a BIV? 

Philosophers who accept this objection, but who do not want to ground your justification for 

believing that you are not a BIV in purely externalistic factors, may instead claim that your belief 

is justified by the fact that your own beliefs about the external world provide a better explanation 

of your sense experiences than does the BIV hypothesis.140 

9.9 The BIV-Knowledge Defeasibility Argument 

 (D1) If I know that I have hands, then I know that any evidence indicating that I don’t 

have hands is misleading evidence. 

 (D2) If I know that some evidence is misleading, then I know that I should disregard that 

evidence. 

 Therefore: (D3) If I know that I have hands, then I know that I should disregard any 

evidence to the contrary. 

 (D4) I do not know that I should disregard any evidence to the contrary. 

 Therefore: (D5) I do not know that I have hands. 

9.10 Responses to the Defeasibility Argument 

The most influential reply to this argument is to say that, when I acquire evidence that I don’t 

have hands, such evidence makes me cease to know that I have hands. On this view, when I 

acquire such evidence, the argument above is sound. But prior to my acquiring such evidence, 

                                                             
140 B. Russell, The Problems of Philosophy (London: Williams & Norgate). 



73 
 

(4) is false, and so the argument above is not sound. Thus, the truth of (4), and consequently the 

soundness of this argument, depends on whether or not I have evidence that I don’t have hands. 

If I do have such evidence, then the argument is sound, but of course it has no general skeptical 

implications: all it shows is that I cannot know some fact whenever I have evidence that the fact 

does not obtain.141 

Plausible as this reply has seemed to most philosophers, it has been effectively challenged by 

Lasonen-Aarnio (2014b).142 Her argument is this: presumably, it is possible to have more than 

enough evidence to know some fact. But if it is possible to have more than enough evidence to 

know some fact, it follows that one might still know that fact even if one acquires some slight 

evidence against it. And yet, it would be wrong to leave one’s confidence entirely unaffected by 

the slight evidence that one acquires against that fact: though the evidence might be too slight to 

destroy one’s knowledge, it cannot be too slight to diminish one’s confidence even slightly. So 

long as one could continue to know a fact while rationally diminishing one’s confidence in it in 

response to new evidence, the most popular reply to the defeasibility argument fails. 

Other replies to the defeasibility argument include the denial of premise (2),143 the denial of 

(4),144 and the claim that the context-sensitivity of “knows” means that (4) is true only relative to 

contexts in which the possibility of future defeaters is relevant.145 But neither of these replies has 

yet received widespread assent. 

9.11 The BIV-Epistemic Possibility Argument 

 P1) It is at least possible that I am a BIV. 

 (P2) If it is possible that I am a BIV, then it is possible that I don’t have hands. 

 (P3) If it is possible that I don’t have hands, then I don’t know that I have hands. 

 Therefore: (P4) I don’t know that I have hands. 

Obviously, this list of skeptical arguments could be extended by varying either (a) the skeptical 

hypothesis employed, or (b) the kind of cognitive success being challenged, or (c) the 

epistemological principles that link the hypothesis in (a) and the challenge in (b). Some of the 

resulting skeptical arguments are more plausible than others, and some are historically more 

prominent than others, but we cannot undertake a comprehensive survey here. 

9.12 Responses to the Epistemic Possibility Argument 

The most common reply to this argument is either to deny premise (1), or to deny that we are 

justified in believing that premise (1) is true. Most writers would deny premise (1), and would do 

                                                             
141 G. Harman, Change in View, 3. 
142 M. Lasonen-Aarnio, “Higher-Order Evidence and the Limits of Defeat”, Philosophy and Phenomenological 
Research, 88(2), (2014a), 317. 
143 Ibid 
144Ibid. 
145 R. Neta, “S Knows That P”, Noûs, 36(4), (2002), 663. 



74 
 

so on whatever grounds they have for thinking that I can know that I am not a BIV: knowing that 

something is not the case excludes that thing’s being epistemically possible for you.146 

But a couple of influential writers—most notably Rogers Albritton and Thompson Clarke147 — 

do not claim that premise (1) is false. Rather, they deny that we are justified in believing that 

premise (1) is true. According to these writers, what normally justifies us in believing that 

something or other is epistemically possible is that we can conceive of discovering that it is true. 

For instance, what justifies me in believing, say, that it is possible that Mohammad Buhari has 

resigned is that I can clearly conceive of discovering that he has resigned. But if I attempt to 

conceive of discovering that I am a BIV, it is not clear that I can succeed in this attempt. I may 

conceive of coming upon some evidence that I am a BIV—but, insofar as this evidence tells in 

favor of the hypothesis that I am a BIV, does it not also undermine its own credibility? 

In such a case, is there anything at all that would count as “my evidence”? Without being able to 

answer this question in the affirmative, it is not clear that I can conceive of anything that would 

amount to discovering that I am a BIV. Of course, from the fact that I cannot conceive of 

anything that would amount to discovering that I am a BIV, it does not follow that I am not a 

BIV—and so it does not even follow that it is not possible that I am a BIV. But, whether or not 

it is possible that I am a BIV, I cannot be justified in thinking that it is. And that is to say that I 

cannot be justified in accepting premise (1) of this argument. 

 

 

 

 

 

 

 

 

 

 

 

                                                             
146 See K. DeRose, “Epistemic Possibilities”, The Philosophical Review, 100(4), (1991), 581–605, for an influential 
account of epistemic possibility that entails this view. 
147 R. Albritton, “On a Form of Skeptical Argument from Possibility”, Philosophical Issues, (2011), 21; and T. Clarke, 
“The Legacy of Skepticism”, The Journal of Philosophy, 69(20), (1972), 754–769. 



75 
 

CHAPTER TEN 

THE HISTORY OF EPISTEMOLOGY: ANCIENT AND MEDIEVAL PHILOSOPHIES 

 

10.1 Ancient Philosophy 

The central focus of ancient Greek philosophy was the problem of motion. Many pre-Socratic 

philosophers thought that no logically coherent account of motion and change could be given. 

Although the problem was primarily a concern of metaphysics, not epistemology, it had the 

consequence that all major Greek philosophers held that knowledge must not itself change or be 

changeable in any respect. That requirement motivated Parmenides (flourished 5th 

century BCE), for example, to hold that thinking is identical with “being” (i.e., all objects of 

thought exist and are unchanging) and that it is impossible to think of “nonbeing” or “becoming” 

in any way. 

 

10.1.1 Plato 

 

Plato accepted the Parmenidean constraint that knowledge must be unchanging. One 

consequence of that view, as Plato pointed out in the Theaetetus, is that sense experience cannot 

be a source of knowledge, because the objects apprehended through it are subject to change.148 

To the extent that humans have knowledge, they attain it by transcending sense experience in 

order to discover unchanging objects through the exercise of reason. 

The Platonic theory of knowledge thus contains two parts: first, an investigation into the nature 

of unchanging objects and, second, a discussion of how those objects can be known through 

reason. Of the many literary devices Plato used to illustrate his theory, the best known is 

the allegory of the cave, which appears in Book VII of the Republic. The allegory depicts people 

living in a cave, which represents the world of sense-experience. In the cave, people see only 

unreal objects, shadows, or images. Through a painful intellectual process, which involves the 

rejection and overcoming of the familiar sensible world, they begin an ascent out of the cave into 

reality. That process is the analogue of the exercise of reason, which allows one to apprehend 

unchanging objects and thus to acquire knowledge. The upward journey, which few people are 

able to complete, culminates in the direct vision of the Sun, which represents the source of 

knowledge. 

Plato’s investigation of unchanging objects begins with the observation that every faculty of the 

mind apprehends a unique set of objects: hearing apprehends sounds, sight apprehends visual 

images, and smell apprehends odours, and so on. Knowing also is a mental faculty, according to 

Plato, and therefore there must be a unique set of objects that it apprehends. Roughly speaking, 

those objects are the entities denoted by terms that can be used as predicates—e.g., “good,” 

                                                             
148 J.M. Cooper & D.S. Hutchinson, Plato’s Complete Works (London: Routledge, 1997). 

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“white,” and “triangle.”149 To say “This is a triangle,” for example, is to attribute a certain 

property, that of being a triangle, to a certain spatiotemporal object, such as a figure drawn in the 

sand. Plato is here distinguishing between specific triangles that are drawn, sketched, or painted 

and the common property they share, that of being triangular. Objects of the former kind, which 

he calls “particulars,” are always located somewhere in space and time—i.e., in the world 

of appearance. The property they share is a “form” or “idea” (though the latter term is not used in 

any psychological sense). Unlike particulars, forms do not exist in space and time; moreover, 

they do not change. They are thus the objects that one apprehends when one has knowledge. 

Reason is used to discover unchanging forms through the method of dialectic, which Plato 

inherited from his teacher Socrates. The method involves a process of question and answer 

designed to elicit a “real definition.” By a real definition Plato means a set of necessary and 

sufficient conditions that exactly determine the entities to which a given concept applies. The 

entities to which the concept “being a brother” applies, for example, are determined by the 

concepts “being male” and “being a sibling”: it is both necessary and sufficient for a person to be 

a brother that he be male and a sibling. Anyone who grasps these conditions understands 

precisely what being a brother is. 

In the Republic, Plato applies the dialectical method to the concept of justice. In response to a 

proposal by Cephalus that “justice” means the same as “honesty in word and deed,” Socrates 

points out that, under some conditions, it is just not to tell the truth or to repay debts.150 Suppose 

one borrows a weapon from a person who later loses his sanity. If the person then demands his 

weapon back in order to kill someone who is innocent, it would be just to lie to him, stating that 

one no longer had the weapon. Therefore, “justice” cannot mean the same as “honesty in word 

and deed.” By the technique of proposing one definition after another and subjecting each to 

possible counterexamples, Socrates attempts to discover a definition that cannot be refuted. In 

doing so he apprehends the form of justice, the common feature that all just things share. 

Plato’s search for definitions and, thereby, forms is a search for knowledge. But how should 

knowledge in general be defined? In the Theaetetus Plato argues that, at a minimum, knowledge 

involves true belief. No one can know what is false. People may believe that they know 

something that is in fact false. But in that case they do not really know; they only think they 

know. Knowledge is more than simply true belief. Suppose that someone has a dream in April 

that there will be an earthquake in September and, on the basis of that dream, forms the belief 

that there will be an earthquake in September. Suppose also that in fact there is an earthquake in 

September. The person has a true belief about the earthquake but not knowledge of it. What the 

person lacks is a good reason to support that true belief. In a word, the person lacks justification. 

Using such arguments, Plato contends that knowledge is justified true belief. 

                                                             
149 Ibid. 
150 Ibid. 

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Although there has been much disagreement about the nature of justification, the Platonic 

definition of knowledge was widely accepted until the mid-20th century, when the American 

philosopher Edmund L. Gettier produced a startling counterexample.151 Suppose that Kathy 

knows Oscar very well. Kathy is walking across the mall, and Oscar is walking behind her, out 

of sight. In front of her, Kathy sees someone walking toward her who looks exactly like Oscar. 

Unbeknownst to her, however, it is Oscar’s twin brother. Kathy forms the belief that Oscar is 

walking across the mall. Her belief is true, because Oscar is in fact walking across the mall 

(though she does not see him doing it). And her true belief seems to be justified, because 

the evidence she has for it is the same as the evidence she would have had if the person she had 

seen were really Oscar and not Oscar’s twin. In other words, if her belief that Oscar is walking 

across the mall is justified when the person she sees is Oscar, then it also must be justified when 

the person she sees is Oscar’s twin, because in both cases the evidence—the sight of an Oscar-

like figure walking across the mall—is the same. Nonetheless, Kathy does not know that Oscar is 

walking across the mall. According to Gettier, the problem is that Kathy’s belief is not causally 

connected to its object (Oscar) in the right way. 

 

10.1.2 Aristotle 

 

In the Posterior Analytics, Aristotle (384–322 BCE) claims that each science consists of a set of 

first principles, which are necessarily true and knowable directly, and a set of truths, which are 

both logically derivable from and causally explained by the first principles.152 

The demonstration of a scientific truth is accomplished by means of a series of syllogisms—a 

form of argument invented by Aristotle—in which the premises of each syllogism in the series 

are justified as the conclusions of earlier syllogisms. In each syllogism, the premises not only 

logically necessitate the conclusion (that is., the truth of the premises makes it logically 

impossible for the conclusion to be false) but causally explain it as well. Thus, in the syllogism:  

All stars are distant objects. All distant objects twinkle; Therefore, all stars twinkle, the fact that 

stars twinkle is explained by the fact that all distant objects twinkle and the fact that stars are 

distant objects. The premises of the first syllogism in the series are first principles, which do not 

require demonstration, and the conclusion of the final syllogism is the scientific truth in question.  

 

In an enigmatic passage, Aristotle claims that “actual knowledge is identical with its object.”153 

By that he seems to mean something like the following. When people learn something, they 

“acquire” it in some sense. What they acquire must be either different from the thing they know 

or identical with it. If it is different, then there is a discrepancy between what they have in mind 

and the object of their knowledge. But such a discrepancy seems to be incompatible with the 

                                                             
151Edmund Gettier, “Is Justified True Belief Knowledge?” Analysis, 23(6), 1963. 
152 https://www.britannica.com/topic/posterior-analytics 
153 Ibid.  

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existence of knowledge, for knowledge, which must be true and accurate, cannot deviate from its 

object in any way. One cannot know that blue is a colour, for example, if the object of that 

knowledge is something other than that blue is a colour. That idea, that knowledge is identical 

with its object, is dimly reflected in the modern formula for expressing one of the necessary 

conditions of knowledge: S knows that p only if it is true that p. 

To assert that knowledge and its object must be identical raises a question: In what way is 

knowledge “in” a person? Suppose that Smith knows what dogs are, that is, he knows what it is 

to be a dog. Then, in some sense, dogs, or being a dog, must be in the mind of Smith. But how 

can that be? Aristotle derives his answer from his general theory of reality.154 According to him, 

all (terrestrial) substances are composed of two principles: form and matter. All dogs, for 

example, consist of a form—the form of being a dog—and matter, which is the stuff out of 

which they are made. The form of an object makes it the kind of thing it is. Matter, on the other 

hand, is literally unintelligible. Consequently, what is in the knower when he knows what dogs 

are is just the form of being a dog. 

In his sketchy account of the process of thinking in De anima (On the Soul), Aristotle says that 

the intellect, like everything else, must have two parts: something analogous to matter and 

something analogous to form.155 The first is the passive intellect, the second the active intellect, 

of which Aristotle speaks tersely. “Intellect in this sense is separable, impassible, unmixed, since 

it is in its essential nature activity. When intellect is set free from its present conditions, it 

appears as just what it is and nothing more: it alone is immortal and eternal, and without it 

nothing thinks.”156 

The foregoing part of Aristotle’s views about knowledge is an extension of what he says about 

sensation. According to him, sensation occurs when the sense organ is stimulated by the sense 

object, typically through some medium, such as light for vision and air for hearing. That 

stimulation causes a “sensible species” to be generated in the sense organ itself. The “species” is 

some sort of representation of the object sensed. As Aristotle describes the process, the sense 

organ receives “the form of sensible objects without the matter, just as the wax receives the 

impression of the signet-ring without the iron or the gold.”157 After the death of Aristotle, the 

next major thing in the history of epistemology was the rise of skepticism, of which we have 

already devoted a chapter. 

 

10.1.3 St. Augustine 

 

                                                             
154 Ibid. 
155 https://www.britannica.com/topic/on-the-soul-by-aristotle/ 
156 Ibid. 
157 Ibid. 

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St. Augustine of Hippo (354–430) claimed that human knowledge would be impossible 

if God did not “illumine” the human mind and thereby allow it to see, grasp, or 

understand ideas.158 Ideas as Augustine construed them are—like Plato’s—timeless, immutable, 

and accessible only to the mind. They are indeed in some mysterious way a part of God and seen 

in God. Illumination, the other element of the theory, was for Augustine and his many followers, 

at least through the 14th century, a technical notion, built upon a visual metaphor. According to 

that view, the human mind is like an eye that can see when and only when God, the source of 

light, illumines it. Varying his metaphor, Augustine sometimes says that the human mind 

“participates” in God and even, that Christ illumines the mind by dwelling in it.159 It is important 

to emphasize that Augustine’s theory of illumination concerns all knowledge, not specifically 

mystical or spiritual knowledge. 

 

Before he articulated the theory in his mature years, soon after his conversion to Christianity, 

Augustine was concerned to refute the Skepticism of the Academy. In Against the 

Academicians (386) he claimed that, if nothing else, humans know disjunctive tautologies such 

as “Either there is one world or there is not one world” and “Either the world is finite or it is 

infinite.” Humans also know many propositions that begin with the phrase “It appears to me 

that,” such as “It appears to me that what I perceive is made up of earth and sky, or what appears 

to be earth and sky.” Furthermore, humans know logical (or what Augustine calls “dialectical”) 

propositions—for example, “If there are four elements in the world, there are not five,” “If there 

is one sun, there are not two,” “One and the same soul cannot die and still be immortal,” and 

“Man cannot at the same time be happy and unhappy.”160 

Many other refutations of Skepticism occur in Augustine’s later works, notably On the Free 

Choice of the Will (389–395), On the Trinity (399/400–416/421), and The City of God (413–

426/427). In the last, Augustine proposes other examples of things about which people can be 

absolutely certain. Again in explicit refutation of the Skeptics of the Academy, he argues that if a 

person is deceived, then it is certain that he exists. Expressing the point in the first person, 

as René Descartes (1596–1650) did some 1,200 years later, Augustine says, “If I am deceived, 

then I exist” (Si fallor, sum).161 A variation on that line of reasoning appears in On the Trinity, in 

which he argues that if he is deceived, he is at least certain that he is alive. 

Augustine also points out that since he knows, he knows that he knows, and he notes that this can 

be reiterated an infinite number of times: if I know that I know that I am alive, then I know that I 

know that I know that I am alive. In 20th-century epistemic logic, that thesis was codified as the 

                                                             
158 https://www.britannica.com/topic/biography/saint-augustine/ 
159 Ibid. 
160 Augustine, Against the Academicians, Denis J. Kavanachi (tran.), (New York: Image Books, 1943), bk.1, c.20, 
no.43. 
161 St. Augustine, D Civitat Dei, bk.xi. 

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axiom “If A knows that p, then A knows that A knows that p.” In The City of God, Augustine 

claims that he knows that he loves: “For neither am I deceived in this, that I love, since in those 

things which I love I am not deceived.”162 With Skepticism thus refuted, Augustine simply 

denies that he has ever been able to doubt what he has learned through his sensations or even 

through the testimony of most people. 

One thousand years passed before Skepticism recovered from Augustine’s criticisms, but then it 

arose like the phoenix of Egyptian mythology. Meanwhile, Augustine’s Platonic epistemology 

dominated the Middle Ages until the mid-13th century, when St. Albertus Magnus (1200–80) 

and his student St. Thomas Aquinas (1224/25–1274) developed an alternative to Augustinian 

illuminationism. 

 

10.2 Medieval philosophy 

 

10.2.1 St. Anselm of Canterbury 

The phrase that St. Anselm of Canterbury (c. 1033–1109) used to describe his philosophy—

namely, “faith seeking reason” (fides quaerens intellectum)—well 

characterizes medieval philosophy as a whole. All the great medieval philosophers—Christian, 

Jewish, and Islamic alike—were also theologians. Virtually every object of interest was related 

to their belief in God, and virtually every solution to every problem, including the problem of 

knowledge, contained God as an essential part. Indeed, Anselm himself equated truth and 

intelligibility with God. As he noted at the beginning of his Proslogion (1077–78), however, 

there is a tension between the view that God is truth and intelligibility and the fact that humans 

have no perception of God. How can there be knowledge of God, he asks, when all knowledge 

comes through the senses and God, being immaterial, cannot be sensed? His answer is to 

distinguish between knowing something by being acquainted with it through sensation and 

knowing something through a description. Knowledge by description is possible using concepts 

formed on the basis of sensation. Thus, all knowledge of God depends upon the description that 

he is “the thing than which a greater cannot be conceived.”163 From that premise Anselm infers, 

in his ontological argument for the existence of God, that humans can know that there exists a 

God that is all-powerful, all-knowing, all-just, all-merciful, and immaterial. Eight hundred years 

later the British philosopher Bertrand Russell would develop an epistemological theory based on 

a similar distinction between knowledge by acquaintance and knowledge by description,164 

though he would have vigorously denied that the distinction could be used to show that God 

exists. 

 

                                                             
162 Ibid., bk.xiii. 
163 Ibid. 
164 https://www.britannica.com/biography/betrand-russell/ 

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10.2.2 St. Thomas Aquinas 

 

With the translation into Latin of Aristotle’s On the Soul in the early 13th century, 

the Platonic and Augustinian epistemology that dominated the early Middle Ages was gradually 

displaced. Following Aristotle, Aquinas recognized different kinds of knowledge. Sensory 

knowledge arises from sensing particular things. Because it has individual things as its object 

and is shared with brute animals, however, sensory knowledge is a lower form of awareness than 

scientific knowledge, which is characterized by generality.165 To say that scientific knowledge is 

characteristically general is not to diminish the importance of specificity: scientific knowledge 

also should be rich in detail, and God’s knowledge is the most detailed of all. The detail, 

however, must be essential to the kind of thing being studied and not peculiar to certain instances 

of it. Aquinas thought that, though the highest knowledge humans can possess is knowledge of 

God, knowledge of physical objects is better suited to human capabilities.166 Only that kind of 

knowledge will be considered here. 

 

Aquinas’s discussion of knowledge in the Summa theologiae is an elaboration on the thought of 

Aristotle. Aquinas claims that knowledge is obtained when the active intellect abstracts a concept 

from an image received from the senses. In one account of that process, abstraction is the act of 

isolating from an image of a particular object the elements that are essential to its being an object 

of that kind. From the image of a dog, for example, the intellect abstracts the ideas of being alive, 

being capable of reproduction and movement, and whatever else might be essential to being a 

dog. Those ideas are distinguished from ideas of properties that are peculiar to particular dogs, 

such as the property of being owned by Smith or the property of weighing 20 pounds. 

 

As stated earlier, Aristotle typically spoke of the form of an object as being in the mind or 

intellect of the knower and the matter as being outside it. Although it was necessary for Aristotle 

to say something like that in order to escape the absurdity of holding that material objects exist in 

the mind exactly as they do in the physical world, there is something unsatisfying about it. 

Physical things contain matter as an essential element, and, if their matter is no part of what is 

known, then it seems that human knowledge is incomplete. In order to counter that worry, 

Aquinas revised Aristotle’s theory to say that not only the form but also the “species” of an 

object is in the intellect.167 A species is a combination of form and something like a 

general idea of matter, which Aquinas called “common matter.” Common matter is contrasted 

with “individuated matter,” which is the stuff that constitutes the physical bulk of an object. 

 

                                                             
165 https://www.britannica.com/biography/saint-thomas-aquinas/ 
166 Ibid. 
167 Ibid. 

https://www.britannica.com/biography/Saint-Thomas-Aquinas
https://www.britannica.com/topic/Latin-language
https://www.merriam-webster.com/dictionary/Platonic
https://www.britannica.com/biography/Aristotle
https://www.britannica.com/topic/Summa-theologiae
https://www.britannica.com/topic/active-intellect
https://www.britannica.com/science/senses
https://www.britannica.com/topic/mind
https://www.britannica.com/topic/idea
https://www.merriam-webster.com/dictionary/constitutes


82 
 

One objection to the theory is that it seems to follow from it that the objects of human knowledge 

are ideas rather than things. That is, if knowing a thing consists of having its form and species in 

one’s intellect, then it appears that the form and species, not the thing, is what is known. It might 

seem, then, that Aquinas’s view is a type of idealism. 

 

Aquinas anticipated that kind of criticism in a number of ways. Because it includes the idea of 

matter, the species of an object seems more like the object itself than does an immaterial 

Aristotelian form. Moreover, for Aquinas science does not aim at knowing any particular object 

but rather at knowing what is common to all objects of a certain kind.168 In that respect, 

Aquinas’s views are similar to those of modern scientists. For example, the particular billiard 

ball that Smith drops from his window is of no direct concern to physics. What physicists are 

interested in are the laws that govern the behaviour of any falling object. 

As assuaging as such considerations might be, they do not blunt the main force of the objection. 

In order to meet it, Aquinas introduced a distinction between what is known and that by which 

what is known is known. To specify what is known—say, an individual dog—is to specify the 

object of knowledge. To specify that by which what is known is known—say, the image or the 

species of a dog—is to specify the apparatus of knowledge. Thus, the species of a thing that is 

known is not itself an object of knowledge, though it can become an object of knowledge by 

being reflected upon. 

 

 

 

10.2.3 John Duns Scotus 

 

Although he accepted some aspects of Aristotelian abstractionism, John Duns Scotus (c. 1266–

1308) did not base his account of human knowledge on that alone. According to him, there are 

four classes of things that can be known with certainty.169 First, there are things that are 

knowable simpliciter, including true identity statements such as “Cicero is Tully” and 

propositions, later called analytic, such as “Man is rational.” Duns Scotus claimed that such 

truths “coincide” with that which makes them true. One consequence of his view is that the 

negation of a simple truth is always inconsistent, even if it is not explicitly contradictory. The 

negation of “The whole is greater than any proper part,” for example, is not explicitly 

contradictory, as is “Snow is white and snow is not white.” Nevertheless, it is inconsistent, 

because there is no possible situation in which it is true.  

 

The second class consists of things that are known through experience, where “experience” is 

understood in an Aristotelian sense that implies numerous encounters. The knowledge afforded 

by experience is inductive, grounded in the principle that “whatever occurs in a great many 

                                                             
168 Ibid. 
169 https://www.britannica.com/biography/blessed-john-duns-scotus/ 

https://www.britannica.com/topic/idealism
https://www.merriam-webster.com/dictionary/criticism
https://www.britannica.com/science/physics-science
https://www.merriam-webster.com/dictionary/assuaging
https://www.britannica.com/biography/Blessed-John-Duns-Scotus
https://www.britannica.com/biography/Blessed-John-Duns-Scotus
https://www.britannica.com/topic/certainty-philosophy
https://www.britannica.com/topic/analytic-proposition
https://www.britannica.com/topic/truth-philosophy-and-logic


83 
 

instances by a cause that is not free is the natural effect of that cause.” It is important to note that 

Duns Scotus’s confidence in induction did not survive the Middle Ages. Nicholas of 

Autrecourt (1300–50), whose views anticipated the radical skepticism of the Scottish 

Enlightenment philosopher David Hume, argued at length that no amount of observed correlation 

between two types of events is sufficient to establish a necessary causal connection between 

them and, thus, that inferences based on causal assumptions are never rationally justified. 

 

The third class consists of things that directly concern one’s own actions. Humans who are 

awake, for example, know immediately and with certainty—and not through any inference—that 

they are awake. Similarly, they know with certainty that they think and that they see and hear 

and have other sense experiences. Even if a sense experience is caused by a defective sense 

organ, it remains true that one is directly aware of the content of the sensation. When one has the 

sensation of seeing a round object, for example, one is directly aware of the roundness even if 

the thing one is seeing is not really round. 

Finally, the fourth class contains things that are knowable through the human senses. Apparently 

unconcerned by the threat of skepticism, Duns Scotus maintained that sensation affords 

knowledge of the heavens, the earth, the sea, and all the things that are in them. 

Duns Scotus’s most important contribution to epistemology is his distinction between “intuitive” 

and “abstractive” cognition.170 Intuitive cognition is the immediate and indubitable awareness of 

the existence of a thing. It is knowledge “precisely of a present object [known] as being present 

and of an existent object [known] as being existent.” If a person sees Socrates before him, then, 

according to Duns Scotus, he has intuitive knowledge of the proposition that Socrates exists and 

of the proposition that Socrates is the cause of that knowledge. Abstractive cognition, in contrast, 

is knowledge about a thing that is abstracted from, or logically independent of, that thing’s actual 

existence or nonexistence. 

 

10.2.4 William of Ockham 

 

Several parts of Duns Scotus’s account are vulnerable to skeptical challenges, for instance, his 

endorsement of the certainty of knowledge based on sensation and his claim that intuitive 

knowledge of an object guarantees its existence. William of Ockham (c. 1285–1349?) radically 

revised Duns Scotus’s theory of intuitive knowledge. Unlike Duns Scotus, Ockham did not 

require the object of intuitive knowledge to exist; nor did he hold that intuitive knowledge must 

be caused by its object. To the question “What is the distinction between intuitive and abstractive 

knowledge?,” Ockham answered that they are simply different.171 His answer notwithstanding, it 

is characteristic of intuitive knowledge, according to Ockham, that it is unmediated. There is no 

gap between the knower and the known that might undermine certainty: “I say that the thing 

                                                             
170 Ibid.  
171A.H. Armsstrong. An Introduction to Ancient Philosophy (Methuen: London University, 1965), 33. 

https://www.britannica.com/topic/induction-reason
https://www.britannica.com/biography/Nicholas-of-Autrecourt
https://www.britannica.com/biography/Nicholas-of-Autrecourt
https://www.britannica.com/topic/skepticism
https://www.britannica.com/event/Scottish-Enlightenment
https://www.britannica.com/event/Scottish-Enlightenment
https://www.britannica.com/biography/David-Hume
https://www.merriam-webster.com/dictionary/inferences
https://www.merriam-webster.com/dictionary/skepticism
https://www.britannica.com/topic/intuition
https://www.merriam-webster.com/dictionary/indubitable
https://www.britannica.com/biography/Socrates
https://www.britannica.com/biography/William-of-Ockham
https://www.merriam-webster.com/dictionary/vulnerable
https://www.britannica.com/biography/William-of-Ockham


84 
 

itself is known immediately without any medium between itself and the act by which it is seen or 

apprehended.”172 

 

According to Ockham, there are two kinds of intuitive knowledge: natural and supernatural.173 In 

cases of natural intuitive knowledge, the object exists, the knower judges that the object exists, 

and the object causes the knowledge. In cases of supernatural intuitive knowledge, the object 

does not exist, the knower judges that the object does not exist, and God is the cause of the 

knowledge. 

Ockham recognized that God might cause one to think that one has intuitive knowledge of an 

existent object when in fact there is no such object, but this would be a case of false belief, he 

contends, not intuitive knowledge. Unfortunately, by acknowledging that there is no way to 

distinguish between genuine intuitive knowledge and divine counterfeits, Ockham effectively 

conceded the issue to the skeptics.174 

Later medieval philosophy followed a fairly straight path toward skepticism. John of 

Mirecourt (flourished 14th century) was censured by the University of Paris in 1347 for 

maintaining, among other things, that external reality cannot be known with certainty because 

God can cause illusions to seem real.175 A year earlier Nicholas of Autrecourt was condemned by 

Pope Clement VI for holding that one can have certain knowledge only of the logical principles 

of identity and contradiction and the immediate reports of sensation.176 As noted above, he 

denied that causal relations exist; he also denied the reality of substance. He credited those 

errors, along with many others, to Aristotle, about whom he said, “In all his natural philosophy 

and metaphysics, Aristotle had hardly reached two evidently certain conclusions, perhaps not 

even a single one.”177 By that time the link between skepticism and criticism of Aristotle had 

become fairly strong. In On My Ignorance and That of Many Others (1367), for example, the 

Italian poet Petrarch (1304–74) cited Aristotle as “the most famous” of those who do not have 

knowledge.178 

 

 

 

 

 

 

 

                                                             
172 Ibid. 
173 Ibid, 34. 
174 Ibid.51-56. 
175 https://www.britannica.com/biography/john-of-mirecourt/ 
176A.H. Armsstrong. An Introduction to Ancient Philosophy, op.cit. 
177 Ibid. 
178 https://www.britannica.com/biography/petrarch/ 

https://www.britannica.com/topic/belief
https://www.merriam-webster.com/dictionary/medieval
https://www.britannica.com/topic/philosophy
https://www.britannica.com/biography/John-of-Mirecourt
https://www.britannica.com/biography/John-of-Mirecourt
https://www.merriam-webster.com/dictionary/censured
https://www.britannica.com/topic/Universities-of-Paris-I-XIII
https://www.merriam-webster.com/dictionary/illusions
https://www.britannica.com/biography/Clement-VI
https://www.britannica.com/topic/metaphysics
https://www.britannica.com/biography/Petrarch


85 
 

CHAPTER ELEVEN 

THE HISTORY OF EPISTEMOLOGY: MODERN PHILOSOPHY 

 

11.1 The Rise of Modern Epistemology 

 

For most of the middle Ages there was no distinction between theology and science (scientia). 

Science was knowledge that was deduced from self-evident principles, and theology was 

knowledge that received its principles from God, the source of all principles. By the 14th 

century, however, scientific and theological thinking began to diverge. Roughly speaking, 

theologians began to argue that human knowledge was narrowly circumscribed. The 

omnipotence of God was often invoked in order to undercut the pretensions of human reason, 

and in place of rationalism in theology they promoted a kind of fideism (i.e., a philosophy based 

entirely on faith).179 

 

The Italian theologian Gregory of Rimini (died 1358) exemplified the development. Inspired by 

Ockham, Gregory argued that, whereas science concerns what is accessible to humans through 

natural means, that is, through sensation and intelligence, theology deals with what is accessible 

only in a supernatural way.180 Thus, theology is not scientific. The role of theology is to explain 

the meaning of the Bible and the articles of faith and to deduce conclusions from them. Since the 

credibility of the Bible rests upon belief in divine revelation, theology lacks a rational 

foundation. Furthermore, since there is neither self-evident knowledge of God nor any natural 

experience of him, humans can have only an abstract understanding of what he is. 

 

Ockham and Gregory did not intend their views to undermine theology. To the contrary, for 

them theology is in a sense more certain than science, because it is built upon principles that are 

guaranteed to be true by God, whereas the principles of science must be as fallible as their 

human creators. Unfortunately for theology, however, the prestige of science increased in the 

16th century and skyrocketed in the 17th and 18th centuries. Modern thinkers preferred to reach 

their own conclusions by using reason and experience even if ultimately those conclusions did 

not have the authority of God to support them. As theologians lost confidence in reason, other 

thinkers, who had little or no commitment to Aristotelian thought, became its champions, thus 

furthering the development of modern science. 

 

11.2 Faith and reason 

 

Although modern philosophers as a group are usually thought to be purely secular thinkers, in 

fact nothing could be further from the truth. From the early 17th century until the middle of the 

18th century, all the great philosophers incorporated substantial religious elements into their 

                                                             
179 https://www.britannica.com/topic/philosophy/ 
180 https://www.britannica.com/biography/gregory-of-rimini/ 

https://www.britannica.com/topic/rationalism
https://www.britannica.com/topic/fideism
https://www.britannica.com/topic/philosophy
https://www.britannica.com/biography/Gregory-of-Rimini
https://www.britannica.com/topic/Bible
https://www.britannica.com/topic/revelation
https://www.merriam-webster.com/dictionary/prestige
https://www.merriam-webster.com/dictionary/secular
https://www.britannica.com/topic/truth-philosophy-and-logic


86 
 

work. In his Meditations (1641), for example, René Descartes offered two distinct proofs of 

the existence of God and asserted that no one who does not have a rationally well-founded belief 

in God can have knowledge in the proper sense of the term.181 Benedict de Spinoza (1632–77) 

began his Ethics (1677) with a proof of God’s existence and then discussed at length 

its implications for understanding all reality. And George Berkeley (1685–1753) explained the 

apparent stability of the sensible world by appealing to God’s constant thought of it. 

 

Among the reasons modern philosophers are mistakenly thought to be primarily secular thinkers 

is that many of their epistemological principles, including some that were designed to defend 

religion, were later interpreted as subverting the rationality of religious belief. The views 

of Thomas Hobbes (1588–1679) might briefly be considered in that connection. In contrast to the 

standard view of the Middle Ages that propositions of faith are rational, Hobbes argued that such 

propositions belong not to the intellect but to the will. The significance of religious propositions, 

in other words, lies not in what they say but in how they are used. To profess a religious 

proposition is not to assert a factual claim about the world, which may then be supported or 

refuted with reasons, but merely to give praise and honour to God and to obey the commands of 

lawful religious authorities. Indeed, one does not even need to understand the meanings of the 

words in the proposition in order for this function to be fulfilled; simply mouthing them would 

be sufficient.182 

 

In An Essay Concerning Human Understanding (1690), John Locke further eroded 

the intellectual status of religious propositions by making them subordinate to reason in several 

respects.183 First, reason can restrict the possible content of propositions allegedly revealed by 

God; in particular, no proposition of faith can be a contradiction. Furthermore, because 

no revelation can contain an idea not derived from sense experience, one should not believe St. 

Paul when he speaks of experiencing things as “eye has not seen, nor ear heard, nor has it entered 

into the heart of man to conceive.” Another respect in which reason takes precedence over faith 

is that knowledge based on immediate sense experience (what Locke called “intuitive 

knowledge”) is always more certain than any alleged revelation. Thus, people who see that 

someone is dead cannot have it revealed to them that that person is at that moment alive. 

Rational proofs in mathematics and science also cannot be controverted by divine revelation. The 

interior angles of a rectangle equal 360°, and no alleged revelation to the contrary is credible. In 

short, wrote Locke, “Nothing that is contrary to, and inconsistent with, the clear and self-evident 

dictates of reason, has a right to be urged or assented to as a matter of faith.”184 

 

                                                             
181A.H. Armsstrong. An Introduction to Ancient Philosophy, op.cit. 
182 Ibid. 
183 Ibid. 
184 Ibid. 

https://www.britannica.com/topic/Meditations-on-First-Philosophy-in-Which-Is-Proved-the-Existence-of-God-and-the-Immortality-of-the-Soul
https://www.britannica.com/biography/Rene-Descartes
https://www.britannica.com/topic/existence-of-God
https://www.britannica.com/biography/Benedict-de-Spinoza
https://www.britannica.com/topic/evidence-law
https://www.merriam-webster.com/dictionary/implications
https://www.britannica.com/biography/George-Berkeley
https://www.britannica.com/topic/religious-belief
https://www.britannica.com/biography/Thomas-Hobbes
https://www.britannica.com/event/Middle-Ages
https://www.britannica.com/topic/Essay-Concerning-Human-Understanding
https://www.britannica.com/biography/John-Locke
https://www.merriam-webster.com/dictionary/intellectual
https://www.britannica.com/topic/revelation
https://www.britannica.com/topic/idea
https://www.britannica.com/biography/Saint-Paul-the-Apostle
https://www.britannica.com/biography/Saint-Paul-the-Apostle
https://www.merriam-webster.com/dictionary/precedence
https://www.merriam-webster.com/dictionary/alleged
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87 
 

What space, then, does faith occupy in the mansion of human beliefs? According to Locke, it 

shares a room with probable truths, which are propositions of which reason cannot be certain.185 

There are two types of probable truth: that which concerns observable matters of fact and that 

which goes “beyond the discovery of our sense.”186 Religious propositions can belong to either 

category, as can empirical and scientific propositions. Thus, the propositions “Caesar crossed the 

Rubicon” and “Jesus walked on water” belong to the first category, because they make claims 

about events that would be observable if they occurred. On the other hand, propositions like 

“Heat is caused by the friction of imperceptibly small bodies” and “Angels exist” belong to the 

second category, because they concern entities that by definition cannot be objects of sense 

experience. 

 

Although it might seem that Locke’s mixing of religious and scientific claims helped to secure a 

place for the former, in fact it did not, for Locke also held that “reason must judge” whether or 

not something is a revelation and, more generally, that “reason must be our last judge and guide 

in everything.”187 Although that maxim was intended to reconcile reason and revelation—indeed, 

Locke called reason “natural revelation” and revelation “natural reason enlarged by a new set of 

discoveries communicated by God”188—over the course of the subsequent 200 years, reason 

repeatedly judged that alleged revelations had no scientific or intellectual standing. 

 

Despite the strong religious elements in the thought of modern philosophers, especially those 

writing before the middle of the 18th century, the vast majority of contemporary epistemologists 

have been interested only in the purely secular aspects of their work. Accordingly, those aspects 

will predominate in the following discussion. 

 

11.3 Epistemology and modern science 

 

The Polish astronomer Nicolaus Copernicus (1473–1543) argued in On the Revolutions of the 

Celestial Spheres (1543) that Earth revolves around the Sun.189 His theory was epistemologically 

shocking for at least two reasons. First, it directly contravened the way in which humans 

experienced their relation to the Sun, and in doing so it made ordinary nonscientific reasoning 

about the world seem unreliable—indeed, like a kind of superstition. Second, it contradicted the 

account presented in several books of the Bible, most importantly the story in Genesis of the 

structure of the cosmos, according to which Earth is at the centre of 

                                                             
185 Ibid. 
186 Ibid. 
187https://www.britannica.com/biography/john-locke/ 
188 Ibid. 
189 Nicolaus Copernicus, On the Revolution of the Celestial Spheres (1943), 
https://www.environmentandsociety.org. 

https://www.britannica.com/science/probability
https://www.merriam-webster.com/dictionary/empirical
https://www.merriam-webster.com/dictionary/reconcile
https://www.britannica.com/biography/Nicolaus-Copernicus
https://www.britannica.com/science/Copernican-system
https://www.britannica.com/place/Sun
https://www.britannica.com/topic/Genesis-British-rock-group
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88 
 

creation.190If Copernicus were right, then the Bible could no longer be treated as a reliable source 

of scientific knowledge. 

Many of the discoveries of the Italian astronomer Galileo Galilei (1564–1642) were equally 

unsettling.191 His telescope seemed to reveal that unaided human vision gives false, or at least 

seriously incomplete, information about the nature of celestial bodies. In addition, his 

mathematical descriptions of physical phenomena indicated that much of sense experience of 

these phenomena contributes nothing to knowledge of them. 

Another counterintuitive theory of Galileo was his distinction between the “primary” and the 

“secondary” qualities of an object. Whereas primary qualities—such as figure, quantity, 

and motion—are genuine properties of things and are knowable by mathematics, secondary 

qualities—such as colour, odour, taste, and sound—exist only in human consciousness and are 

not part of the objects to which they are normally attributed.192 

 

11.4 René Descartes 

 

Both the rise of modern science and the rediscovery of skepticism were important influences on 

René Descartes. Although he believed that certain knowledge was possible and that modern 

science would one day enable humans to become the masters of nature, he also thought 

that skepticism presented a legitimate challenge that needed an answer, one that only he could 

provide. 

 

The challenge of skepticism, as Descartes saw it, is vividly described in his Meditations (1641). 

He considered the possibility that an “evil genius” with extraordinary powers has deceived him 

to such an extent that all his beliefs are false. But it is not possible, Descartes contended, that all 

his beliefs are false, for if he has false beliefs, he is thinking, and if he is thinking, then he exists. 

Therefore, his belief that he exists cannot be false, as long as he is thinking. This line of 

argument is summarized in the formula cogito, ergo sum (“I think, therefore I am”).193 

 

Descartes distinguished two sources of knowledge: intuition and deduction.194 Intuition is an 

unmediated mental “seeing,” or direct apprehension. Descartes’s intuition of his own thinking 

guarantees that his belief that he is thinking is true. Although his formula might suggest that his 

belief that he exists is guaranteed by deduction rather than intuition (because it contains the 

term therefore), in the Objections and Replies (1642) he stated explicitly that the certainty of this 

belief also is based upon intuition. 

                                                             
190B.P. Beckwith,Religion, Philosophy and Science: An Introduction to Logical Positivism (New York: Philosophical 
library, 1957). 
191https://www.britannica.com/biography/john-locke/galileo-galilei/ 
192 Ibid. 
193https://www.britannica.com/biography/ree-descartes/ 
194 Ibid. 

https://www.britannica.com/place/Copernicus-lunar-crater
https://www.britannica.com/topic/Bible
https://www.britannica.com/biography/Galileo-Galilei
https://www.britannica.com/science/optical-telescope
https://www.merriam-webster.com/dictionary/counterintuitive
https://www.britannica.com/topic/primary-quality
https://www.britannica.com/science/motion-mechanics
https://www.britannica.com/topic/secondary-quality
https://www.britannica.com/topic/secondary-quality
https://www.britannica.com/science/color
https://www.britannica.com/science/odor
https://www.britannica.com/science/taste-sense
https://www.britannica.com/science/sound-physics
https://www.britannica.com/topic/consciousness
https://www.britannica.com/biography/Rene-Descartes
https://www.britannica.com/topic/skepticism
https://www.merriam-webster.com/dictionary/skepticism
https://www.merriam-webster.com/dictionary/legitimate
https://www.britannica.com/topic/Meditations-on-First-Philosophy-in-Which-Is-Proved-the-Existence-of-God-and-the-Immortality-of-the-Soul
https://www.britannica.com/topic/cogito-ergo-sum
https://www.merriam-webster.com/dictionary/intuition
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89 
 

 

If one could know only that one thinks and that one exists, human knowledge would be 

depressingly meager. Accordingly, Descartes attempted to broaden the limits of knowledge by 

proving to his own satisfaction that God exists, that the standard for knowing something is 

having a “clear and distinct” idea of it. That mind is more easily known than body, that the 

essence of matter is extension, and, finally, that most of his former beliefs are true. 

 

Unfortunately for Descartes, few people were convinced by these arguments. One major problem 

with them has come to be known as the “Cartesian circle.”195 Descartes’s argument to show that 

his knowledge extends beyond his own existence depends upon the claim that whatever he 

perceives “clearly and distinctly” is true. That claim in turn is supported by his proof of the 

existence of God, together with the assertion that God, because he is not a deceiver, would not 

cause Descartes to be deceived in what he clearly and distinctly perceives. But because 

the criterion of clear and distinct perception presupposes the existence of God, Descartes cannot 

rely upon it in order to guarantee that he has not been deceived (i.e., that he did not make a 

mistake) in the course of proving that God exists. Therefore, he does not know that his proof 

is cogent. But if he does not know that, then he cannot use the criterion of clear and distinct 

perception to show that he knows more than that he exists. 

 

11.5 John Locke 

 

Whereas rationalist philosophers such as Descartes held that the ultimate source of human 

knowledge is reason, empiricists such as John Locke argued that the source is experience 

(see Rationalism and empiricism).196 Rationalist accounts of knowledge also typically involved 

the claim that at least some kinds of ideas are “innate,” or present in the mind at (or even before) 

birth. For philosophers such as Descartes and Gottfried Wilhelm Leibniz (1646–1716), 

the hypothesis of innateness is required in order to explain how humans come to have ideas of 

certain kinds.197 Such ideas include not only mathematical concepts such as numbers, which 

appear not to be derived from sense experience, but also, according to some thinkers, certain 

general metaphysical principles, such as “every event has a cause.”  

Locke claimed that that line of argument has no force. He held that all ideas (except those that 

are “trifling”) can be explained in terms of experience.198 Instead of attacking the doctrine 

of innate ideas directly, however, his strategy was to refute it by showing that it is explanatorily 

otiose and hence dispensable. 

                                                             
195https://www.britannica.com/topic/cartesian-circle/ 
196https://www.britannica.com/topic/epistemology/ 
197 H.C. Ezebuilo, Descartes, Leibniz and Spinoza: A Brief Survey of Rationalism, AMAMIHE: Journal of Applied 
Philosophy, 18(6), (2020, 106-110. 
198 H.C. Ezebuilo, Locke, Berkeley and Hume: A Brief Survey of Empiricism, International Journal of Research in 
Education, Humanities and Commerce, 1(2), (2020), 88. 

https://www.britannica.com/topic/mind
https://www.britannica.com/science/matter
https://www.britannica.com/topic/Cartesian-circle
https://www.merriam-webster.com/dictionary/criterion
https://www.merriam-webster.com/dictionary/cogent
https://www.britannica.com/biography/John-Locke
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There are two kinds of experience, according to Locke: observation of external objects—

i.e., sensation—and observation of the internal operations of the mind.199 Locke called the latter 

kind of experience, for which there is no natural word in English, “reflection.” Some examples of 

reflection are perceiving, thinking, doubting, believing, reasoning, knowing, and willing. 

As Locke used the term, a “simple idea” is anything that is an “immediate object of perception” 

(i.e., an object as it is perceived by the mind) or anything that the mind “perceives in itself” 

through reflection.200 Simple ideas, whether they are ideas of perception or ideas of reflection, 

may be combined or repeated to produce “compound ideas,” as when the compound idea of an 

apple is produced by bringing together simple ideas of a certain colour, texture, odour, and 

figure. Abstract ideas are created when “ideas taken from particular beings become general 

representatives of all of the same kind.” 

The “qualities” of an object are its powers to cause ideas in the mind. One consequence of that 

usage is that, in Locke’s epistemology, words designating the sensible properties of objects are 

systematically ambiguous. The word red, for example, can mean either the idea of red in the 

mind or the quality in an object that causes that idea. Locke distinguished between primary and 

secondary qualities, as Galileo did. According to Locke, primary qualities, but not secondary 

qualities, are represented in the mind as they exist in the object itself.201 The primary qualities of 

an object, in other words, resemble the ideas they cause in the mind. Examples of primary 

qualities include “solidity, extension, figure, motion, or rest, and number.” Secondary qualities 

are configurations or arrangements of primary qualities that cause sensible ideas such as sounds, 

colours, odours, and tastes.202 Thus, according to Locke’s view, the phenomenal redness of a fire 

engine is not in the fire engine itself, but its phenomenal solidity is. Similarly, the phenomenal 

sweet odour of a rose is not in the rose itself, but its phenomenal extension is. 

In Book IV of An Essay Concerning Human Understanding (1689), Locke defined knowledge as 

“the perception of the connexion of and agreement, or disagreement and repugnancy of any of 

our ideas.”203 Knowledge so defined admits of three degrees, according to Locke.204 The first is 

what he called “intuitive knowledge,” in which the mind “perceives the agreement or 

disagreement of two ideas immediately by themselves, without the intervention of any other.” 

Although Locke’s first examples of intuitive knowledge are analytic propositions such as 

“white is not black,” “a circle is not a triangle,” and “three are more than two,” later he said that 

“the knowledge of our own being we have by intuition.” Relying on the metaphor of light as 

Augustine and others had, Locke said of this knowledge that “the mind is presently filled with 

                                                             
199https://www.britannica.com/biography/john-locke/ 
200 H.C. Ezebuilo, Locke, Berkeley and Hume, 87-91. 
201 Ibid. 
202 Ibid. 
203https://www.britannica.com/topic/essay-concerning-human-understanding/ 
204 Ibid. 

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91 
 

the clear light of it. It is on this intuition that depends all the certainty and evidence of all our 

knowledge.” 

The second degree of knowledge obtains when “the mind perceives the agreement or 

disagreement of…ideas, but not immediately.” In these cases, some mediating idea makes it 

possible to see the connection between two other ideas. In a demonstration (or proof), for 

example, the connection between any premise and the conclusion is mediated by 

other premises and by the laws of logic. Demonstrative knowledge, although certain, is not as 

certain as intuitive knowledge, according to Locke, because it requires effort and attention to go 

through the steps needed to recognize the certainty of the conclusion. 

A third degree of knowledge, “sensitive knowledge,” is roughly the same as what Duns Scotus 

called “intuitive cognition”—namely, the perception of “the particular existence of finite beings 

without us.” Unlike intuitive cognition, however, Locke’s sensitive knowledge is not the most 

certain kind of knowledge it is possible to have. For him, it is less certain than intuitive or 

demonstrative knowledge. 

Next in certainty to knowledge is probability,205 which Locke defined as the appearance of 

agreement or disagreement of ideas with each other. Like knowledge, probability admits of 

degrees, the highest of which attaches to propositions endorsed by the general consent of all 

people in all ages. Locke may have had in mind the virtually general consent of his 

contemporaries in the proposition that God exists, but he also explicitly mentioned beliefs 

about causal relations. 

The next highest degree of probability belongs to propositions that hold not universally but for 

the most part, such as “people prefer their own private advantage to the public good.”206 This 

sort of proposition is typically derived from history. A still lower degree of probability attaches 

to claims about specific facts—for example, that a man named Julius Caesar lived a long time 

ago. Problems arise when testimonies conflict, as they often do, but there is no simple rule or set 

of rules that determines how one ought to resolve such controversies. 

Probability can concern not only objects of possible sense experience, as most of the foregoing 

examples do, but also things that are outside the sensible realm, such as angels, 

devils, magnetism, and molecules. 

 

11.6 George Berkeley 

 

The next great figure in the development of empiricist epistemology was George 

Berkeley (1685–1753). In his major work, A Treatise Concerning the Principles of Human 

                                                             
205 Ibid. 
206 Ibid. 

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Knowledge (1710), Berkeley asserted that nothing exists except ideas and spirits (minds 

or souls).207 He distinguished three kinds of ideas: those that come from sense experience which 

corresponds to Locke’s simple ideas of perception; those that come from “attending to the 

passions and operations of the mind”  which corresponds to Locke’s ideas of reflection; and 

those that come from compounding, dividing, or otherwise representing ideas which corresponds 

to Locke’s compound ideas. By spirit Berkeley meant “one simple, undivided, active being.” 

The activity of spirits consists of both understanding and willing: understanding is spirit 

perceiving ideas, and will is spirit producing ideas.  

 

For Berkeley, ostensibly physical objects like tables and chairs are really nothing more than 

collections of sensible ideas.208 Since no idea can exist outside a mind, it follows that tables and 

chairs, as well all the other furniture of the physical world, exist only insofar as they are in the 

mind of someone—i.e., only insofar as they are perceived. For any non-thinking being, esse est 

percipi (“to be is to be perceived”). The clichéd question of whether a tree falling in an 

uninhabited forest makes a sound was inspired by Berkeley’s philosophy, though he never 

considered it in those terms. He did, however, consider the implicit objection and gave various 

answers to it. He sometimes said that a table in an unperceived room would be perceived if 

someone were there. That conditional response, however, is inadequate. Granted that the table 

would exist if it were perceived, does it exist when it is not perceived? Berkeley’s more pertinent 

answer was that even when no human is perceiving a table or other such object, God is, and it is 

God’s thinking that keeps the otherwise unperceived object in existence.209 

 

Although that doctrine initially strikes most people as strange, Berkeley claimed that he was 

merely describing the commonsense view of reality. To say that colours, sounds, trees, dogs, and 

tables are ideas is not to say that they do not really exist. It is merely to say what they really are. 

Moreover, to say that animals and pieces of furniture are ideas is not to say that they are 

diaphanous, gossamer, and evanescent. Opacity, density, and permanence are also ideas that 

partially constitute those objects. 

 

Berkeley supported his main thesis with a syllogistic argument: physical things—such as trees, 

dogs, and houses—are things perceived by sense; things perceived by sense are ideas; therefore, 

physical things are ideas.210 If one objects that the second premise of the syllogism is false—

people sense things, not ideas—Berkeley would reply that there are no sensations without ideas 

and that it makes no sense to speak of some additional thing that ideas are supposed to represent 

or resemble. Unlike Locke, Berkeley did not believe that there is anything “behind” or 

                                                             
207https://www.britannica.com/biography/george-berkeley/ 
208 H.C. Ezebuilo, Locke, Berkeley and Hume, 92. 
209 Ibid. 
210 Ibid.,94-95. 

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“underlying” ideas in a world external to the mind. Indeed, Berkeley claimed that no clear idea 

can be attached to that notion. 

 

One consequence of Berkeley’s view is that Locke’s distinction between primary and secondary 

qualities is spurious. Extension, figure, motion, rest, and solidity are as much ideas as green, 

loud, and bitter are; there is nothing special about the former kind of idea. Furthermore, matter, 

as philosophers conceive it, does not exist. Indeed, it is contradictory, for matter is supposedly 

unsensed extension, figure, and motion, but since extension, figure, and motion are ideas, they 

must be sensed. 

 

Berkeley’s doctrine that things unperceived by human beings continue to exist in the thought of 

God was not novel. It was part of the traditional belief of Christian philosophers from Augustine 

through Aquinas and at least to Descartes that God not only creates all things but also keeps 

them in existence by thinking of them. According to that view, if God were ever to stop thinking 

of a creature, it would immediately be annihilated. 

 

11.7 David Hume 

 

Although Berkeley rejected the Lockean notions of primary and secondary qualities and matter, 

he retained Locke’s belief in the existence of mind, substance, and causation as an unseen force 

or power in objects. David Hume, in contrast, rejected all these notions. 

 

11.7.1 Kinds of Perception 

 

Hume recognized two kinds of perception: “impressions” and “ideas.”211 Impressions are 

perceptions that the mind experiences with the “most force and violence,” and ideas are the 

“faint images” of impressions. Hume considered this distinction so obvious that he demurred 

from explaining it at any length; as he indicated in a summary explication in A Treatise of 

Human Nature (1739–40), impressions are felt, and ideas are thought. Nevertheless, he conceded 

that sometimes sleep, fever, or madness can produce ideas that approximate to the force of 

impressions, and some impressions can approach the weakness of ideas. But such occasions are 

rare. 

 

The distinction between impressions and ideas is problematic in a way that Hume did not notice. 

The impression (experience) of anger, for example, has an unmistakable quality and intensity. 

But the idea of anger is not the same as a “weaker” experience of anger. Thinking of anger no 

more guarantees being angry than thinking of happiness guarantees being happy. So there seems 

to be a difference between the impression of anger and the idea of anger that Hume’s theory does 

not capture. 

                                                             
211 H.C. Ezebuilo, Locke, Berkeley and Hume, 96. 

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All perceptions, whether impressions or ideas, can be either simple or complex.212 Whereas 

simple perceptions are not subject to further separation or distinction, complex perceptions are. 

To return to an example mentioned above, the perception of an apple is complex, insofar as it 

consists of a combination of simple perceptions of a certain shape, colour, texture, and aroma. It 

is noteworthy that, according to Hume, for every simple impression there is a simple idea that 

corresponds to it and differs from it only in force and vivacity, and vice versa. Thus, 

corresponding to the impression of red is the idea of red. This correlation does not hold true in 

general for complex perceptions. Although there is a correspondence between the complex 

impression of an apple and the complex idea of an apple, there is no impression that corresponds 

to the idea of Pegasus or to the idea of a unicorn; these complex ideas do not have a correlate in 

reality. Similarly, there is no complex idea corresponding to the complex impression of, say, an 

extensive vista of the city of Rome. 

 

Because the formation of every simple idea is always preceded by the experience of a 

corresponding simple impression, and because the experience of every simple impression is 

always followed by the formation of a corresponding simple idea, it follows, according to Hume, 

that simple impressions are the causes of their corresponding simple ideas.213 

 

There are two kinds of impressions: those of sensation and those of reflection. Regarding the 

former, Hume was of the opinion that sensation “arises in the soul originally from unknown 

causes.” Impressions of reflection arise from a complicated series of mental operations. First, one 

experiences impressions of heat or cold, thirst or hunger, pleasure or pain; second, one forms 

corresponding ideas of heat or cold, thirst or hunger, pleasure or pain; and third, one’s reflection 

on these ideas produces impressions of “desire and aversion, hope and fear.” 

 

Because the faculty of imagination can divide and assemble disparate ideas at will, 

some explanation is needed for the fact that people tend to think in regular and predictable 

patterns. Hume said that the production of thoughts in the mind is guided by three principles:214 

resemblance, contiguity, and cause and effect. Thus, people who think of one idea are likely to 

think of another idea that resembles it; their thought is likely to run from red to pink to white or 

from dog to wolf to coyote. Concerning contiguity, people are inclined to think of things that are 

next to each other in space and time. Finally, and most importantly, people tend to create 

associations between ideas of things that are causally related. The ideas of fire and smoke, parent 

and child, and disease and death are connected in the mind for that reason. 

 

                                                             
212https://www.britannica.com/biography/david-hume/ 
213 Ibid. 
214 Ibid. 

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Hume used the principle of resemblance for another purpose: to explain the nature of general 

ideas. He held that there are no abstract ideas, and he affirmed that all ideas are particular. Some 

of them, however, function as general ideas—i.e., ideas that represent many objects of a certain 

kind—because they incline the mind to think of other ideas that they resemble. 

 

11.7.2 Relations of ideas and matters of fact 

 

According to Hume, the mind is capable of apprehending two kinds of proposition or truth: those 

expressing “relations of ideas” and those expressing “matters of fact.”215 The former can be 

intuited—i.e., seen directly—or deduced from other propositions. That a is identical with a, 

that b resembles c, and that d is larger than e are examples of propositions that are intuited. The 

negations of true propositions expressing relations of ideas are contradictory. Because the 

propositions of arithmetic and algebra are exclusively about relations of ideas, according to 

Hume, those disciplines are more certain than others. In the Treatise, Hume said that geometry is 

not quite as certain as arithmetic and algebra, because its original principles derive from 

sensation, and about sensation there can never be absolute certainty. He revised his views later, 

however, and, in An Enquiry Concerning Human Understanding (1748), he put geometry on an 

equal footing with the other mathematical sciences.216 

 

Unlike propositions about relations of ideas, propositions about matters of fact are known only 

through experience. By far the most important of such propositions are those that express or 

presuppose causal relations—e.g., “Fire causes heat” and “A moving billiard ball communicates 

its motion to any stationary ball it strikes.” But how is it possible to know through experience 

that one kind of object or event causes another? What kind of experience would justify such a 

claim? 

 

11.7.3 Cause and effect 

 

Hume observed that the idea of causation contains three components: contiguity (i.e., near 

proximity) of time and place, temporal priority of the cause, and a more mysterious component, 

which he called “necessary connection.”217 In other words, when one says that x is a cause of y, 

one means that instances of x and instances of y are always near each other in time and space, 

that instances of x occur before instances of y, and that there is some connection between x’s 

and y’s that makes it necessary that an instance of y occurs if an instance of x does. 

 

                                                             
215https://www.britannica.com/topic/relation-logic-and-mathematics/ 
216 D. Hume, Enquiry Concerning Human Understanding and Concerning the Principles of Morals (Oxford: 
Clarendon Press, 1975). 
217 H.C. Ezebuilo, Locke, Berkeley and Hume, 99. 

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96 
 

It is easy to explain the origin in experience of the first two components of the idea of causation. 

In past experience, all events consisting of a moving billiard ball striking a stationary one were 

quickly followed by events consisting of the movement of the formerly stationary ball. In 

addition, the first sort of event always preceded the second and never the reverse. But whence the 

third component of the idea of causation, whereby one thinks that the striking of the stationary 

ball somehow necessitates that it will move? That necessity has never been seen or otherwise 

directly observed in past experience, as have the contiguity and temporal order of the striking 

and moving of billiard balls. 

 

It is important to note that were it not for the idea of necessary connection, there would be no 

reason to believe that a currently observed cause will produce an unseen effect in the future or 

that a currently observed effect was produced by an unseen cause in the past, for the mere fact 

that past instances of the cause and the effect were contiguous and temporally ordered in a 

certain way does not logically imply that present and future instances will display the same 

relations. Such an inference could be justified only if one assumed a principle such as “instances, 

of which we have had no experience, must resemble those, of which we have had experience, 

and that the course of nature continues always uniformly the same.” The problem with that 

principle is that it stands in need of justification, and the only possible justification is question-

begging. That is, one could argue that present and future experience will resemble past 

experience, because in the past, present and future experience resembled past experience. But 

that argument clearly assumes what it sets out to prove. 

 

Hume offered a “skeptical solution” of the problem of the origin of the idea of necessary 

connection. According to him, it arises from the feeling of “determination” that is created in the 

mind when it experiences the first member of a pair of events that it is long accustomed to 

experiencing together.218 When the mind observes the moving billiard ball striking the stationary 

one, it is moved by force of habit and custom to form an idea of the movement of the stationary 

ball—i.e., to believe that the stationary ball will move. The feeling of being “carried along” in 

this process is the impression from which the idea of necessary connection is derived. 

 

Hume’s solution is “skeptical” in the sense that, though it accounts for the origins of the idea of 

necessary connection, it does not make the causal inferences any more rational than they were 

before. The solution explains why we are psychologically compelled to form beliefs about future 

effects and past causes, but it does not justify those beliefs logically. It remains true that our 

only evidence for these beliefs is our past experience of contiguity and temporal precedence. 

“All inferences from experience, therefore, are effects of custom, not of reasoning.” Thus it is 

that custom, not reason, is the great guide of life. 

 

 

                                                             
218 Ibid. 

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11.7.4 Substance 

 

From the time of Plato, one of the most basic notions in philosophy has been “substance”—that 

whose existence does not depend upon anything else. For Locke, the substance of an object is the 

hidden “substratum” in which the object’s properties inhere and on which they depend for their 

existence. One of the reasons for Hume’s importance in the history of philosophy is that he 

rejected that notion. In keeping with his strict empiricism, he held that the idea of substance, if it 

answers to anything genuine, must arise from experience.219 But what kind of experience can 

that be? By its proponents’ own definition, substance is that which underlies an object’s 

properties, including its sensible properties; it is therefore in principle unobservable. Hume 

concluded, “We have therefore no idea of substance, distinct from that of a collection of 

particular qualities, nor have we any other meaning when we either talk or reason concerning 

it.”220 

 

Furthermore, the things that earlier philosophers had assumed were substances are in fact 

“nothing but a collection of simple ideas, that are united by the imagination, and have a 

particular name assigned to them.” Gold, to take Hume’s example, is nothing but the collection 

of the ideas of yellow, malleable, fusible, and so on. Even the mind, or the “self,” is only a “heap 

or collection of different perceptions united together by certain relations and supposed, though 

falsely, to be endowed with a perfect simplicity or identity.”221 That conclusion had important 

consequences for the problem of personal identity, to which Locke had devoted considerable 

attention, for if there is nothing to the mind but a collection of perceptions, then there is no self 

that perdures as the subject of those perceptions. Therefore, it does not make sense to speak of 

the subject of certain perceptions yesterday as the same self, or the same person, as the subject of 

certain perceptions today or in the future. There is no self or person there. 

 

11.8 Immanuel Kant 

 

Idealism is often defined as the view that everything that exists is mental. In other words, 

everything is either a mind or dependent for its existence on a mind. Immanuel Kant was not 

strictly an idealist according to that definition. His doctrine of “transcendental idealism” held that 

all theoretical (i.e., scientific) knowledge is a mixture of what is given in sense experience and 

what is contributed by the mind. The contributions of the mind are necessary conditions for 

having any sense experience at all. They include the spatial and temporal “forms” in which 

physical objects appear, as well as various extremely general features that together give the 

experience an intelligible structure. Those features are imposed when the mind, in the act of 

forming a judgment about experience, brings the content of experience under one of the “pure 

                                                             
219https://www.britannica.com/topic/substance-philosophy/ 
220 Ibid. 
221 Ibid. 

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98 
 

concepts of the understanding.222 Those concepts are unity, plurality, and totality; reality, 

negation, and limitation; inherence and subsistence, causality and dependence, 

and community (or reciprocity); and possibility, existence, and necessity. Among the more 

noteworthy of the mind’s contributions to experience is causality, which Hume asserted has no 

real existence.  

 

His idealism notwithstanding, Kant also believed that there exists a world independent of the 

mind and completely unknowable by it.223 That world consists of “things-in-themselves” 

(noumena), which do not exist in space and time and do not enter into causal relations. Because 

of his commitment to realism (minimal though it may have been), Kant was disturbed by 

Berkeley’s uncompromising idealism, which amounted to a denial of the existence of the 

external world. Kant found that doctrine incredible and rejected “the absurd conclusion that there 

can be appearance without anything that appears.”224 

 

Because Kant’s theory attributes to the mind many aspects of reality that earlier theories assumed 

are given in or derived from experience, it can be thought of as inverting the traditional relation 

in epistemology between the mind and the world. According to Kant, knowledge results not 

when the mind accommodates itself to the world but rather when the world conforms to the 

requirements of human sensibility and rationality. Kant compared his reorientation of 

epistemology to the Copernican revolution in astronomy, which placed the Sun rather than Earth 

at the centre of the universe. 

 

According to Kant, the propositions that express human knowledge can be divided into three 

kinds:225 (1) analytic a priori propositions, such as “All bachelors are unmarried” and “All 

squares have four sides,” (2) synthetic a posteriori propositions, such as “The cat is on the mat” 

and “It is raining,” and (3) what he called “synthetic a priori” propositions, such as “Every event 

has a cause.” Although in the last kind of proposition the meaning of the predicate term is not 

contained in the meaning of the subject term, it is nevertheless possible to know the proposition 

independently of experience, because it expresses a condition imposed by the forms of 

sensibility. Nothing can be an object of experience unless it is experienced as having causes and 

effects. Kant stated that the main purpose of his doctrine of transcendental idealism was to show 

how such synthetic a priori propositions are possible. 

 

Since human beings can experience the world only as a system that is bounded by space and time 

and completely determined by causal laws, it follows that they can have no theoretical (i.e., 

scientific) knowledge of anything that is inconsistent with such a realm or that by definition 

                                                             
222 I. Kant, Critique of Pure Reason (New York: Anchor Books, 1966).  
223 Ibid. 
224 Ibid. 
225 Ibid. 

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https://www.britannica.com/topic/a-priori-knowledge
https://www.britannica.com/topic/a-posteriori-knowledge
https://www.britannica.com/topic/synthetic-a-priori-proposition
https://www.merriam-webster.com/dictionary/predicate
https://www.merriam-webster.com/dictionary/synthetic


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exists independently of it—including God, human freedom, and the immortality of the soul. 

Nevertheless, belief in those ideas is justified, according to Kant, because each is a necessary 

condition of our conceiving of ourselves as moral agents. 

 

11.8.1 A Summary of Kant’s Epistemology 

Immanuel Kant (1724-1804) sought to bridge, to synthesize, the rationalist and empiricist 

traditions in epistemology. He did so in response to the skepticism of David Hume, whom he 

said had “awaken him from his dogmatic slumbers.” Kant agreed with the empiricists that 

concepts without perceptions are empty. Concepts/ideas alone cannot constitute knowledge. 

Innate ideas do not constitute knowledge. There must be experience(s) for there to be knowledge. 

However, Kant also agreed with the rationalists that perceptions without concepts are blind. 

Merely having experiences/perceptions also does not constitute knowledge. There must be some 

way in which the mind organizes/structures experience for there to be knowledge. 

Kant also held that it is true that all knowledge begins with experience. Without experience no 

knowledge takes place. Experience is the initiator of the process of attaining knowledge. Here he 

once again agrees with the empiricist affirmation of the necessity of experience in knowing. 

However, Kant also held that, it is not true that all knowledge arises from experience. Experience 

is not the sole source of knowledge. There must be “categories” by which experience is 

structured/understood for there to be knowledge. Here he agrees with the rationalists. 

Kant affirmed that the mind is active in the knowing process. The mind makes an active 

contribution to “the-world-as-it-is-known.” The world-as-it-is-known” (what Kant would call the 

phenomenal realm) conforms to the mind in the knowledge process, rather than the mind 

conforming to a world that has its own mind-independent structure/organization. Thus, 

knowledge has a profoundly subjective dimension (i.e. the mind) as well as an objective 

dimension (i.e. the world-as-it-is-in-itself; what Kant would call the noumenal realm). 

The mind contains “categories of understanding.” These categories are the ways in which the 

active mind forms or structures experience. For Kant, there were twelve of such categories, one 

of which was the category of causation/cause-and-effect. The active mind relates and 

understands experiences in terms of some event-experiences being causes, with other event-

experiences being their effects. 

Furthermore, Kant affirmed synthetic a-priori truths. These are truths that are universal and 

necessary, as a-priori truths are truths that are universal and necessary. Unlike universal and 

necessary truths that are analytically true (i.e. true in accordance with the meaning of concepts, 

but telling us nothing about the way the world is), Kant affirmed that some universal and 

necessary truths are synthetic – they tell us about the way the known world is. They are 

constitutive of the-world-as-it-is-known. 

Meanwhile, the basis of scientific knowledge is the fact that “every event has a cause.” Hume 

demonstrated that we cannot claim to know/justify this on the basis of empiricist assumptions. 

https://www.britannica.com/topic/immortality
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He held that “cause” is not a thing/fact out there in the world. Thus we can have no idea or 

knowledge of causal connections in reality.226 Causal attributions are merely a kind of mental 

habit. Now, Kant held that the statement “every event has a cause” is a universally and 

necessarily true statement – something that we do know. It is not a mere mental habit. But the 

truth of the statement is grounded in the ‘cause-category” within the mind that actively 

structures, universally and necessarily, all our experience of the world. Kant assumed that every 

human being, as a rational being, possesses and utilizes the same categories of understanding. As 

reason is the same in all rational beings, so in principle the proper exercise of reason will lead 

any and all persons to knowledge claims that are objectively and universally valid. 

It follows that we do not know reality as it might be “in itself” – apart from how our minds 

structure experience of “mind-independent reality.” We do not know noumena. We only know 

reality in terms of how our active minds structure/organize/form our experiences of mind-

independent reality. We only know phenomena.  

11.9 G.W.F. Hegel 

 

The positive views of the German idealist philosopher Georg Wilhelm Friedrich Hegel (1770–

1831) are notoriously difficult, and his epistemology is not susceptible of adequate summary 

within the scope of this book. Some of his criticisms of earlier epistemological views should be 

mentioned, however, since they helped to bring the modern era in philosophy to a close. 

In his Phenomenology of Spirit (1807),227 Hegel criticized traditional empiricist epistemology for 

assuming that at least some of the sensory content of experience is simply “given” to 

the mind and apprehended directly as it is, without the mediation of concepts. According to 

Hegel, there is no such thing as direct apprehension, or unmediated knowledge. Although Kant 

also held that empirical knowledge necessarily involves concepts (as well as the mentally 

contributed forms of space and time), he nevertheless attributed too large a role to the given, 

according to Hegel. 

Another mistake of earlier epistemological theories—both empiricist and rationalist—is the 

assumption that knowledge entails a kind of “correspondence” between belief and reality. The 

search for such a correspondence is logically absurd, Hegel argued, since every such search must 

end with some belief about whether the correspondence holds, in which case one has not 

advanced beyond belief.228 In other words, it is impossible to compare beliefs with reality, 

because the experience of reality is always mediated by beliefs. One cannot step outside belief 

altogether. For Hegel, the Kantian distinction between the phenomena of experience and the 

unknowable thing-in-itself is an instance of that absurdity. 

 

                                                             
226 H.C. Ezebuilo, “Locke, Berkeley and Hume: A Brief Survey of Empiricism,” International Journal of Research in 
Education, Humanities and Commerce 1(2), (2020). 
227https://www.britannica.com/biography/george-wilhelm-friedrich-hegel/ 
228 Ibid. 

https://www.britannica.com/biography/Georg-Wilhelm-Friedrich-Hegel
https://www.britannica.com/biography/Georg-Wilhelm-Friedrich-Hegel
https://www.merriam-webster.com/dictionary/criticisms
https://www.britannica.com/topic/mind
https://www.merriam-webster.com/dictionary/apprehension
https://www.merriam-webster.com/dictionary/empirical
https://www.britannica.com/topic/correspondence-theory-of-truth
https://www.britannica.com/topic/belief


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CHAPTER TWELVE 

THE HISTORY OF EPISTEMOLOGY: CONTEMPORARY PHILOSOPHY 

 

12.1 Introductory Discourse 

Contemporary Philosophy began in the late 19th and early 20th centuries. Much of what sets it 

off from modern Philosophy is its explicit criticism of the modern tradition and sometimes its 

apparent indifference to it. There are two basic strains of Contemporary Philosophy: Continental 

Philosophy, which is the Philosophical style of western European Philosophers, and analytic 

Philosophy (also called Anglo-American Philosophy), which includes the work of many 

European Philosophers who immigrated to Britain, the United States, and Australia shortly 

before World War II. 

 

12.2 Analytic Epistemology 

 

Analytic Philosophy, the prevailing form of philosophy in the Anglo-American world since the 

beginning of the 20th century, has its origins in symbolic logic (or formal logic) on the one hand 

and in British empiricism on the other. Some of its most important contributions have been made 

in areas other than epistemology, though its epistemological contributions also have been of the 

first order. Its main characteristics have been the avoidance of system building and a 

commitment to detailed, piecemeal analyses of specific issues. Within that tradition there have 

been two main approaches: a formal style deriving from logic and an informal style 

emphasizing ordinary language. Ludwig Wittgenstein (1889–1951) can be situated in both 

groups—his early work, including the Tractatus Logico-Philosophicus (1921), belonging to the 

former tradition and his later work, including the posthumously published Philosophical 

Investigations (1953) and On Certainty (1969), to the latter. 

 

Perhaps the most distinctive feature of analytic Philosophy is its emphasis on the role 

that language plays in the creation and resolution of philosophical problems. Those problems, it 

is said, arise through misunderstandings of the forms and uses of everyday language. 

Wittgenstein said in that connection, “Philosophy is a battle against the bewitchment of the 

intelligence by means of language.”229 The adoption at the beginning of the 20th century of the 

idea that Philosophical problems are in some important sense linguistic (or conceptual), a 

hallmark of the analytic approach, has been called the “linguistic turn.” 

 

 

12.3 Commonsense Philosophy, Logical Positivism, and Naturalized Epistemology 

 

Three of the most-notable schools of thought in analytic philosophy are commonsense 

philosophy, logical positivism, and naturalized epistemology. Commonsense philosophy is the 

                                                             
229 Cf. J. Omoregbe, Epistemology: A Systematic and Historical Study (Lagos: Joja Press, 2005,), 19-20. 

https://www.merriam-webster.com/dictionary/criticism
https://www.britannica.com/topic/continental-philosophy
https://www.britannica.com/topic/continental-philosophy
https://www.britannica.com/topic/analytic-philosophy
https://www.britannica.com/topic/analytic-philosophy
https://www.britannica.com/event/World-War-II
https://www.britannica.com/topic/analytic-philosophy
https://www.britannica.com/topic/formal-logic
https://www.britannica.com/topic/empiricism
https://www.britannica.com/topic/logic
https://www.britannica.com/topic/ordinary-language-analysis
https://www.britannica.com/biography/Ludwig-Wittgenstein
https://www.britannica.com/topic/language
https://www.britannica.com/topic/philosophy-of-common-sense
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name given to the epistemological views of Moore, who attempted to defend what he called the 

“commonsense” view of the world against both skepticism and idealism. That view, according to 

Moore, comprises a number of propositions—such as the propositions that Earth exists, that it is 

very old, and that other persons now exist on it—that virtually everybody knows with certainty 

to be true. Any Philosophical theory that runs counter to the commonsense view, therefore, can 

be rejected out of hand as mistaken and skepticism and idealism fail under this category. Thus, 

Wittgenstein rejected skepticism and idealism, though for very different reasons. For him, those 

positions are based on simplistic misunderstandings of epistemic concepts, misunderstandings 

that arise from a failure to recognize the rich variety of ways in which Epistemic terms 

(including words such as belief, knowledge, certainty, justification, and doubt) are used in 

everyday situations. In On Certainty, Wittgenstein contrasted the concepts of certainty and 

knowledge, arguing that certainty is not a “surer” form of knowledge but the necessary backdrop 

against which the “language games” of knowing, doubting, and inquiring take place. As that 

which “stands fast for all of us,” certitude is ultimately a kind of action: “Action lies at the 

bottom of the language game.”230 

The doctrines associated with logical positivism (also called logical empiricism) was developed 

originally in the 1920s and 1930s by a group of Philosophers and Scientists known as the Vienna 

Circle. Logical positivism became one of the dominant schools of philosophy in England with 

the publication of Language, Truth, and Logic by A.J. Ayer (1910–89). Among the most 

influential theses put forward by the logical positivists was the claim that in order for a 

proposition with empirical content—i.e., one that purports to say something about the world—to 

be meaningful, or cognitively significant, it must be possible, at least in principle, to verify the 

proposition through experience.231 Because many of the utterances of traditional philosophy 

(especially metaphysical utterances, such as “God exists”) are not empirically verifiable even in 

principle, they are, according to the logical positivists, literally nonsense. In their view, the 

only legitimate function of Philosophy is conceptual analysis—i.e., the logical clarification of 

concepts, especially those associated with natural science (e.g., probability and causality).  

In his 1950 essay “Two Dogmas of Empiricism,” Quine launched an attack upon the traditional 

distinction between analytic statements, which were said to be true by virtue of the meanings of 

the terms they contain, and synthetic statements, which were supposed to be true or false by 

virtue of certain facts about the world.232 He argued powerfully that the difference is one of 

degree rather than kind. In his later work, Word and Object (1960), Quine developed a doctrine 

known as naturalized Epistemology.233 According to that view, epistemology has no normative 

function. That is, it does not tell people what they ought to believe, instead, it only legitimate 

role is to describe the way knowledge, especially scientific knowledge, is actually obtained. In 

                                                             
230 L. Wittgenstein, On Certainty, Denis Paul and G.E.M. Anscombe (trans.), (London: Basil Blackwell, 1969), 51. 
231 Cf. J. Omoregbe, Epistemology, 19. 
232 https://www.britannica.com/topic/two-dogmas-of-empiricism/ 
233 W.V.O. Quine, Word and Object, 1960, https://mitpress.mit.edu/books/word-and-objects/ 

https://www.britannica.com/biography/G-E-Moore
https://www.britannica.com/topic/skepticism
https://www.britannica.com/topic/idealism
https://www.merriam-webster.com/dictionary/comprises
https://www.britannica.com/topic/logical-positivism
https://www.britannica.com/topic/Vienna-Circle
https://www.britannica.com/topic/Vienna-Circle
https://www.britannica.com/biography/A-J-Ayer
https://www.britannica.com/topic/metaphysics
https://www.merriam-webster.com/dictionary/legitimate
https://www.merriam-webster.com/dictionary/conceptual
https://www.britannica.com/science/probability
https://www.britannica.com/topic/causation
https://www.britannica.com/topic/Two-Dogmas-of-Empiricism
https://www.merriam-webster.com/dictionary/synthetic
https://www.britannica.com/biography/Willard-Van-Orman-Quine
https://www.britannica.com/topic/naturalized-epistemology


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effect, its function is to describe how present science arrives at the beliefs accepted by the 

scientific community. 

The Epistemological interests of analytic Philosophers in the first half of the 20th century were 

largely focused on the relationship between knowledge and perception. The major figures in that 

period were Russell, Moore, H.H. Price (1899–1984), C.D. Broad (1887–1971), Ayer, and H. 

Paul Grice (1913–88). Although their views differed considerably, they were all advocates of a 

general doctrine known as sense-data theory. 

The technical term sense-data is sometimes explained by means of examples. If one is 

hallucinating and sees pink rats, one is having a certain visual sensation of rats of a certain 

colour, though there are no real rats present. The sensation is what is called a “sense-datum.” The 

image one sees with one’s eyes closed after looking fixedly at a bright light (an afterimage) is 

another example. Even in cases of normal vision. However, one can be said to be apprehending 

sense-data. For instance, when one looks at a round penny from a certain angle, the penny will 

seem to have an elliptical shape. In such a case, there is an elliptical sense-datum in one’s visual 

field, though the penny itself continues to be round. The last example was held by Broad, Price, 

and Moore to be particularly important, for it seems to make a strong case for holding that one 

always perceives sense-data, whether one’s perception is normal or abnormal. 

In each of those examples, according to defenders of sense-data theory, there is something of 

which one is “directly” aware, meaning that one’s awareness of it is immediate and does not 

depend on any inference or judgment. A sense-datum is thus frequently defined as an object of 

direct perception. According to Broad, Price, and Ayer, sense-data differ from physical objects in 

that they always have the properties they appear to have; that is, they cannot appear to have 

properties they do not really have. The problem for the Philosopher who accepts sense-data is 

how, on the basis of such private sensations, one can be justified in believing that there are 

physical objects that exist independently of one’s perceptions. Russell in particular tried to show 

that knowledge of the external world could be logically constructed out of sense-data.234 

Sense-data theory was criticized by proponents of the so-called theory of appearing, who claimed 

that the arguments for the existence of sense-data are invalid. From the very fact that a penny 

looks elliptical from a certain perspective, it does not follow that there must exist a separate 

entity, distinct from the penny itself, that has the property of being elliptical. To assume that it 

does is simply to misunderstand how common perceptual situations are described. 

The theory of appearing was in turn rejected by many philosophers, who held that it failed to 

provide an adequate account of the epistemological status of illusions and other visual anomalies. 

The aim of those thinkers was to give a coherent account of how knowledge is possible given the 

                                                             
234 B. Russell, Our Knowledge of the External World, (1914), https://www.routledge.com. 

https://www.merriam-webster.com/dictionary/community
https://www.merriam-webster.com/dictionary/analytic
https://www.britannica.com/topic/perception
https://www.britannica.com/biography/H-H-Price
https://www.britannica.com/topic/sense-data
https://www.britannica.com/science/vision-physiology
https://www.merriam-webster.com/dictionary/inference
https://www.merriam-webster.com/dictionary/illusions
https://www.merriam-webster.com/dictionary/anomalies
https://www.merriam-webster.com/dictionary/coherent


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existence of sense-data and the possibility of perceptual error. The two main types of theories 

they developed are realism and phenomenalism. 

 

12.4 Realist Epistemology 

 

Realism is both an Epistemological and a Metaphysical doctrine. In its Epistemological aspect, 

Realism claims that at least some of the objects apprehended through perception are “public” 

rather than “private.” In its Metaphysical aspect, realism holds that at least some objects of 

perception exist independently of the mind. It is especially the second of those principles that 

distinguishes Realists from Phenomenalists. 

 

Realists believe that an intuitive, commonsense distinction can be made between two classes of 

entities perceived by human beings. One class, typically called “mental,” consists of things like 

headaches, thoughts, pains, and desires. The other class, typically called “physical,” consists of 

things such as tables, rocks, planets, human beings, animals and certain physical phenomena 

such as rainbows, lightning, and shadows. According to Realist Epistemology, mental entities are 

private in the sense that each of them is apprehensible by one person only. Although more than 

one person can have a headache or feel pain, for example, no two people can have the very same 

headache or feel the very same pain. In contrast, physical objects are public: more than one 

person can see or touch the same chair. 

 

Realists also believe that whereas physical objects are mind-independent, mental objects are not. 

To say that an object is mind-independent is just to say that its existence does not depend on its 

being perceived or experienced by anyone. Thus, whether or not a particular table is being seen 

or touched by someone has no effect upon its existence. Even if no one is perceiving it, it still 

exists (other things being equal). But this is not true of the mental. According to Realists, if no 

one is having a headache, then it does not make sense to say that a headache exists. A headache 

is thus mind-dependent in a way in which tables, rocks, and shadows are not. 

 

Traditional Realist theories of knowledge thus begin by assuming the public-private distinction, 

and most realists also assume that one does not have to prove the existence of mental 

phenomena. Each person is directly aware of such things, and there is no special “problem” 

about their existence. However, that is not true of physical phenomena. As the existence of 

visual aberrations, illusions, and other anomalies shows, one cannot be sure that in any 

perceptual situation one is apprehending physical objects. All that people can be sure of is that 

they are aware of something, an appearance of some sort—say, of a bent stick in water and 

whether that appearance corresponds to anything actually existing in the external world is an 

open question. 

 

https://www.britannica.com/topic/phenomenalism
https://www.britannica.com/topic/realism-philosophy
https://www.merriam-webster.com/dictionary/metaphysical
https://www.britannica.com/topic/mind
https://www.britannica.com/topic/intuition
https://www.britannica.com/topic/existence
https://www.merriam-webster.com/dictionary/aberrations


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In his work Foundations of Empirical Knowledge, Ayer called the difficulty “the egocentric 

predicament.”235 When a person looks at what he thinks is a physical object, such as a chair, 

what he is directly apprehending is a sense-datum, a certain visual appearance, such an 

appearance seems to be private to that person; it seems to be something mental and not publicly 

accessible. What, then, justifies the individual’s belief in the existence of supposedly external 

objects—that is, physical entities that are public and exist independently of the mind? This 

however led the Realists to develop two main responses to the challenge: direct (or “naive”) 

realism and representative realism, also called the “causal theory.” 

In contrast to traditional realism, direct realism holds that physical objects themselves are 

perceived “directly.” That is, what one immediately perceives is the physical object itself (or a 

part of it). Thus, there is no problem about inferring the existence of such objects from the 

contents of one’s perception. Some direct realists, such as Moore and his followers, continued to 

accept the existence of sense-data. Unlike traditional realists, they held that, rather than mental 

entities, sense-data might be physical parts of the surface of the perceived object itself. Other 

direct realists, rejected sense-data theory altogether, claiming that the surfaces of physical objects 

are normally directly observed. Thompson Clarke (1928–2012) went beyond Moore in arguing 

that normally the entire physical object, rather than only its surface, is perceived directly.236 

All such views have trouble explaining perceptual problems or anomalies. Indeed, it was because 

of such difficulties that Moore, in his last published paper, “Visual Sense-Data” (1957), 

abandoned direct realism. He held that because the elliptical sense-datum one perceives when 

one looks at a round coin cannot be identical with the coin’s circular surface, for one cannot be 

seeing the coin directly.237 Hence, one cannot have direct knowledge of physical objects. 

Additionally, the theory of representative realism is in essence an old view; its best-known 

exponent in modern philosophy was Locke. It is also sometimes called “the scientific theory” 

because it seems to be supported by findings in optics and physics. Like most forms of realism, 

representative realism holds that the direct objects of perception are sense-data (or their 

equivalents). What it adds is a scientifically grounded causal account of the origin of sense-data 

in the stimulation of sense organs and the operation of the central nervous system. Thus, the 

theory would explain visual sense-data as follows. Light is reflected from 

an opaque surface, traverses an intervening space, and, if certain standard conditions are met, 

strikes the retina, where it activates a series of nerve cells, including the rods and cones, the 

bipolar cells, and the ganglion cells of the optic nerve, eventually resulting in an event in the 

brain consisting of the experience of a visual sense-datum, that is, “seeing.”238 

                                                             
235 A.J. Ayer, The Foundations of Empirical Knowledge, (1940), https://philpapers.org. 
236 https://www.britannica.com/biography/thmpson-clarke/ 
237 G.E. Moore, “Visual Sense-Data,” (1958), https://www,britannica.com/topic/visual-sense-data/ 
238 https://www.britannica.com/science/light/ 

https://www.britannica.com/topic/The-Foundations-of-Empirical-Knowledge
https://www.britannica.com/topic/belief
https://www.britannica.com/topic/direct-realism
https://www.britannica.com/topic/direct-realism
https://www.britannica.com/biography/G-E-Moore
https://www.britannica.com/topic/philosophy
https://www.britannica.com/science/optics
https://www.britannica.com/science/physics-science
https://www.britannica.com/science/human-nervous-system
https://www.britannica.com/science/light
https://www.merriam-webster.com/dictionary/opaque
https://www.merriam-webster.com/dictionary/traverses
https://www.britannica.com/science/retina
https://www.britannica.com/science/rod-retinal-cell
https://www.britannica.com/science/cone-retinal-cell
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Given an appropriate normal causal connection between the original external object and the 

sense-datum, representative realists assert that the sense-datum will accurately represent the 

object as it really is. Visual illusion is explained in various ways but usually as the result of 

some anomaly in the causal chain that gives rise to distortions and other types of aberrant visual 

phenomena. 

Representative realism is thus a theory of indirect perception, because it holds that human 

observers are directly aware of sense-data and only indirectly aware of the physical objects that 

cause those data in the brain. The difficulty with representative realism is that since people 

cannot compare the sense-datum that is directly perceived with the original object, they can 

never be sure that the former gives an accurate representation of the latter, and, therefore, they 

cannot know whether the real world corresponds to their perceptions. They are still confined 

within the circle of appearance after all. It thus seems that neither version of realism 

satisfactorily solves the problem with which it began. 

 

12.5 Continental/Phenomenological Epistemology 

 

In Epistemology, Continental Philosophers during the first quarter of the 20th century were 

preoccupied with the problem of overcoming the apparent gap between the knower and the 

known. 

 

In light of the difficulties faced by realist theories of perception, some philosophers, so-called 

phenomenalists, proposed a completely different way of analyzing the relationship between 

perception and knowledge. In particular, they rejected the distinction between independently 

existing physical objects and mind-dependent sense-data. They claimed that the very notion of 

independent existence is nonsense—because human beings have no evidence for it—or what is 

meant by “independent existence” must be understood in such a way as not to go beyond the sort 

of perceptual evidence human beings do or could have for the existence of such things.239 In 

effect, phenomenalists challenged the cogency of the intuitive ideas that the ordinary person 

supposedly has about independent existence. 

All variants of phenomenalism are strongly “verificationist.” That is, they wish to maintain their 

claims that the purported external world must be capable of verification, or confirmation. Their 

commitment entails that no such claim can assert the existence of, or otherwise make reference 

to, anything that is beyond the realm of possible perceptual experience. 

Therefore, phenomenalists have tried to analyze in wholly perceptual terms what it means to say 

that a particular object—say, a tomato—exists.240 Any such analysis, they claim, must begin by 

                                                             
239 https://www.britannica.com/topic/phenomenology/ 
240 Ibid. 

https://www.merriam-webster.com/dictionary/illusion
https://www.merriam-webster.com/dictionary/anomaly
https://www.britannica.com/topic/reality
https://www.britannica.com/topic/appearance
https://www.britannica.com/topic/dualism-philosophy
https://www.britannica.com/topic/dualism-philosophy
https://www.britannica.com/topic/perception
https://www.britannica.com/topic/evidence-law
https://www.britannica.com/topic/external-world


107 
 

deciding what sort of an object a tomato is. In their view, a tomato is first of all something that 

has certain perceptible properties, including a certain size, weight, colour, and shape. If one were 

to abstract the set of all such properties from the object, nothing would be left over—there would 

be no presumed Lockean “substratum” that supports those properties and that itself is 

unperceived. Hence, there is no evidence in favour of such an unperceivable feature, and no 

reference to it is needed in explaining what a tomato or any other so-called physical object is. 

To talk about any existent object is to talk about a collection of perceivable features localized in 

a particular portion of space-time. Accordingly, to say that a tomato exists is to describe either a 

collection of properties that an observer is actually perceiving or a collection that such an 

observer would perceive under certain specified conditions. To say, for instance, that a tomato 

exists in the next room is to say that if one went into that room, one would see a familiar reddish 

shape, one would obtain a certain taste if one bit into it, and one would feel something soft and 

smooth if one touched it. Thus, to speak about the tomato’s existing unperceived in the next 

room does not entail that it is unperceivable. In principle, everything that exists is perceivable. 

Therefore, the notion of existing independently of perception has been misunderstood or 

mischaracterized by both philosophers and non-philosophers.241 Once it is understood that 

objects are merely sets of properties and that such properties are in principle always perceivable, 

the notion that there is some sort of unbridgeable gap between people’s perceptions and the 

objects they perceive is seen to be just a mistake. 

In the phenomenalist view, perceptual error is explained in terms of coherence and 

predictability.242 To say with truth that one is perceiving a tomato means that one’s present set of 

perceptual experiences and an unspecified set of future experiences will “cohere” in certain 

ways. That is, if the object being looked at is a tomato, then one can expect that if one touches, 

tastes, and smells it, one will experience a recognizable grouping of sensations. If the object in 

the visual field is hallucinatory, then there will be a lack of coherence between what one touches, 

tastes, and smells. One might, for example, see a red shape but will not be able to touch or taste 

anything. 

The theory is generalized to include what others would touch, see, and hear as well, so that what 

the realists call “public” will also be defined in terms of the coherence of perceptions. A so-

called physical object is public if the perceptions of many persons cohere or agree; otherwise, it 

is not. That explains why a headache is not a public object. In similar fashion, a so-

called physical object will be said to have an independent existence if expectations of future 

perceptual experiences are borne out. If tomorrow, or the day after, one has perceptual 

experiences similar to those one had today, then one can say that the object being perceived has 

an independent existence. The phenomenalist thus attempts, without positing the existence of 

                                                             
241 Ibid. 
242 Ibid. 

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anything that transcends possible experience, to account for all the facts that the realist wishes to 

explain. 

Criticisms of phenomenalism have tended to be technical. Generally speaking, realists have 

objected to it on the ground that it is counterintuitive to think of physical objects such as 

tomatoes as being sets of actual or possible perceptual experiences. Realists argue that one does 

have such experiences, or under certain circumstances would have them, because there is an 

object out there that exists independently and is their source. Phenomenalism, contention implies 

that if no perceivers existed, then the world would contain no objects, and that is surely 

inconsistent both with what ordinary persons believe and with the known scientific fact that all 

sorts of objects existed in the universe long before there were any perceivers. But supporters 

deny that phenomenalism carries such an implication, and the debate about its merits remains 

unresolved. 

 

12.5.1 Edmund Husserl 

 

The German Philosopher Edmund Husserl (1859–1938) thought that the standard 

epistemological theories of his day lacked insight because they did not focus on the objects of 

knowledge as they are actually experienced by human beings. To emphasize that reorientation of 

thinking, he adopted the slogan, “To the things themselves.” Philosophers needed to recover a 

sense of what is given in experience itself, and that could be accomplished only through a careful 

description of experiential phenomena. Thus, Husserl called his Philosophy 

“Phenomenology,”243 which was to begin as a purely descriptive science and only later to ascend 

to a theoretical, or “transcendental,” one. 

 

According to Husserl, the philosophies of Descartes and Kant presupposed a gap between the 

aspiring knower and what is known, one that made claims to knowledge of the external world 

dubious and in need of justification. Those presuppositions violated Husserl’s belief that 

philosophy, as the most fundamental science, should be free of presuppositions. Thus, he held 

that it is illegitimate to assume that there is a problem about our knowledge of the external world 

prior to conducting a completely presuppositionless investigation of the matter.244 The device 

that Husserl used to remove such presuppositions was the epochē (Greek: “withholding” or 

“suspension”), originally a principle of ancient Greek Skepticism but in Husserl’s philosophy a 

technique of “bracketing,” or removing from consideration, not only all traditional Philosophical 

theories but also all commonsensical beliefs so that pure phenomenological description can 

proceed.245 

 

                                                             
243 Cf. https://www.britannica.com/topic/phenomenology/ 
244 Cited in J. Omoregbe, Epistemology: A Systematic and Historical Study (Lagos: Joja Press, 2005,), 52-54. 
245 Ibid. 

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The epochē was just one of a series of the so-called transcendental reductions that Husserl 

proposed in order to ensure that he was not presupposing anything. One of those reductions 

supposedly gave one access to “the transcendental ego,” or “pure consciousness.”246 Although 

one might expect Phenomenology then to describe the experience or contents of this ego, Husserl 

instead aimed at “eidetic reduction”—that is, the discovery of the essences of various sorts of 

ideas, such as redness, surface, or relation.247 All of those moves were part of Husserl’s project 

of discovering a perfect methodology for Philosophy, one that would ensure absolute certainty. 

 

Husserl’s transcendental ego seemed very much like the Cartesian mind that thinks of a world 

but has neither direct access to nor certainty of it. Accordingly, Husserl attempted to overcome 

the apparent gap between the ego and the world—the very thing he had set out to destroy or to 

bypass in earlier works, because the transcendental ego seems to be the only genuinely 

existent consciousness, Husserl was also was faced with the task of overcoming the problem 

of solipsism. 

 

12.5.2 Martin Heidegger 

 

Many of Husserl’s followers, including his most famous student, Martin Heidegger (1889–1976), 

recognized that something had gone radically wrong with the original direction of 

Phenomenology. According to Heidegger’s diagnosis, the root of the problem was Husserl’s 

assumption that there is an “Archimedean point” of human knowledge. For him, there is no 

such ego detached from the world and filled with ideas or representations. According to 

Heidegger in one of his writing  Being and Time (1927), Heidegger returned to the original 

formulation of the phenomenological project as a return to the things themselves. Thus, in 

Heidegger’s approach, all transcendental reductions are abandoned. What he claimed to discover 

is that human beings are inherently world-bound.248 The world does not need to be derived; it is 

presupposed by human experience. In their pre-reflective experience, humans inhabit a 

sociocultural environment in which the primordial kind of cognition is practical and communal, 

not theoretical or individual (“egoistic”).249 Human beings interact with the things of their 

everyday world (Lebenswelt) as a workman interacts with his tools; they hardly ever approach 

the world as a Philosopher or Scientist would. The theoretical knowledge of a Philosopher is a 

derivative and specialized form of cognition, and the major mistake of Epistemology from 

Descartes to Kant to Husserl was to treat Philosophical knowledge as a paradigm of all 

knowledge. 

                                                             
246 Ibid. 
247 Ibid. 
248 M. Heidegger, Being and Time, Joan Stambaugh (trans.). (New York: Blackwell, 1996), 311. 
249 Ibid. 

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Notwithstanding Heidegger’s insistence that a human being is something that inhabits a world, 

he marked out human reality as ontologically special. He called that reality Dasein—the being, 

apart from all others, which is “present” to the world.250 Thus, as in Husserl’s phenomenology, 

a cognitive being takes pride of place in Heidegger’s Philosophy. 

12.5.3 Maurice Merleau-Ponty and Jean-Paul Sartre. 

In France the principal representative of Phenomenology in the mid twentieth century 

was Maurice Merleau-Ponty(1908-1961).251 Merleau-Ponty rejected Husserl’s bracketing of the 

world, arguing that human experience of the world is primary, a view he encapsulated in the 

phrase “the primacy of perception.”252 He furthermore held that dualistic analyses of knowledge, 

best exemplified by traditional Cartesian mind-body dualism, are inadequate. In fact, in his view, 

no conceptualization of the world can be complete, because human cognitive experience requires 

a body and the body a position in space, human experience is necessarily perspectival and thus 

incomplete.253 Although, humans experience a material being as a multidimensional object, part 

of the object always exceeds their cognitive grasp just because of their limited perspective. 

The epistemological views of Jean-Paul Sartre (1905–80) are similar in some respects to those of 

Merleau-Ponty. Both Philosophers rejected Husserl’s transcendental reductions and both thought 

of human reality as “being-in-the-world,” but Sartre’s views have Cartesian elements that 

were anathema to Merleau-Ponty. Sartre distinguished between two basic kinds of being.254 

Being-in-itself (en soi) is the inert and determinate world of non-human existence. Over and 

against it is being-for-itself (pour soi), which is the pure consciousness that defines human 

reality. 

Later Continental Philosophers attacked the entire Philosophical tradition from Descartes to the 

twentieth century for its explicit or implicit dualisms. Being/non-being, mind/body, 

knower/known, ego/world, being-in-itself/being-for-itself are all variations of a pattern of 

thinking that the Philosophers of the last third of the twentieth century tried to undermine. The 

Structuralist Michel Foucault (1926–84), for example, wrote extensive historical studies in an 

attempt to demonstrate that all concepts are historically conditioned and that many of the most 

important ones serve the political function of controlling people rather than any purely cognitive 

purpose.255 Jacques Derrida (1930–2004) claimed that all dualisms are value-laden and 

                                                             
250 Ibid. 
251https://www.britannica.com/biography/maurice-merleau-ponty/ 
252 M. Merleau-Ponty, Phenomenology of Perception, Donald Landes (trans.), (London: Routledge, 1965), 298. 
253 Ibid. 
254https://www.britannica.com/biography/jean-paul-sartre/ 
255 Michael Foucault, (1969), The Archaeology of Knowledge, A.M. Sheridan Smith (trans.), London and New York: 
Routledge, 2002), 117-118. 

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indefensible.256 His technique of deconstruction aimed to show that every 

Philosophical dichotomy is incoherent because whatever can be said about one term of the 

dichotomy can also be said of the other. 

Dissatisfaction with the Cartesian Philosophical tradition can also be found in the thought of the 

American Pragmatist, John Dewey (1859–1952). He directly challenged the idea that knowledge 

is primarily theoretical.257 Experience, he argued, consists of an interaction between living 

beings and their environment. Knowledge is not a fixed apprehension of something but a process 

of acting and being acted upon. Richard Rorty (1931–2007) did much to reconcile Continental 

and analytic Philosophy. He argued that Dewey, Heidegger, and Ludwig Wittgenstein were the 

three greatest philosophers of the 20th century specifically because of their attacks on the 

Epistemological tradition of modern Philosophy.258 

 

12.6 Later Analytic Epistemology 

 

Beginning in the last quarter of the twentieth century, important contributions to Epistemology 

were made by researchers in neuroscience, psychology, artificial intelligence, and computer 

science. Those investigations produced insights into the nature of vision, the formation of mental 

representations of the external world, and the storage and retrieval of information in memory, 

among many other processes.259 In effect, the new approaches, revived theories of indirect 

perception that emphasized the subjective experience of the observer. Indeed, many such theories 

made use of concepts—such as “qualia” and “felt sensation”—that were essentially equivalent to 

the notion of sense-data.260 

 

Some of the new approaches also seemed to lend support to skeptical conclusions of the sort that 

early sense-data theorists had attempted to overcome. The neurologist Richard Gregory (1923–

2010), for example, argued in 1993 that: 

 

 No theory of direct perception, such as that proposed by 

Gibson, could be supported, given the indirectness imposed 

by the many physiological steps or stages of visual and 

other sensory perception.…For these and other reasons we 

may safely abandon direct accounts of perception in favor 

                                                             
256 https:www.britannica.com/biography/jaques-derrida/ 
257 https:www.britannica.com/biography/john-dewey/ 
258 https:www.britannica.com/biography/Richard-rorty/ 
259 F. Barone,Logical Empericism: Historical and Contemporary Perspectives (Pittsburgh: University of Pittsburgh 
Press, 2003), 57. 
260 Ibid. 

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of indirectly related and never certain…hypotheses of 

reality.261 

Similarly,  the work of Vilayanur Ramachandran, a neurologist, (born 1951), showed that the 

stimulation of certain areas of the brain in normal people produces sensations comparable to 

those felt in so-called “phantom limb” phenomena (the experience by an amputee of pains or 

other sensations that seem to be located in a missing limb). The conclusion that Ramachandran 

drew from his work is a modern variation of Descartes’s “evil genius” hypothesis: that we can 

never be certain that the sensations we experience accurately reflect an external reality.262 

On the basis of such experimental findings, many Philosophers adopted forms of 

radical skepticism. Benson Mates (1919–2009), for example, declared: 

Ultimately the only basis I can have for a claim to know 

that there exists something other than my own perceptions 

is the nature of those very perceptions, but they could be 

just as they are even if there did not exist anything else. 

Ergo, I have no basis for the knowledge-claim in 

question.263 

Mates concluded, that human beings cannot make any justifiable assertions about anything other 

than their own sense experiences. 

Philosophers have responded to such challenges in a variety of ways. Avrum Stroll (1921–2013), 

for example, argued that the views of skeptics such as Mates, as well those of many other 

modern proponents of indirect perception, rest on a conceptual mistake: the failure to distinguish 

between scientific and Philosophical accounts of the connection between sense experience and 

objects in the external world.264 In the case of vision, the scientific account (or, as he called it, 

the “causal story”) describes the familiar sequence of events that occurs according to well-known 

optical and physical laws. Citing that account, proponents of indirect perception point out that 

every event in such a causal sequence results in some modification of the input it receives from 

the preceding event. Thus, the light energy that strikes the retina is converted to electrochemical 

energy by the rods and cones, among other nerve cells, and the electrical impulses transmitted 

along the nervous pathways leading to the brain are reorganized in important ways at every 

synapse.265 From the fact that the input to every event in the sequence undergoes some 

modification, it follows that the end result of the process, the visual representation of the external 

object, must differ considerably from the elements of the original input, including the object 

                                                             
261 Ibid. 
262 Ibid.,58. 
263 https://www.britannica.com/biography/benson-mates/ 
264 F. Barone,Logical Empericism, 63. 
265 Ibid. 

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itself. From that observation, theorists of indirect perception who are inclined 

toward skepticism conclude that one cannot be certain that the sensation one experiences in 

seeing a particular object represents the object as it really is.266 

But the last inference is unwarranted, according to Stroll Avrum. What the argument shows is 

only that the visual representation of the object and the object itself are different (a fact that 

hardly needs pointing out). It does not show that one cannot be certain whether the representation 

is accurate.267 Indeed, a strong argument can be made to show that human perceptual experiences 

cannot all be inaccurate, or “modified,” in this way, for if they were, then it would be impossible 

to compare any given perception with its object in order to determine whether the sensation 

represented the object accurately, but in that case it also would be impossible to verify the claim 

that all our perceptions are inaccurate. Hence, the claim that all our perceptions are inaccurate is 

scientifically un-testable. According to Stroll, that is a decisive objection against the skeptical 

position. 

The implications of such developments in the cognitive sciences are clearly important for 

epistemology. The experimental evidence adduced for indirect perception has raised 

philosophical discussion of the nature of human perception to a new level. It is clear that a 

serious debate has begun, and at this point it is impossible to predict its outcome. 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                             
266 Ibid. 
267 Ibid, 64-65. 

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CHAPTER THIRTEEN 

SOME SCHOOL OF THOUGHTS IN EPISTEMOLOGY 

13.1 Empiricism 

In Philosophy, empiricism is a theory that states that knowledge comes only or primarily 

from sensory experience.268 Empiricism emphasizes the role of empirical evidence in the 

formation of ideas, rather than innate ideas or traditions.269However, Empiricists may argue that 

traditions (or customs) arise due to relations of previous sense experiences.270 Historically, 

empiricism was associated with the “blank slate” concept (tabula rasa), according to which the 

human mind is blank at birth and develops its thoughts only through experience. 

Empiricism in the Philosophy of science emphasizes evidence, especially as discovered 

in experiments. It is a fundamental part of the scientific method that all hypotheses and theories 

must be tested against observations of the natural world rather than resting solely on a 

priori reasoning, intuition, or revelation. Empiricism, often used by natural scientists, says that 

knowledge is acquired from experience and that knowledge is tentative and probabilistic, subject 

to continued revision and falsification.271 Empirical research, including experiments and 

validated measurement tools, guides the scientific method. 

13.2 Rationalism 

Rationalism is the view that regards reason as the main source and test of knowledge. Holding 

that reality itself has an inherently logical structure, the rationalist asserts that a class 

of truths exists and that the intellect can grasp directly. According to the rationalists, there are 

certain rational principles—especially in logic and mathematics, including 

in ethics and metaphysics, there are so fundamental that to deny them is to fall into contradiction. 

The rationalists’ confidence in reason and proof tends, therefore, to detract from their respect for 

other ways of knowing. 

Rationalism is any view appealing to intellectual and deductive reason (as opposed to sensory 

experience or any religious teachings) as the source of knowledge or justification. Thus, it holds 

that some propositions are knowable either through intuition or through being deduced through 

valid arguments from intuited propositions. Depending on the strength of the belief, this can result 

in a range of positions from the moderate view that reason has precedence over other ways of 

acquiring knowledge, to the radical position that reason is the only path to knowledge. 

13.3 Skepticism 

                                                             
268 H.C. Ezebuilo, “Locke, Berkeley and Hume: A Brief Survey of Empiricism,” International Journal of Research in 
Education, Humanities and Commerce 1(2), (2020), 84. 
269 Ibid. 
270 Ibid. 
271 Cf. H.C. Ezebuilo and I.N. Okechukwu, “A Hermeneutic Consideration of Karl Popper’s Falsification Theory,” 
Nnamdi Azikiwe Journal of Philosophy, 12(2), (2021). 

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Skepticism is a position that questions the possibility of human knowledge, either in particular 

domains or on a general level. Skepticism does not refer to any one specific school of 

philosophy, but is rather a thread that runs through many Epistemological debates. Ancient 

Greek skepticism began during the Hellenistic period in philosophy, which featured 

both Pyrrhonism (notably defended by Pyrrho and Sextus Empiricus) and Academic 

skepticism (notably defended by Arcesilaus and Carneades). Among ancient Indian 

Philosophers, skepticism was notably defended by the Ajñana school and in the 

Buddhist Madhyamika tradition. In modern Philosophy, René Descartes' famous inquiry into 

mind and body began as an exercise in skepticism, in which he started by trying to doubt all 

purported cases of knowledge in order to search for something that was known with 

absolute certainty. 

12.4 Pragmatism 

Pragmatism is an Empiricist Epistemology formulated by Charles Sanders Peirce, William 

James, and John Dewey, which understands truth as that which is practically applicable in the 

world. Pragmatists often treat truth as the final outcome of ideal scientific inquiry, meaning that 

something cannot be true unless it is potentially observable. Peirce formulates the maxim: 

“Consider what effects, that might conceivably have practical bearings, we conceive the object 

of our conception to have. Then, our conception of these effects is the whole of our conception 

of the object.”272 This suggests that we are to analyse ideas and objects in the world for their 

practical value. This is in contrast to any correspondence theory of truth that holds that what is 

true is what corresponds to an external reality. William James suggests that through a pragmatist 

epistemology, theories “become instruments, not answers to enigmas in which we can rest.”273 

In the late 19th and early 20th century, several forms of pragmatic Philosophy arose. The ideas 

of pragmatism, in its various forms, developed mainly from discussions between Charles Sanders 

Peirce and William James as already noted. James popularized the term “pragmatism,” giving 

Peirce full credit for its patrimony, but Peirce later demurred from the tangents that the 

movement was taking, and redubbed what he regarded as the original idea with the name of 

“pragmaticism.” Along with its pragmatic theory of truth, this perspective integrates the basic 

insights of empirical (experience-based) and rational (concept-based) thinking. 

13.4.1 Charles Peirce 

Charles Peirce (1839–1914) was highly influential in laying the groundwork for today’s 

empirical scientific method. Although Peirce severely criticized many elements of Descartes’ 

peculiar brand of rationalism, he did not reject rationalism outright. Indeed, he concurred with 

the main ideas of rationalism, most importantly the idea that rational concepts can be meaningful 

and the idea that rational concepts necessarily go beyond the data given by empirical 

observation. In later years he even emphasized the concept-driven side of the then ongoing 

                                                             
272 W. James, and G. Gunn, Pragmatism and other Essays, 32-33. 
273 Ibid. 

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debate between strict empiricism and strict rationalism, in part to counterbalance the excesses to 

which some of his cohorts had taken pragmatism under the “data-driven” strict-empiricist view. 

Among Peirce’s major contributions was to place inductive reasoning and deductive reasoning in 

a complementary rather than competitive mode, the latter of which had been the primary trend 

among the educated since David Hume wrote a century before. To this, Peirce added the concept 

of abductive reasoning. The combined three forms of reasoning serve as a primary conceptual 

foundation for the empirically based scientific method today. Peirce’s approach presupposes that 

(1) the objects of knowledge are real things, (2) the characters (properties) of real things do not 

depend on our perceptions of them, and (3) everyone who has sufficient experience of real things 

will agree on the truth about them. According to Peirce’s doctrine of fallibilism, the conclusions 

of science are always tentative. The rationality of the scientific method does not depend on the 

certainty of its conclusions, but on its self-corrective character: by continued application of the 

method, science can detect and correct its own mistakes, and thus eventually lead to the 

discovery of truth.274 

In his Harvard “Lectures on Pragmatism” (1903), Peirce enumerated what he called the “three 

cotary propositions of pragmatism” (cotis, whetstone), saying that they “put the edge on 

the maxim of pragmatism.” First among these, he listed the peripatetic-thomist observation 

mentioned above, but he further observed that this link between sensory perception and 

intellectual conception is a two-way street. That is, it can be taken to say that whatever we find in 

the intellect is also incipiently in the senses. Hence, if theories are theory-laden then so are the 

senses, and perception itself can be seen as a species of abductive inference, its difference being 

that it is beyond control and hence beyond critique—in a word, incorrigible. This in no way 

conflicts with the fallibility and revisability of scientific concepts, since it is only the immediate 

percept in its unique individuality or “thisness”—what the Scholastics called its haecceity—that 

stands beyond control and correction. Scientific concepts, on the other hand, are general in 

nature, and transient sensations do in another sense find correction within them. This notion of 

perception as abduction has received periodic revivals in artificial intelligence and cognitive 

science research, most recently for instance with the work of Irvin Rock on indirect 

perception.275 

13.4.2 William James 

Around the beginning of the 20th century, William James (1842–1910) coined the term “radical 

empiricism” to describe an offshoot of his form of pragmatism, which he argued could be dealt 

with separately from his pragmatism—though in fact the two concepts are intertwined in James’s 

published lectures. James maintained that the empirically observed “directly apprehended 

universe needs…no extraneous trans-empirical connective support,”276 by which he meant to rule 

out the perception that there can be any value added by seeking supernatural explanations 

                                                             
274 “Empiricism,” Macmillan Encyclopedia of Philosophy,551. 
275 Irvin Rock, Indirect Perception (Cambridge, Massachusetts, 1997), 77-78. 
276 William James, the Meaning of Truth (1911), https://www.communicationcache.com. 

https://en.wikipedia.org/wiki/Inductive_reasoning
https://en.wikipedia.org/wiki/Deductive_reasoning
https://en.wikipedia.org/wiki/Abductive_reasoning
https://en.wikipedia.org/wiki/Fallibilism
https://en.wikipedia.org/wiki/Pragmatic_maxim
https://en.wikipedia.org/wiki/Abductive_reasoning
https://en.wikipedia.org/wiki/Scholastics
https://en.wikipedia.org/wiki/Haecceity
https://en.wikipedia.org/wiki/Artificial_intelligence
https://en.wikipedia.org/wiki/Cognitive_science
https://en.wikipedia.org/wiki/Cognitive_science
https://en.wikipedia.org/wiki/Irvin_Rock
https://en.wikipedia.org/wiki/Indirect_perception
https://en.wikipedia.org/wiki/Indirect_perception
https://en.wikipedia.org/wiki/Radical_empiricism
https://en.wikipedia.org/wiki/Radical_empiricism
https://en.wikipedia.org/wiki/Value_added
https://en.wikipedia.org/wiki/Supernatural


117 
 

for natural phenomena. James’ “radical empiricism” is thus not radical in the context of the term 

empiricism, but is instead fairly consistent with the modern use of the term empirical. 

John Dewey (1859–1952) modified James’ pragmatism to form a theory known 

as instrumentalism. The role of sense experience in Dewey’s theory is crucial, in that he saw 

experience as unified totality of things through which everything else is interrelated. Dewey’s 

basic thought, in accordance with empiricism, was that reality is determined by past experience. 

Therefore, humans adapt their past experiences of things to perform experiments upon and test 

the pragmatic values of such experience. The value of such experience is measured experientially 

and scientifically, and the results of such tests generate ideas that serve as instruments for future 

experimentation, in physical sciences as in ethics.277 Thus, ideas in Dewey’s system retain their 

empiricist flavour in that they are only known a posteriori. 

Contemporary versions of pragmatism have been most notably developed by Richard 

Rorty and Hilary Putnam. Rorty proposed that values were historically contingent and dependent 

upon their utility within a given historical period.278  Contemporary philosophers working in 

pragmatism are called neopragmatists, and also include Nicholas Rescher, Robert 

Brandom, Susan Haack, and Cornel West. 

13.5 Naturalized Epistemology 

In certain respects an intellectual descendant of pragmatism, naturalized epistemology considers 

the evolutionary role of knowledge for agents living and evolving in the world.279 It de-

emphasizes the questions around justification and truth, and instead asks, empirically, how 

reliable beliefs are formed and the role that evolution played in the development of such 

processes. It suggests a more empirical approach to the subject as a whole, leaving behind 

philosophical definitions and consistency arguments, and instead using psychological methods to 

study and understand how knowledge is actually formed and is used in the natural world. As 

such, it does not attempt to answer the analytic questions of traditional epistemology, but rather 

replace them with new empirical ones.280 

Naturalized epistemology was first proposed in “Epistemology Naturalized”, a seminal paper 

by W.V.O. Quine.281 A less radical view has been defended by Hilary Kornblith in Knowledge 

and its Place in Nature, in which he seeks to turn epistemology towards empirical investigation 

without completely abandoning traditional epistemic concepts. 

13.6 Feminist Epistemology 

                                                             
277Eric Thomas Weber, “What Experimentalism Means in Ethics,” The Journal of Speculative Philosophy, no. 25 
(2011), 99. 
278 R. Rorty, Consequences of Pragmatism (Minneapolis: University of Minnesota Press, 1982). 
279Kim Jaegwon, “What Is Naturalized Epistemology?” Philosophical Perspectives, 2, (1988), 405. 
280 Ibid. 
281 Wilard V.O. Quine, “Epistemology Naturalized.” In E. Sosa & J. Kim (eds.). Epistemology: An Anthology (Malden, 
MA: Blackwell Publishing, 2004), 292. 

https://en.wikipedia.org/wiki/Nature
https://en.wikipedia.org/wiki/Phenomena
https://en.wikipedia.org/wiki/Empirical
https://en.wikipedia.org/wiki/John_Dewey
https://en.wikipedia.org/wiki/Instrumentalism
https://en.wikipedia.org/wiki/Reality
https://en.wikipedia.org/wiki/Methodological_pragmatism
https://en.wikipedia.org/wiki/Richard_Rorty
https://en.wikipedia.org/wiki/Richard_Rorty
https://en.wikipedia.org/wiki/Hilary_Putnam
https://en.wikipedia.org/wiki/Neopragmatism
https://en.wikipedia.org/wiki/Nicholas_Rescher
https://en.wikipedia.org/wiki/Robert_Brandom
https://en.wikipedia.org/wiki/Robert_Brandom
https://en.wikipedia.org/wiki/Susan_Haack
https://en.wikipedia.org/wiki/Cornel_West
https://en.wikipedia.org/wiki/Naturalized_epistemology
https://en.wikipedia.org/wiki/W.V.O._Quine
https://en.wikipedia.org/wiki/Hilary_Kornblith
https://en.wikipedia.org/wiki/Blackwell_Publishing


118 
 

Feminist epistemology is a subfield of epistemology which applies feminist theory to 

epistemological questions. It began to emerge as a distinct subfield in the 20th century. 

Prominent feminist epistemologists include Miranda Fricker (who developed the concept 

of epistemic injustice), Donna Haraway (who first proposed the concept of situated 

knowledge), Sandra Harding, and Elizabeth Anderson.282 Harding proposes that feminist 

epistemology can be broken into three distinct categories: Feminist empiricism, standpoint 

epistemology, and postmodern epistemology.283 Feminist epistemology has also played a 

significant role in the development of many debates in social epistemology. 

13.7 Relativism 

Epistemic relativism is the view that what is true, rational, or justified for one person need not be 

true, rational, or justified for another person. Epistemic relativists therefore assert that while 

there are relative facts about truth, rationality, justification, and so on, there is no perspective-

independent fact of the matter.284[78] Note that this is distinct from epistemic contextualism, 

which holds that the meaning of epistemic terms vary across contexts (e.g. “I know” might mean 

something different in everyday contexts and skeptical contexts). In contrast, epistemic 

relativism holds that the relevant facts vary, not just linguistic meaning. Relativism about truth 

may also be a form of ontological relativism, insofar as relativists about truth hold that facts 

about what exists vary based on perspective. 

 

13.8 Constructivism 

Constructivism is a view in philosophy according to which all knowledge is a compilation of 

human-made constructions, not the neutral discovery of an objective truth. Whereas objectivism 

is concerned with the object of our knowledge, constructivism emphasizes how we construct 

knowledge.285 Constructivism proposes new definitions for knowledge and truth, which 

emphasize intersubjectivity rather than objectivity, and viability rather than truth. The 

constructivist point of view is in many ways comparable to certain forms of pragmatism. 

13.9 Idealism 

Idealism is a broad term referring to both an ontological view about the world being in some 

sense mind-dependent and a corresponding epistemological view that everything we know can 

be reduced to mental phenomena. First and foremost, idealism is a metaphysical doctrine. As an 

epistemological doctrine, idealism shares a great deal with both empiricism and rationalism. 

Some of the most famous empiricists have been classified as idealists (particularly Berkeley), 

and yet the subjectivism inherent to idealism also resembles that of Descartes in many respects. 

Many idealists believe that knowledge is primarily (at least in some areas) acquired by a 

                                                             
282“Feminist Epistemology,” Stanford Encyclopedia of Philosophy. Retrieved October 31, 2021. 
283 Ibid. 
284 
285 Alan Hájek and Hanti Lin, “A Tale of Two Epistemologies?” Res Philosophica, 94 (2), (2017), 207. 

https://en.wikipedia.org/wiki/Feminist_epistemology
https://en.wikipedia.org/wiki/Feminist_theory
https://en.wikipedia.org/wiki/Miranda_Fricker
https://en.wikipedia.org/wiki/Epistemic_injustice
https://en.wikipedia.org/wiki/Donna_Haraway
https://en.wikipedia.org/wiki/Situated_knowledge
https://en.wikipedia.org/wiki/Situated_knowledge
https://en.wikipedia.org/wiki/Sandra_Harding
https://en.wikipedia.org/wiki/Elizabeth_S._Anderson
https://en.wikipedia.org/wiki/Social_epistemology
https://en.wikipedia.org/wiki/Epistemology#cite_note-Boghossian-82
https://en.wikipedia.org/wiki/Contextualism
https://en.wikipedia.org/wiki/Ontological
https://en.wikipedia.org/wiki/Social_constructivism
https://en.wikipedia.org/wiki/Knowledge
https://en.wikipedia.org/wiki/Truth
https://en.wikipedia.org/wiki/Idealism
https://en.wikipedia.org/wiki/Ontological
https://en.wikipedia.org/wiki/Metaphysical
https://en.wikipedia.org/wiki/George_Berkeley
https://en.wikipedia.org/wiki/Subjectivism
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
http://plato.stanford.edu/entries/feminism-epistemology/
https://philpapers.org/rec/HJEATO


119 
 

priori processes, or that it is innate—for example, in the form of concepts not derived from 

experience. The relevant theoretical concepts may purportedly be part of the structure of the 

human mind (as in Kant’s theory of transcendental idealism), or they may be said to exist 

independently of the mind (as in Plato's theory of Forms). 

Some of the most famous forms of idealism include transcendental idealism (developed 

by Immanuel Kant), subjective idealism (developed by George Berkeley), and absolute 

idealism (developed by Georg Wilhelm Friedrich Hegel and Friedrich Schelling). 

13.10 Bayesian Epistemology 

Bayesian epistemology is a formal approach to various topics in epistemology that has its roots 

in Thomas Bayes’ work in the field of probability theory. One advantage of its formal method in 

contrast to traditional epistemology is that its concepts and theorems can be defined with a high 

degree of precision. It is based on the idea that beliefs can be interpreted as subjective 

probabilities. As such, they are subject to the laws of probability theory, which act as the norms 

of rationality. These norms can be divided into static constraints, governing the rationality of 

beliefs at any moment, and dynamic constraints, governing how rational agents should change 

their beliefs upon receiving new evidence.286 The most characteristic Bayesian expression of 

these principles is found in the form of Dutch books, which illustrate irrationality in agents 

through a series of bets that lead to a loss for the agent no matter which of the probabilistic 

events occurs. Bayesians have applied these fundamental principles to various epistemological 

topics but Bayesianism does not cover all topics of traditional epistemology.287 

13.11 Indian Pramana 

Indian schools of philosophy, such as the Hindu Nyaya and Carvaka schools, and 

the Jain and Buddhist philosophical schools, developed an epistemological tradition 

independently of the Western philosophical tradition called pramana. Pramana can be translated 

as instrument of knowledge and refers to various means or sources of knowledge that Indian 

philosophers held to be reliable. Each school of Indian philosophy had their own theories about 

which pramanas were valid means to knowledge and which were unreliable (and 

why).288 A Vedic text, Taittirīya Āraṇyaka (c. 9th–6th centuries BCE), lists four means of 

attaining correct knowledge: smṛti (tradition or 

scripture), pratyakṣa (perception), aitihya (communication by one who is expert, or tradition), 

and anumāna (reasoning or inference).289 

In the Indian traditions, the most widely discussed pramanas 

are: Pratyakṣa (perception), Anumāṇa (inference), Upamāṇa (comparison and 

                                                             
286 Stephan Hartmann and Jan Sprenger, “Bayesian Epistemology.” The Routledge Companion to Epistemology 
(London: Routledge, 2010), 609. 
287 Ibid. 
288B.K. Matilal, Perception: An Essay on Classical Indian Theories of Knowledge” (Oxford University Press, 1986), xiv. 
289 Ibid. see also Jose I. Cabezón, “Truth in Buddhist Theology,” in R. Jackson and J. Makransky, (eds.), Buddhist 
Theology, Critical Reflections by Contemporary Buddhist Scholars (London: Curzon, 2000), 139. 

https://en.wikipedia.org/wiki/Innatism
https://en.wikipedia.org/wiki/Mind
https://en.wikipedia.org/wiki/Immanuel_Kant
https://en.wikipedia.org/wiki/Transcendental_idealism
https://en.wikipedia.org/wiki/Theory_of_Forms
https://en.wikipedia.org/wiki/Transcendental_idealism
https://en.wikipedia.org/wiki/Immanuel_Kant
https://en.wikipedia.org/wiki/Subjective_idealism
https://en.wikipedia.org/wiki/George_Berkeley
https://en.wikipedia.org/wiki/Absolute_idealism
https://en.wikipedia.org/wiki/Absolute_idealism
https://en.wikipedia.org/wiki/Georg_Wilhelm_Friedrich_Hegel
https://en.wikipedia.org/wiki/Friedrich_Wilhelm_Joseph_Schelling
https://en.wikipedia.org/wiki/Bayesian_epistemology
https://en.wikipedia.org/wiki/Thomas_Bayes
https://en.wikipedia.org/wiki/Subjective_probability
https://en.wikipedia.org/wiki/Subjective_probability
https://en.wikipedia.org/wiki/Probability_theory
https://en.wikipedia.org/wiki/Rationality
https://en.wikipedia.org/wiki/Dutch_book
https://en.wikipedia.org/wiki/Indian_philosophy
https://en.wikipedia.org/wiki/Hindu_philosophy
https://en.wikipedia.org/wiki/Nyaya
https://en.wikipedia.org/wiki/Carvaka
https://en.wikipedia.org/wiki/Jain_philosophy
https://en.wikipedia.org/wiki/Buddhist_philosophy
https://en.wikipedia.org/wiki/Vedas
https://en.wikipedia.org/wiki/Taittiriya_Aranyaka
https://philpapers.org/rec/BOVSIO


120 
 

analogy), Arthāpatti (postulation, derivation from circumstances), Anupalabdi (non-perception, 

negative/cognitive proof) and Śabda (word, testimony of past or present reliable experts). While 

the Nyaya school (beginning with the Nyāya Sūtras of Gotama, between 6th-century BCE and 

2nd-century BC290) were a proponent of realism and supported four pramanas (perception, 

inference, comparison/analogy and testimony), the Buddhist epistemologists 

(Dignaga and Dharmakirti) generally accepted only perception and inference. 

The Carvaka school of materialists only accepted the pramana of perception, and hence were 

among the first empiricists in the Indian traditions.291 Another school, the Ajñana, included 

notable proponents of philosophical skepticism. 

The theory of knowledge of the Buddha in the early Buddhist texts has been interpreted as a 

form of pragmatism as well as a form of correspondence theory.292 Likewise, the Buddhist 

philosopher Dharmakirti has been interpreted both as holding a form of pragmatism or 

correspondence theory for his view that what is true is what has effective power 

(arthakriya).293 The Buddhist Madhyamika school’s theory of emptiness (shunyata) meanwhile 

has been interpreted as a form of philosophical skepticism.294 

The main contribution to epistemology by the Jains has been their theory of “many sided-ness” 

or multi-perspectivism (Anekantavada), which says that since the world is multifaceted, any 

single viewpoint is limited (naya – a partial standpoint).295 This has been interpreted as a kind of 

pluralism or perspectivism. According to Jain epistemology, none of the pramanas gives absolute 

or perfect knowledge since they are each limited points of view. 

13.12 Social Epistemology 

Social epistemology deals with questions about knowledge in contexts where our knowledge 

attributions cannot be explained by simply examining individuals in isolation from one another, 

meaning that the scope of our knowledge attributions must be widened to include broader social 

contexts. It also explores the ways in which interpersonal beliefs can be justified in social 

contexts. The most common topics discussed in contemporary social epistemology 

are testimony, which deals with the conditions under which a belief “x is true” which resulted 

from being told “x is true” constitutes knowledge; peer disagreement, which deals with when and 

how I should revise my beliefs in light of other people holding beliefs that contradict mine; and 

group epistemology, which deals with what it means to attribute knowledge to groups rather than 

individuals, and when group knowledge attributions are appropriate. 

13.13 Formal Epistemology 

                                                             
290 Ibid. 
291 Ibid. 
292D. Long, Jainism: An Introduction, 125. 
293 Ibid. 
294 Ibid. 
295 Ibid. 

https://en.wikipedia.org/wiki/Ny%C4%81ya_S%C5%ABtras
https://en.wikipedia.org/wiki/Dignaga
https://en.wikipedia.org/wiki/Dharmakirti
https://en.wikipedia.org/wiki/Carvaka
https://en.wikipedia.org/wiki/Materialists
https://en.wikipedia.org/wiki/Empiricists
https://en.wikipedia.org/wiki/Aj%C3%B1ana
https://en.wikipedia.org/wiki/Philosophical_skepticism
https://en.wikipedia.org/wiki/Buddhist_philosophy#Epistemology
https://en.wikipedia.org/wiki/Dharmakirti
https://en.wikipedia.org/wiki/Madhyamika
https://en.wikipedia.org/wiki/Shunyata
https://en.wikipedia.org/wiki/Philosophical_skepticism
https://en.wikipedia.org/wiki/Anekantavada
https://en.wikipedia.org/wiki/Perspectivism
https://en.wikipedia.org/wiki/Jain_epistemology
https://en.wikipedia.org/wiki/Testimony


121 
 

Formal epistemology uses formal tools and methods from decision theory, logic, probability 

theory and computability theory to model and reason about issues of epistemological 

interest.[102] Work in this area spans several academic fields, including philosophy, computer 

science, economics, and statistics. The focus of formal epistemology has tended to differ 

somewhat from that of traditional epistemology, with topics like uncertainty, induction, and 

belief revision garnering more attention than the analysis of knowledge, skepticism, and issues 

with justification. 

13.14 Metaepistemology 

Metaepistemology is the metaphilosophical study of the methods, aims, and subject matter of 

epistemology.[103] In general, metaepistemology aims to better understand our first-order 

epistemological inquiry. Some goals of metaepistemology are identifying inaccurate assumptions 

made in epistemological debates and determining whether the questions asked in mainline 

epistemology are the right epistemological questions to be asking. 

13.15 Realism 

Epistemological realism is a philosophical position holding that what can be known about an 

object exists independently of one’s mind.296 It is opposed to epistemological idealism. Reality 

as a school of thought believes that it is possible to obtain knowledge about mind-independent 

reality. It is the viewpoint which accords to things which are known or perceived as existence or 

nature which is independent of whether anyone is thinking about or perceiving them. While there 

are certainly significant similarities linking the variety of positions commonly described as 

realist, there are also important differences which obstruct any straightforward general 

characterization of realism. 

 

 

 

 

 

 

 

 

 

                                                             
296 John Haldane, Crispin Wright (eds.), Reality, Representation, and Projection, (Oxford: oxford University Press, 
1993), 16. 

https://en.wikipedia.org/wiki/Decision_theory
https://en.wikipedia.org/wiki/Logic
https://en.wikipedia.org/wiki/Probability_theory
https://en.wikipedia.org/wiki/Probability_theory
https://en.wikipedia.org/wiki/Computability_theory
https://en.wikipedia.org/wiki/Epistemology#cite_note-SEP_Formal-106
https://en.wikipedia.org/wiki/Philosophy
https://en.wikipedia.org/wiki/Computer_science
https://en.wikipedia.org/wiki/Computer_science
https://en.wikipedia.org/wiki/Economics
https://en.wikipedia.org/wiki/Statistics
https://en.wikipedia.org/wiki/Metaphilosophical
https://en.wikipedia.org/wiki/Philosophical_method
https://en.wikipedia.org/wiki/Epistemology#cite_note-107


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CHAPTER FOURTEEN 

EMPIRICISM 

14.1 What is Empiricism? 

Empiricism is the view that all concepts originate in experience, that all concepts are about or 

applicable to things that can be experienced, or that all rationally acceptable beliefs or 

propositions are justifiable or knowable only through experience. This broad definition accords 

with the derivation of the term empiricism from the ancient Greek word empeiria, “experience.” 

Concepts are said to be “a posteriori” (Latin: “from the latter”) if they can be applied only on the 

basis of experience, and they are called “a priori” (“from the former”) if they can be applied 

independently of experience. Beliefs or propositions are said to be a posteriori if they are 

knowable only on the basis of experience and a priori if they are knowable independently of 

experience. Thus, according to the second and third definitions of empiricism above, empiricism 

is the view that all concepts, or all rationally acceptable beliefs or propositions, are a posteriori 

rather than a priori. 

The first two definitions of empiricism typically involve an implicit theory of meaning, 

according to which words are meaningful only insofar as they convey concepts. Some 

empiricists have held that all concepts are either mental “copies” of items that are directly 

experienced or complex combinations of concepts that are themselves copies of items that are 

directly experienced. This view is closely linked to the notion that the conditions of application 

of a concept must always be specified in experiential terms. 

The third definition of empiricism is a theory of knowledge, or theory of justification. It views 

beliefs, or at least some vital classes of belief—e.g., the belief that this object is red—as 

depending ultimately and necessarily on experience for their justification. An equivalent way of 

stating this thesis is to say that all human knowledge is derived from experience. 

Empiricism regarding concepts and empiricism regarding knowledge do not strictly imply each 

other. Many empiricists have admitted that there are a priori propositions but have denied that 

there are a priori concepts. It is rare, however, to find a philosopher who accepts a priori 

concepts but denies a priori propositions. 

Stressing experience, empiricism often opposes the claims of authority, intuition, imaginative 

conjecture, and abstract, theoretical, or systematic reasoning as sources of reliable belief. Its 

most fundamental antithesis is with the latter—i.e., with rationalism, also called intellectualism 

or apriorism. A rationalist theory of concepts asserts that some concepts are a priori and that 

these concepts are innate, or part of the original structure or constitution of the mind. A 

rationalist theory of knowledge, on the other hand, holds that some rationally acceptable 

https://www.britannica.com/topic/definition
https://www.britannica.com/topic/belief
https://www.merriam-webster.com/dictionary/implicit
https://www.britannica.com/topic/meaning
https://www.britannica.com/topic/epistemology
https://www.britannica.com/topic/belief
https://www.britannica.com/topic/a-priori-knowledge
https://www.merriam-webster.com/dictionary/intuition
https://www.merriam-webster.com/dictionary/antithesis
https://www.britannica.com/topic/rationalism
https://www.britannica.com/topic/innate-idea
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propositions—perhaps including “everything must have a sufficient reason for its existence” 

(the principle of sufficient reason)—are a priori. A priori propositions, according to rationalists, 

can arise from intellectual intuition, from the direct apprehension of self-evident truths, or from 

purely deductive reasoning. 

 

Empiricism is a view in the theory of knowledge which focuses on the role of experience, 

especially experience based on perceptual observations by the senses, in the generation of 

knowledge. Certain forms exempt disciplines such as mathematics and logic from these 

requirements. 

There are many variants of empiricism, including British empiricism, logical 

empiricism, phenomenalism, and some versions of common sense philosophy. Most forms of 

empiricism give epistemologically privileged status to sensory impressions or sense data, 

although this plays out very differently in different cases. Some of the most famous historical 

empiricists include John Locke, David Hume, George Berkeley, Francis Bacon, John Stuart 

Mill, Rudolf Carnap, and Bertrand Russell. 

In philosophy, empiricism is a theory that states that knowledge comes only or primarily 

from sensory experience.297 Empiricism emphasizes the role of empirical evidence in the 

formation of ideas, rather than innate ideas or traditions.298However, empiricists may argue that 

traditions (or customs) arise due to relations of previous sense experiences.299 Historically, 

empiricism was associated with the “blank slate” concept (tabula rasa), according to which the 

human mind is blank at birth and develops its thoughts only through experience. 

Empiricism in the philosophy of science emphasizes evidence, especially as discovered 

in experiments. It is a fundamental part of the scientific method that all hypotheses and theories 

must be tested against observations of the natural world rather than resting solely on a 

priori reasoning, intuition, or revelation. Empiricism, often used by natural scientists, says that 

knowledge is based on experience and that knowledge is tentative and probabilistic, subject to 

continued revision and falsification.300 Empirical research, including experiments and validated 

measurement tools, guides the scientific method. 

 

 

 

 

                                                             
297 H.C. Ezebuilo, “Locke, Berkeley and Hume: A Brief Survey of Empiricism,” International Journal of Research in 
Education, Humanities and Commerce 1(2), (2020), 84. 
298 Ibid. 
299 Ibid. 
300 Cf. H.C. Ezebuilo and I.N. Okechukwu, “A Hermeneutic Consideration of Karl Popper’s Falsification Theory,” 
Nnamdi Azikiwe Journal of Philosophy, 12(2), (2021). 

https://www.britannica.com/topic/principle-of-sufficient-reason
https://www.merriam-webster.com/dictionary/intellectual
https://www.britannica.com/topic/perception
https://www.britannica.com/topic/deduction-reason
https://en.wikipedia.org/wiki/Empiricism
https://en.wikipedia.org/wiki/Perception
https://en.wikipedia.org/wiki/Sense
https://en.wikipedia.org/wiki/Mathematics
https://en.wikipedia.org/wiki/Logic
https://en.wikipedia.org/wiki/British_empiricism
https://en.wikipedia.org/wiki/Empiricism#Logical_empiricism
https://en.wikipedia.org/wiki/Empiricism#Logical_empiricism
https://en.wikipedia.org/wiki/Phenomenalism
https://en.wikipedia.org/wiki/Scottish_common_sense_realism
https://en.wikipedia.org/wiki/Sense_data
https://en.wikipedia.org/wiki/John_Locke
https://en.wikipedia.org/wiki/David_Hume
https://en.wikipedia.org/wiki/George_Berkeley
https://en.wikipedia.org/wiki/Francis_Bacon
https://en.wikipedia.org/wiki/John_Stuart_Mill
https://en.wikipedia.org/wiki/John_Stuart_Mill
https://en.wikipedia.org/wiki/Rudolf_Carnap
https://en.wikipedia.org/wiki/Bertrand_Russell
https://en.wikipedia.org/wiki/Philosophy
https://en.wikipedia.org/wiki/Theory
https://en.wikipedia.org/wiki/Empirical_evidence
https://en.wikipedia.org/wiki/Empirical_evidence
https://en.wikipedia.org/wiki/Innate_idea
https://en.wikipedia.org/wiki/Traditions
https://en.wikipedia.org/wiki/Philosophy_of_science
https://en.wikipedia.org/wiki/Experiment
https://en.wikipedia.org/wiki/Scientific_method
https://en.wikipedia.org/wiki/A_priori_(philosophy)
https://en.wikipedia.org/wiki/A_priori_(philosophy)
https://en.wikipedia.org/wiki/Intuition_(knowledge)
https://en.wikipedia.org/wiki/Revelation
https://en.wikipedia.org/wiki/Falsifiability
https://en.wikipedia.org/wiki/Scientific_method


124 
 

14.2 Various Meanings of Empiricism 

 

14.2.1 Broader Senses 

 

In both everyday attitudes and philosophical theories, the experiences referred to by empiricists 

are principally those arising from the stimulation of the sense organs—i.e., from visual, 

auditory, tactile, olfactory, and gustatory sensation. (In addition to these five kinds of sensation, 

some empiricists also recognize kinesthetic sensation, or the sensation of movement.) Most 

philosophical empiricists, however, have maintained that sensation is not the only provider of 

experience, admitting as empirical the awareness of mental states in introspection or reflection 

(such as the awareness that one is in pain or that one is frightened); such mental states are then 

often described metaphorically as being present to  an “inner sense.” It is a controversial question 

whether still further types of experience, such as moral, aesthetic, or religious experience, ought 

to be acknowledged as empirical. A crucial consideration is that, as the scope of “experience” is 

broadened, it becomes increasingly difficult to distinguish a domain of genuinely a priori 

propositions. If, for example, one were to take the mathematician’s intuition of relationships 

between numbers as a kind of experience, one would be hard-pressed to identify any kind of 

knowledge that is not ultimately empirical. 

 

Even when empiricists agree on what should count as experience, however, they may still 

disagree fundamentally about how experience itself should be understood. Some empiricists, for 

example, conceive of sensation in such a way that what one is aware of in sensation is always a 

mind-dependent entity (sometimes referred to as a “sense datum”). Others embrace some version 

of “direct realism,” according to which one can directly perceive or be aware of physical objects 

or physical properties. Thus there may be radical theoretical differences even among empiricists 

who are committed to the notion that all concepts are constructed out of elements given in 

sensation. 

 

Two other viewpoints related to but not the same as empiricism are the pragmatism of the 

American philosopher and psychologist William James, an aspect of which was what he 

called radical empiricism, and logical positivism, sometimes also called logical empiricism. 

Although these philosophies are empirical in some sense, each has a distinctive focus that 

warrants its treatment as a separate movement. Pragmatism stresses the involvement of ideas in 

practical experience and action, whereas logical positivism is more concerned with the 

justification of scientific knowledge. 

 

When describing an everyday attitude, the word empiricism sometimes conveys an 

unfavourable implication of ignorance of or indifference to relevant theory. Thus, to call a doctor 

an “Empiric” has been to call him a quack—a usage traceable to a sect of medical men who were 

opposed to the elaborate medical—and in some views metaphysical—theories inherited from the 

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125 
 

Greek physician Galen of Pergamum (129–c. 216 CE). The medical empiricists opposed to 

Galen preferred to rely on treatments of observed clinical effectiveness, without inquiring into 

the mechanisms sought by therapeutic theory. But empiricism, detached from this medical 

association, may also be used, more favourably, to describe a hard-headed refusal to be swayed 

by anything but the facts that the thinker has observed for himself, a blunt resistance to received 

opinion or precarious chains of abstract reasoning. 

 

14.2.2 Stricter Senses 

 

As a more strictly defined movement, empiricism reflects certain fundamental distinctions and 

occurs in varying degrees. Empiricism, whether concerned with concepts or knowledge, can be 

held with varying degrees of strength. On this basis, absolute, substantive, and partial 

empiricisms can be distinguished. 

 

12.2.2.1 Absolute Empiricism 

Absolute empiricists hold that there are no a priori concepts, either formal or categorial, and no a 

priori beliefs or propositions. Absolute empiricism about the former is more common than that 

about the latter, however. Although nearly all Western philosophers admit that 

obvious tautologies (e.g., “all red things are red”) and definitional truisms (e.g., “all triangles 

have three sides”) are a priori, many of them would add that these represent a degenerate case. 

 

12.2.2.2 Substantive Empiricism 

 

A more moderate form of empiricism is that of the substantive empiricists, who are unconvinced 

by attempts that have been made to interpret formal concepts empirically and who therefore 

concede that formal concepts are a priori, though they deny that status to categorial concepts and 

to the theoretical concepts of physics, which they hold are a posteriori. According to this view, 

allegedly a priori categorial and theoretical concepts are either defective, reducible to empirical 

concepts, or merely useful “fictions” for the prediction and organization of experience. 

 

The parallel point of view about knowledge assumes that the truth of logical and mathematical 

propositions is determined, as is that of definitional truisms, by the relationships between 

meanings that are established prior to experience. The truth often espoused by ethicists, for 

example, that one is truly obliged to rescue a person from drowning only if it is possible to do so, 

is a matter of meanings and not of facts about the world. On this view, all propositions that, in 

contrast to the foregoing example, are in any way substantially informative about the world are a 

posteriori. Even if there are a priori propositions, they are formal or verbal or conceptual in 

nature, and their necessary truth derives simply from the meanings that attached to the words 

they contain. A priori knowledge is useful because it makes explicit the hidden implications of 

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126 
 

substantive, factual assertions. But a priori propositions do not themselves express genuinely 

new knowledge about the world; they are factually empty. Thus “All bachelors are unmarried” 

merely gives explicit recognition to the commitment to describe as unmarried anyone who has 

been described as a bachelor. 

 

Substantive empiricism about knowledge regards all a priori propositions as being more-or-less 

concealed tautologies. If a person’s “duty” is thus defined as that which he should always do, the 

statement “A person should always do his duty” then becomes “A person should always do what 

he should always do.” Deductive reasoning is conceived accordingly as a way of bringing this 

concealed tautological status to light. That such extrication is nearly always required means 

that a priori knowledge is far from trivial. 

For the substantive empiricist, truisms and the propositions of logic and mathematics exhaust the 

domain of the a priori. Science, on the other hand—from the fundamental assumptions about the 

structure of the universe to the singular items of evidence used to confirm its theories—is 

regarded as a posteriori throughout. The propositions of ethics and those of metaphysics, which 

deals with the ultimate nature and constitution of reality (e.g., “only that which is not subject to 

change is real”), are either disguised tautologies or “pseudo-propositions,” that is, combinations 

of words that, despite their grammatical respectability, cannot be taken as true or false assertions 

at all. 

 

14.2.2.3 Partial Empiricism 

 

The least thoroughgoing type of empiricism here distinguished, ranking third in degree, can be 

termed partial empiricism. According to this view, the realm of the a priori includes some 

concepts that are not formal and some propositions that are substantially informative about the 

world. The theses of the transcendental idealism of Immanuel Kant (1720–1804), the general 

scientific conservation laws, the basic principles of morality and theology, and the causal laws of 

nature have all been held by partial empiricists to be both “synthetic” (substantially informative) 

and a priori. As noted above, philosophers who embrace the Kripkean notion of reference fixing 

would add to this class propositions such as “heat is the cause of sensations of warmth” and 

“Aristotle was the teacher of Alexander the Great,” both of which derive their presumed 

aprioricity from the hypothetical circumstances in which their subject terms were introduced. At 

any rate, in all versions of partial empiricism there remain a great many straightforwardly a 

posteriori concepts and propositions: ordinary singular propositions about matters of fact and the 

concepts that figure in them are held to fall in this domain. 

14.3 Historical Background to Empiricism 

The English term empirical derives from the Ancient Greek word ἐμπειρία, empeiria, which is 

cognate with and translates to the Latin experientia, from which the 

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127 
 

words experience and experiment are derived.301 A central concept in science and the scientific 

method is that conclusions must be empirically based on the evidence of the senses. 

Both natural and social sciences use working hypotheses that 

are testable by observation and experiment. The term semi-empirical is sometimes used to 

describe theoretical methods that make use of basic axioms, established scientific laws, and 

previous experimental results in order to engage in reasoned model building and theoretical 

inquiry. 

14.3.1 Ancient Philosophy 

 

So-called common sense might appear to be inarticulately empiricist; and empiricism might be 

usefully thought of as a critical force resisting the pretensions of a more speculative 

rationalist philosophy. In the ancient world the kind of rationalism that many empiricists oppose 

was developed by Plato (c. 428–c. 328 BCE), the greatest of rationalist philosophers. The ground 

was prepared for him by three earlier bodies of thought: the Ionian cosmologies of the 6th 

century BCE, with their distinction between sensible appearance and a reality accessible only to 

pure reason; the philosophy of Parmenides (early 5th century BCE), the important early monist, 

in which purely rational argument is used to prove that the world is really an unchanging unity; 

and Pythagoreanism, which, holding that the world is really made of numbers, took mathematics 

to be the repository of ultimate truth. 

 

The first empiricists in Western philosophy were the Sophists, who rejected such rationalist 

speculation about the world as a whole and took humanity and society to be the proper objects of 

philosophical inquiry. Invoking skeptical arguments to undermine the claims of pure reason, they 

posed a challenge that invited the reaction that comprised Plato’s philosophy. 

 

Plato, and to a lesser extent Aristotle, were both rationalists. But Aristotle’s successors in the 

ancient Greek schools of Stoicism and Epicureanism advanced an explicitly empiricist account 

of the formation of human concepts. For the Stoics the human mind is at birth a clean slate, 

which comes to be stocked with concepts by the sensory impingement of the material world 

upon it. Yet they also held that there are some concepts or beliefs, the “common notions,” that 

are present to the minds of all humans; and these soon came to be conceived in a nonempirical 

way. The empiricism of the Epicureans, however, was more pronounced and consistent. For 

them human concepts are memory images, the mental residues of previous sense experience, and 

knowledge is as empirical as the ideas of which it is composed. 

 

 

 

 

                                                             
301“Definition of EMPIRIC,” www.merriam-webster.com. 

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128 
 

14.3.2 Medieval Philosophy 

 

Most medieval philosophers after St. Augustine (354–430) took an empiricist position, at least 

about concepts, even if they recognized much substantial but nonempirical knowledge. The 

standard formulation of this age was: “There is nothing in the intellect that was not previously in 

the senses.” Thus St. Thomas Aquinas (1225–74) rejected innate ideas altogether. Both soul and 

body participate in perception, and all ideas are abstracted by the intellect from what is given to 

the senses. Human ideas of unseen things, such as angels and demons and even God, are derived 

by analogy from the seen. 

The 13th-century scientist Roger Bacon emphasized empirical knowledge of the natural world 

and anticipated the polymath Renaissance philosopher of science Francis Bacon (1561–1626) in 

preferring observation to deductive reasoning as a source of knowledge. The empiricism of the 

14th-century Franciscan nominalist William of Ockham was more systematic. All knowledge of 

what exists in nature, he held, comes from the senses, though there is, to be sure, “abstractive 

knowledge” of necessary truths; but this is merely hypothetical and does not imply the existence 

of anything. His more extreme followers extended his line of reasoning toward a radical 

empiricism, in which causation is not a rationally intelligible connection between events but 

merely an observed regularity in their occurrence. 

 

14.3.3 Modern Philosophy 

 

In the earlier and unsystematically speculative phases of Renaissance philosophy, the claims of 

Aristotelian logic to yield substantial knowledge were attacked by several 16th-century 

logicians; in the same century, the role of observation was also stressed. One mildly skeptical 

Christian thinker, Pierre Gassendi (1592–1655), advanced a deliberate revival of the empirical 

doctrines of Epicurus. But the most important defender of empiricism was Francis Bacon, who, 

though he did not deny the existence of a priori knowledge, claimed that, in effect, the only 

knowledge that is worth having (as contributing to the relief of the human condition) is 

empirically based knowledge of the natural world, which should be pursued by the systematic—

indeed almost mechanical—arrangement of the findings of observation and is best undertaken in 

the cooperative and impersonal style of modern scientific research. Bacon was, in fact, the first 

to formulate the principles of scientific induction. 

 

A materialist and nominalist, Thomas Hobbes (1588–1679) combined an extreme empiricism 

about concepts, which he saw as the outcome of material impacts on the bodily senses, with an 

extreme rationalism about knowledge, of which he took geometry to be the paradigm. For him 

all genuine knowledge is a priori, a matter of rigorous deduction from definitions. The senses 

provide ideas; but all knowledge comes from “reckoning,” from deductive calculations carried 

out on the names that the thinker has assigned to them. Yet all knowledge also concerns material 

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129 
 

and sensible existences, since everything that exists is a body.302 On the other hand, many of the 

most important claims of Hobbes’s ethics and political philosophy certainly seem to be a 

posteriori, insofar as they rely heavily on his experience of human beings and the ways in which 

they interact. 

 

The most elaborate and influential presentation of empiricism was made by John Locke (1632–

1704), an early Enlightenment philosopher, in the first two books of his Essay Concerning 

Human Understanding (1690). All knowledge, he held, comes from sensation or from reflection, 

by which he meant the introspective awareness of the workings of one’s own mind. Locke often 

seemed not to separate clearly the two issues of the nature of concepts and the justification of 

beliefs. His Book I, though titled “Innate Ideas,” is largely devoted to refuting innate knowledge. 

Even so, he later admitted that much substantial knowledge—in particular, that of mathematics 

and morality—is a priori. He argued that infants know nothing; that if humans are said to know 

innately what they are capable of coming to know, then all knowledge is, trivially, innate; and 

that no beliefs whatever are universally accepted. 

 

Locke was more consistent about the empirical character of all concepts, and he described in 

detail the ways in which simple ideas can be combined to form complex ideas of what has not in 

fact been experienced. One group of dubiously empirical concepts—those of unity, existence, 

and number—he took to be derived both from sensation and from reflection. But he allowed one 

a priori concept—that of substance—which the mind adds, seemingly from its own resources, to 

its conception of any regularly associated group of perceptible qualities.303 

 

Bishop George Berkeley (1685–1753), a theistic idealist and opponent of materialism, applied 

Locke’s empiricism about concepts to refute Locke’s account of human knowledge of the 

external world. Because Berkeley was convinced that in sense experience one is never aware of 

anything but what he called “ideas” (mind-dependent qualities), he drew and embraced the 

inevitable conclusion that physical objects are simply collections of perceived ideas, a position 

that ultimately leads to phenomenalism—i.e., to the view that propositions about physical reality 

are reducible to propositions about actual and possible sensations. He accounted for 

the continuity and orderliness of the world by supposing that its reality is upheld in the 

perceptions of an unsleeping God. The theory of spiritual substance involved in Berkeley’s 

position seems to be vulnerable, however, to most of the same objections as those that he posed 

against Locke. Although Berkeley admitted that he did not have an idea of mind (either his own 

or the mind of God), he claimed that he was able to form what he called a “notion” of it. It is not 

clear how to reconcile the existence of such notions with a thoroughgoing empiricism about 

concepts. 

                                                             
302 H.C. Ezebuilo, “Locke, Berkeley and Hume: A Brief Survey of Empiricism,” International Journal of Research in 
Education, Humanities and Commerce 1(2), (2020). 
303 Ibid. 

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130 
 

 

The Scottish skeptical philosopher David Hume (1711–76) fully elaborated Locke’s empiricism 

and used it reductively to argue that there can be no more to the concepts of body, mind, and 

causal connection than what occurs in the experiences from which they arise. Like Berkeley, 

Hume was convinced that perceptions involve no constituents that can exist independently of the 

perceptions themselves. Unlike Berkeley, he could find neither an idea nor a notion of mind or 

self, and as a result his radical empiricism contained an even more parsimonious view of what 

exists. While Berkeley thought that only minds and their ideas exist, Hume thought that only 

perceptions exist and that it is impossible to form an idea of anything that is not a perception or a 

complex of perceptions. For Hume all necessary truth is formal or conceptual, determined by the 

various relations that hold between ideas. 

 

An attempt to resolve the controversy between empiricists and their opponents was made in 

the transcendental idealism of Kant, who drew upon both Hume and Gottfried Wilhelm 

Leibniz (1646–1716). With the dictum that, although all knowledge begins with experience it 

does not all arise from experience, he established a clear distinction between the innate and the a 

priori. He held that there are a priori concepts, or categories—substance and cause being the 

most important—and also substantial or synthetic a priori truths. Although not derived from 

experience, the latter apply to experience. A priori concepts and propositions do not relate to a 

reality that transcends experience; they reflect, instead, the mind’s way of organizing 

the amorphous mass of sense impressions that flow in upon it. 

 

Lockean empiricism prevailed in 19th-century England until the rise of Hegelianism in the last 

quarter of the century. To be sure, the Scottish philosophers who followed Hume but avoided his 

skeptical conclusions insisted that humans do have substantial a priori knowledge. But the 

philosophy of John Stuart Mill (1806–1873) is thoroughly empiricist. He held that all knowledge 

worth having, including mathematics, is empirical. The apparent necessity and aprioricity of 

mathematics, according to Mill, is the result of the unique massiveness of its empirical 

confirmation. All real knowledge for Mill is inductive and empirical, and deduction is sterile. It 

is not clear that Mill consistently adhered to this position, however. In both his epistemology and 

his ethics, he sometimes seemed to recognize the need for first principles that could be known 

without proof.304 The philosopher of evolution Herbert Spencer (1820–1903) offered 

another explanation of the apparent necessity of some beliefs: they are the well-attested (or 

naturally selected) empirical beliefs inherited by living humans from their evolutionary 

ancestors. Two important mathematicians and pioneers in the philosophy of modern 

physics, William Kingdon Clifford (1845–1879) and Karl Pearson (1857–1936), defended 

radically empiricist philosophies of science, anticipating the logical empiricism of the 20th 

century. 

 

                                                             
304 Ibid. 

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131 
 

14.3.4 Contemporary Philosophy 

 

One of the most influential empiricists of the 20th century was the great British philosopher and 

logician Bertrand Russell (1872–1970). Early in his career Russell admitted both synthetic a 

priori knowledge and concepts of unobservable entities. Later, through discussions with his 

pupil Ludwig Wittgenstein (1889–1951), Russell became convinced that the truths of logic and 

mathematics are analytic and that logical analysis is the essence of philosophy. In his empiricist 

phase, Russell analyzed concepts in terms of what one is “directly acquainted” with in 

experience (where experience was construed broadly enough to include not only awareness of 

sense data but also awareness of properties construed as universals). In his neutral monist phase, 

he tried to show that even the concepts of formal logic are ultimately empirical, though the 

experience that supplies them may be introspective instead of sensory. 

 

Doctrines developed by Russell and Wittgenstein influenced the German-American 

philosopher Rudolf Carnap (1891–1970) and the Vienna Circle, a discussion group in which the 

philosophy of logical positivism was developed. The empirical character of logical positivism is 

especially evident in its formulation of what came to be known as the “verification principle,” 

according to which a sentence is meaningful only if it is either tautologous or in principle 

verifiable on the basis of sense experience. 

 

Later developments in epistemology served to make some empiricist ideas about knowledge and 

justification more attractive. One of the traditional problems faced by more radical forms of 

empiricism was that they seemed to provide too slender a foundation upon which to justify what 

humans think they know.305 If sensations can occur in the absence of physical objects, for 

example, and if what one knows immediately is only the character of one’s own sensations, how 

can one legitimately infer knowledge of anything else? Hume argued that the existence of a 

sensation is not a reliable indicator of anything other than itself. In contrast, adherents of a 

contemporary school of epistemology known as “externalism” have argued that sensations (and 

other mental states) can play a role in justifying what humans think they know, even though the 

vast majority of humans are unaware of what that role is. The idea behind one form of 

externalism, “reliablism,” is that a belief is justified when it is produced through a reliable 

process, namely a process that reliably produces true beliefs. Humans may be evolutionarily 

conditioned to respond to certain kinds of sensory stimuli with a host of generally true, and 

justified, beliefs about their environment. Thus, within the framework of externalist 

epistemology, empiricism might not lead so easily to skepticism. 

 

In summary, philosophical empiricists hold no knowledge to be properly inferred or deduced 

unless it is derived from one’s sense-based experience. This view is commonly contrasted 

                                                             
305 Ibid. 

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132 
 

with rationalism, which states that knowledge may be derived from reason independently of the 

senses. For example, John Locke held that some knowledge (such as knowledge of God’s 

existence) could be arrived at through intuition and reasoning alone.306 Similarly Robert Boyle, a 

prominent advocate of the experimental method, held that we have innate ideas.307 The main 

continental rationalists (Descartes, Spinoza, and Leibniz) were also advocates of the empirical 

scientific method.308 

Between 600 and 200 BC, the Vaisheshika school of Hindu philosophy, founded by the ancient 

Indian philosopher Kanada, accepted perception and inference as the only two reliable sources of 

knowledge.309 The Charvaka school held similar beliefs, asserting that perception is the only 

reliable source of knowledge while inference obtains knowledge with uncertainty. The earliest 

Western proto-empiricists were the empiric school of ancient Greek medical practitioners, 

founded in 330 BC.310 Its members rejected the three doctrines of the dogmatic school, preferring 

to rely on the observation of phantasiai (i.e., phenomena, the appearances).The Empiric school 

was closely allied with Pyrrhonist school of philosophy, which made the philosophical case for 

their proto-empiricism. 

The notion of tabula rasa (clean slate or blank tablet) connotes a view of mind as an originally 

blank or empty recorder (Locke used the words “white paper") on which experience leave mark. 

This deny that humans have innate ideas. The notion dates back to Aristotle (c. 350 BC): “What 

the mind (nous) thinks must be in it in the same sense as letters are on a tablet (grammateion) 

which bears no actual writing (grammenon); this is just what happens in the case of the mind.”311 

Aristotle’s explanation of how this was possible was not strictly empiricist in a modern sense, 

but rather based on his theory of potentiality and actuality, and experience of sense perceptions 

still requires the help of the active nous. These notions contrasted with Platonic notions of the 

human mind as an entity that pre-existed somewhere in the heavens/world of form, before being 

sent down to join a body on Earth.312 Aristotle was considered to give a more important position 

to sense perception than Plato, and commentators in the Middle Ages summarized one of his 

positions as “nihil in intellectu nisi prius fuerit in sensu” (Latin for “nothing in the intellect 

without first being in the senses”). 

This idea was later developed in ancient philosophy by the stoic school, from about 330 BC. 

Stoic epistemology generally emphasized that the mind starts blank, but acquires knowledge as 

                                                             
306 Luis E.  Loeb, From Descartes to Hume: Continental Metaphysics and the Development of Modern Philosophy 
(Ithaca, Cornell University Press, 1981), 56. 
307 Ibid. 
308 Ibid. 
309 See D.P.S. Bhawuk, Spirituality and Indian Psychology, Anthony Marsella (ed.), (Indianapolis: Springer, 
2011),172. 
310“Greek Medicine: Alexander the Great,” www.greekmedicine.net. 
311 Aristotle, On the Soul, 3.4.430a1 
312 see Plato’s Phaedo and Apolog. 

https://en.wikipedia.org/wiki/Rationalism
https://en.wikipedia.org/wiki/Reason
https://en.wikipedia.org/wiki/John_Locke
https://en.wikipedia.org/wiki/Intuition_(knowledge)
https://en.wikipedia.org/wiki/Robert_Boyle
https://en.wikipedia.org/wiki/Rationalist
https://en.wikipedia.org/wiki/Descartes
https://en.wikipedia.org/wiki/Spinoza
https://en.wikipedia.org/wiki/Gottfried_Wilhelm_Leibniz
https://en.wikipedia.org/wiki/Vaisheshika
https://en.wikipedia.org/wiki/Dar%C5%9Bana
https://en.wikipedia.org/wiki/Kanada_(philosopher)
https://en.wikipedia.org/wiki/Perception
https://en.wikipedia.org/wiki/Inference
https://en.wikipedia.org/wiki/Charvaka
https://en.wikipedia.org/wiki/Empiric_school
https://en.wikipedia.org/wiki/Dogmatic_school
https://en.wikipedia.org/wiki/Phantasiai
https://en.wikipedia.org/wiki/Pyrrhonism
https://en.wikipedia.org/wiki/Tabula_rasa
https://en.wikipedia.org/wiki/Innate_ideas
https://en.wikipedia.org/wiki/Aristotle
https://en.wikipedia.org/wiki/Nous
https://en.wikipedia.org/wiki/Potentiality_and_actuality
https://en.wikipedia.org/wiki/Active_intellect
https://en.wikipedia.org/wiki/Platonism
https://en.wikipedia.org/wiki/Plato
https://en.wikipedia.org/wiki/Stoicism
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133 
 

the outside world is impressed upon it.313 The doxographer Aetius summarizes this view as 

“When a man is born, the Stoics say, he has the commanding part of his soul like a sheet of paper 

ready for writing upon.”314 

During the Middle Ages (from the 5th to the 15th century BC) Aristotle’s theory of tabula 

rasa was developed by Islamic philosophers starting with Al Farabi (c. 872 – 951 BC), 

developing into an elaborate theory by Avicenna (c. 980 – 1037)and demonstrated as a thought 

experiment by Ibn Tufail. For Avicenna (Ibn Sina), for example, the tabula rasa is a pure 

potentiality that is actualized through education, and knowledge is attained through empirical 

familiarity with objects in this world from which one abstracts universal concepts developed 

through a syllogistic method of reasoning in which observations lead to propositional statements 

which when compounded lead to further abstract concepts315. The intellect itself develops from 

a material intellect, which is a potentiality that can acquire knowledge to the active intellect, the 

state of the human intellect in conjunction with the perfect source of knowledge.316 So the 

immaterial active intellect, separate from any individual person, is still essential for 

understanding to occur. 

In the 12th century CE, the Andalusian Muslim philosopher and novelist Abu Bakr Ibn 

Tufail included the theory of tabula rasa as a thought experiment in his Arabic philosophical 

novel, Hayy ibn Yaqdhan in which he depicted the development of the mind of a feral 

child “from a tabula rasa to that of an adult, in complete isolation from society” on a desert 

island, through experience alone. The Latin translation of his philosophical novel, 

entitled Philosophus Autodidactus, published by Edward Pococke the Younger in 1671, had an 

influence on John Locke’s formulation of tabula rasa in An Essay Concerning Human 

Understanding.317 

A similar Islamic theological novel, Theologus Autodidactus, was written by the Arab theologian 

and physician Ibn al-Nafis in the 13th century. It also dealt with the theme of empiricism through 

the story of a feral child on a desert island, but departed from its predecessor by depicting the 

development of the protagonist’s mind through contact with society rather than in isolation from 

society.318 During the 13th century Thomas Aquinas adopted the Aristotelian position that the 

senses are essential to the mind into scholasticism; while Bonaventure (1221–1274), one of 

Aquinas’ strongest intellectual opponents, offered some of the strongest arguments in favour of 

the Platonic idea of the mind. 

                                                             
313Jeffrey Bardzell, Speculative Grammar and Stoic Language Theory in Medieval Allegorical Narrative: From 
Prudentius to Alan of Lille (New York: Routledge, 2014), 18–19. 
314Diels-Kranz, A.A. Long and D.N. Sedley (trans.), The Hellenistic Philosophers (Vol. 1) (Cambridge, Ma: Cambridge, 
1987), 238. 
315Sajjad H. Rizvi (2006), “Avicenna/Ibn Sina (c. 980–1037),” Internet Encyclopedia of Philosophy. 
316 Ibid. 
317G. A. Russell, The ‘Arabick’ Interest of the Natural Philosophers in Seventeenth-Century England (New York: Brill 
Publishers, 1994), 224. 
318 Ibid. 

https://en.wikipedia.org/wiki/Aetius_(philosopher)
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https://en.wikipedia.org/wiki/Avicenna
https://en.wikipedia.org/wiki/Thought_experiment
https://en.wikipedia.org/wiki/Thought_experiment
https://en.wikipedia.org/wiki/Ibn_Tufail
https://en.wikipedia.org/wiki/Avicenna
https://en.wikipedia.org/wiki/Education
https://en.wikipedia.org/wiki/Syllogism
https://en.wikipedia.org/wiki/Reasoning
https://en.wikipedia.org/wiki/Intellect
https://en.wikipedia.org/wiki/Passive_intellect
https://en.wikipedia.org/wiki/Potentiality
https://en.wikipedia.org/wiki/Active_intellect
https://en.wikipedia.org/wiki/Al-Andalus
https://en.wikipedia.org/wiki/Muslim
https://en.wikipedia.org/wiki/Ibn_Tufail
https://en.wikipedia.org/wiki/Ibn_Tufail
https://en.wikipedia.org/wiki/Thought_experiment
https://en.wikipedia.org/wiki/Arabic_literature
https://en.wikipedia.org/wiki/Arabic_literature
https://en.wikipedia.org/wiki/Hayy_ibn_Yaqdhan
https://en.wikipedia.org/wiki/Feral_child
https://en.wikipedia.org/wiki/Feral_child
https://en.wikipedia.org/wiki/Desert_island
https://en.wikipedia.org/wiki/Desert_island
https://en.wikipedia.org/wiki/Latin
https://en.wikipedia.org/wiki/Philosophical_novel
https://en.wikipedia.org/wiki/Edward_Pococke
https://en.wikipedia.org/wiki/John_Locke
https://en.wikipedia.org/wiki/An_Essay_Concerning_Human_Understanding
https://en.wikipedia.org/wiki/An_Essay_Concerning_Human_Understanding
https://en.wikipedia.org/wiki/Islamic_theology
https://en.wikipedia.org/wiki/Theologus_Autodidactus
https://en.wikipedia.org/wiki/Ibn_al-Nafis
https://en.wikipedia.org/wiki/Thomas_Aquinas
https://en.wikipedia.org/wiki/Aristotelianism
https://en.wikipedia.org/wiki/Scholasticism
https://en.wikipedia.org/wiki/Bonaventure
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In the late renaissance, various writers began to question 

the medieval and classical understanding of knowledge acquisition in a more fundamental way. 

In political and historical writing Niccolò Machiavelli and his friend Francesco 

Guicciardini initiated a new realistic style of writing. Machiavelli in particular was scornful of 

writers on politics who judged everything in comparison to mental ideals and demanded that 

people should study the effectual truth instead. Their contemporary, Leonardo da Vinci (1452–

1519) said, “If you find from your own experience that something is a fact and it contradicts 

what some authority has written down, then you must abandon the authority and base your 

reasoning on your own findings.”319 

Significantly, an empirical metaphysical system was developed by the Italian 

philosopher Bernardino Telesio which had an enormous impact on the development of later 

British philosophers such as Francis Bacon, who regarded Telesio as “the first of the 

moderns.”320Telesio’s influence can also be seen on the French philosophers René 

Descartes and Pierre Gassendi.321 

The decidedly anti-Aristotelian and anti-clerical music theorist Vincenzo Galilei (c.1520– 1591), 

father of Galileo and the inventor of monody, made use of the method in successfully solving 

musical problems, firstly, of tuning such as the relationship of pitch to string tension and mass in 

stringed instruments, and to the volume of air in wind instruments; and secondly to composition, 

by his various suggestions to composers. The Italian word he used for “experiment” 

was esperienza. It is known that he was the essential pedagogical influence upon the young 

Galileo, his eldest son, arguably one of the most influential empiricists in history. Vincenzo, 

through his tuning research, found the underlying truth at the heart of the misunderstood myth of 

‘Pythagoras’ hammers’ (the square of the numbers concerned yielded those musical intervals, 

not the actual numbers, as believed), and through this and other discoveries that demonstrated the 

fallibility of traditional authorities, a radically empirical attitude developed, passed on to Galileo, 

which regarded “experience and demonstration” as the sine qua non of valid rational enquiry. 

14.4 British Empiricism 

British empiricism, a retrospective characterization, emerged during the 17th century as an 

approach to early modern philosophy and modern science. Although integral to this overarching 

transition, Francis Bacon, in England, advanced empiricism at 1620, whereas René Descartes, in 

France, upheld rationalism around 1640, a distinction drawn by Immanuel Kant, in 

Germany, near 1780. Contributing later in the 17th century, Thomas Hobbes and Baruch 

Spinoza are retrospectively identified likewise as an empiricist and a rationalist, respectively. In 

the Enlightenment during the 18th century, both George Berkeley, in England, and David Hume, 

                                                             
319Camillia Matuk, “Seeing the Body: The Divergence of Ancient Chinese and Western Medical Illustration,” Journal 
of Bio-communication, Vol. 32(1), (2006), 1.  
320 Michaela Boenke, “Bernardino Telesio,” The Stanford Encyclopedia of Philosophy  Edward N. Zalta (ed.), (2018), 
URL = <https://plato.stanford.edu/archives/win2018/entries/telesio/>. 
321 Ibid. 

https://en.wikipedia.org/wiki/Renaissance
https://en.wikipedia.org/wiki/Medieval
https://en.wikipedia.org/wiki/Classical_philosophy
https://en.wikipedia.org/wiki/Niccol%C3%B2_Machiavelli
https://en.wikipedia.org/wiki/Francesco_Guicciardini
https://en.wikipedia.org/wiki/Francesco_Guicciardini
https://en.wikipedia.org/wiki/Leonardo_da_Vinci
https://en.wikipedia.org/wiki/Bernardino_Telesio
https://en.wikipedia.org/wiki/Francis_Bacon
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Pierre_Gassendi
https://en.wikipedia.org/wiki/Vincenzo_Galilei
https://en.wikipedia.org/wiki/Galileo_Galilei
https://en.wikipedia.org/wiki/Monody
https://en.wikipedia.org/wiki/Pythagorean_hammers
https://en.wikipedia.org/wiki/Early_modern_philosophy
https://en.wikipedia.org/wiki/Modern_science
https://en.wikipedia.org/wiki/Francis_Bacon
https://en.wikipedia.org/wiki/Novum_Organum
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Meditations_on_First_Philosophy
https://en.wikipedia.org/wiki/Immanuel_Kant
https://en.wikipedia.org/wiki/Critique_of_Pure_Reason
https://en.wikipedia.org/wiki/Thomas_Hobbes
https://en.wikipedia.org/wiki/Baruch_Spinoza
https://en.wikipedia.org/wiki/Baruch_Spinoza
https://en.wikipedia.org/wiki/The_Enlightenment
https://en.wikipedia.org/wiki/George_Berkeley
https://en.wikipedia.org/wiki/David_Hume
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135 
 

in Scotland, became leading exponents of empiricism, a lead precedented in the late 17th century 

by John Locke, also in England, hence the dominance of empiricism in British philosophy. 

14.4.1 John Locke 

In response to the early-to-mid-17th century continental rationalism, John Locke (1632–1704) 

proposed in An Essay Concerning Human Understanding (1689) a very influential view wherein 

the only knowledge humans can have is a posteriori, that is, based upon experience. Locke is 

famously attributed with holding the proposition that the human mind is a tabula rasa, a “blank 

tablet,” in Locke’s words “white paper,” on which the experiences derived from sense 

impressions as a person’s life proceeds are written. There are two sources of our ideas: sensation 

and reflection. In both cases, a distinction is made between simple and complex ideas. The 

former are unanalysable, and are broken down into primary and secondary qualities. Primary 

qualities are essential for the object in question to be what it is. Without specific primary 

qualities, an object would not be what it is. For example, an apple is an apple because of the 

arrangement of its atomic structure. If an apple were structured differently, it would cease to be 

an apple. Secondary qualities are the sensory information we can perceive from its primary 

qualities. For example, an apple can be perceived in various colours, sizes, and textures but it is 

still identified as an apple. Therefore, its primary qualities dictate what the object essentially is, 

while its secondary qualities define its attributes. Complex ideas combine simple ones, and 

dividethem into substances, modes, and relations. According to Locke, our knowledge of things 

is a perception of ideas that are in accordance or discordance with each other, which is very 

different from the quest for certainty of Descartes. 

14.4.2 George Berkeley  

A generation later, the Irish Anglican bishop, George Berkeley (1685–1753), determined that 

Locke’s view immediately opened a door that would lead to eventual atheism. In response to 

Locke, he put forth in his Treatise Concerning the Principles of Human Knowledge (1710) an 

important challenge to empiricism in which things only exist either as a result of their being 

perceived, or by virtue of the fact that they are an entity doing the perceiving. (For Berkeley, 

God fills in for humans by doing the perceiving whenever humans are not there to do it.) In his 

text Alciphron, Berkeley maintained that any order humans may see in nature is the language or 

handwriting of God.322 Berkeley’s approach to empiricism would later come to be 

called subjective idealism. 

14.4.3 David Hume 

The Scottish philosopher David Hume (1711–1776) responded to Berkeley’s criticisms of Locke, 

as well as other differences between early modern philosophers, and moved empiricism to a new 

level of skepticism. Hume argued in keeping with the empiricist view that all knowledge is 

derived from sense experience, but he accepted that this has implications not normally acceptable 

to philosophers. He wrote, for example: Locke divides all arguments into demonstrative and 

                                                             
322Thornton Stephen “Berkeley’s Theory of Reality” in The Journal of the Limerick Philosophical Society, 1987, 60. 

https://en.wikipedia.org/wiki/Scotland
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https://en.wikipedia.org/wiki/Continental_rationalism
https://en.wikipedia.org/wiki/John_Locke
https://en.wikipedia.org/wiki/An_Essay_Concerning_Human_Understanding
https://en.wikipedia.org/wiki/A_posteriori
https://en.wikipedia.org/wiki/Tabula_rasa
https://en.wikipedia.org/wiki/Certainty
https://en.wikipedia.org/wiki/Descartes
https://en.wikipedia.org/wiki/Bishop_George_Berkeley
https://en.wikipedia.org/wiki/Anglican
https://en.wikipedia.org/wiki/George_Berkeley
https://en.wikipedia.org/wiki/Atheism
https://en.wikipedia.org/wiki/Treatise_Concerning_the_Principles_of_Human_Knowledge
https://en.wikipedia.org/wiki/Alciphron_(book)
https://en.wikipedia.org/wiki/Subjective_idealism
https://en.wikipedia.org/wiki/David_Hume
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136 
 

probable. On this view, we must say that it is only probable that all men must die or that the sun 

will rise to-morrow, because neither of these can be demonstrated. But to conform our language 

more to common use, we ought to divide arguments into demonstrations, proofs, and 

probabilities—by ‘proofs’ meaning arguments from experience that leave no room for doubt or 

opposition.323 

And: 

I believe the most general and most popular explication of 

this matter, is to say, that finding from experience, that 

there are several new productions in matter, such as the 

motions and variations of body, and concluding that there 

must somewhere be a power capable of producing them, we 

arrive at last by this reasoning at the idea of power and 

efficacy. But to be convinced that this explication is more 

popular than philosophical, we need but reflect on two very 

obvious principles. First, That reason alone can never give 

rise to any original idea, and secondly, that reason, as 

distinguished from experience, can never make us 

conclude, that a cause or productive quality is absolutely 

requisite to every beginning of existence. Both these 

considerations have been sufficiently explained: and 

therefore shall not at present be any farther insisted on.324 

Hume divided all of human knowledge into two categories: relations of ideas and matters of fact. 

Mathematical and logical propositions (e.g. “that the square of the hypotenuse is equal to the 

sum of the squares of the two sides”) are examples of the first, while propositions involving 

some contingent observation of the world (e.g. “the sun rises in the East”) are examples of the 

second. All of people’s ideas, in turn, are derived from their “impressions.” For Hume, an 

impression corresponds roughly with what we call a sensation. To remember or to imagine such 

impressions is to have an idea. Ideas are therefore the faint copies of sensations.325 

Hume maintained that no knowledge, even the most basic beliefs about the natural world, can be 

conclusively established by reason. Rather, he maintained, our beliefs are more a result of 

accumulated habits, developed in response to accumulated sense experiences.326 Among his 

many arguments Hume also added another important slant to the debate about scientific 

method—that of the problem of induction. He argued that it requires inductive reasoning to 

arrive at the premises for the principle of inductive reasoning, and therefore the justification for 

                                                             
323 D. Hume. “Of Probability,” Enquiries Concerning the Human Understanding and Concerning the Principles of 
Morals (Oxford: Clarendon Press, 1975). 
324 Ibid., “Of the Idea of a Necessary Connexion.” 
325 Cf. H.C. Ezebuilo, “Locke, Berkeley and Hume, 96-99. 
326 Ibid. 

https://en.wikipedia.org/wiki/Contingent
https://en.wikipedia.org/wiki/Scientific_method
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https://en.wikipedia.org/wiki/Problem_of_induction
https://en.wikipedia.org/wiki/Inductive_reasoning
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inductive reasoning is a circular argument.327Among Hume’s conclusions regarding the problem 

of induction is that there is no certainty that the future will resemble the past. Thus, as a simple 

instance posed by Hume, we cannot know with certainty by inductive reasoning that the sun will 

continue to rise in the East, but instead come to expect it to do so because it has repeatedly done 

so in the past. 

Hume concluded that such things as belief in an external world and belief in the existence of the 

self were not rationally justifiable. According to Hume these beliefs were to be accepted 

nonetheless because of their profound basis in instinct and custom. His lasting legacy, however, 

was the doubt that his skeptical arguments cast on the legitimacy of inductive reasoning, 

allowing many skeptics who followed to cast similar doubt. 

14.4.3 Phenomenalism 

Most of Hume’s followers have disagreed with his conclusion that belief in an external world 

is rationally unjustifiable, contending that Hume’s own principles implicitly contained the 

rational justification for such a belief, that is, beyond being content to let the issue rest on human 

instinct, custom and habit.328 According to an extreme empiricist theory known 

as phenomenalism, anticipated by the arguments of both Hume and George Berkeley, a physical 

object is a kind of construction out of our experiences. Phenomenalism is the view that physical 

objects, properties, events (whatever is physical) are reducible to mental objects, properties, 

events. Ultimately, only mental objects, properties, events, exist—hence the closely related 

term subjective idealism. By the phenomenalistic line of thinking, to have a visual experience of 

a real physical thing is to have an experience of a certain kind of group of experiences. This type 

of set of experiences possesses a constancy and coherence that is lacking in the set of 

experiences of which hallucinations, for example, are a part. As John Stuart Mill put it in the 

mid-19th century, matter is the “permanent possibility of sensation.”329 Mill’s empiricism went a 

significant step beyond Hume in still another respect: in maintaining that induction is necessary 

for all meaningful knowledge including mathematics. As summarized by D.W. Hamlin: 

Mill claimed that mathematical truths were merely very 

highly confirmed generalizations from experience; 

mathematical inference, generally conceived as deductive 

[and a priori] in nature, Mill set down as founded on 

induction. Thus, in Mill's philosophy there was no real 

place for knowledge based on relations of ideas. In his view 

logical and mathematical necessity is psychological; we are 

merely unable to conceive any other possibilities than those 

that logical and mathematical propositions assert. This is 

                                                             
327 Ibid. 
328 H. Morick, Challenges to Empiricism (Indianapolis: Hackett Publishing, 1980), 14. 
329 J.S. Mill, “An Examination of Sir William Rowan Hamilton's Philosophy,” in A.J. Ayer and Ramond Winch (eds.), 
British Empirical Philosophers (New York, NY: Simon and Schuster, 1968), 51-52. 

https://en.wikipedia.org/wiki/Inductive_reasoning
https://en.wikipedia.org/wiki/Phenomenalism
https://en.wikipedia.org/wiki/Subjective_idealism
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138 
 

perhaps the most extreme version of empiricism known, 

but it has not found many defenders.330 

Mill’s empiricism thus held that knowledge of any kind is not from direct experience but an 

inductive inference from direct experience. The problems other philosophers have had with 

Mill’s position center around the following issues: Firstly, Mill’s formulation encounters 

difficulty when it describes what direct experience is by differentiating only between actual and 

possible sensations. This misses some key discussion concerning conditions under which such 

“groups of permanent possibilities of sensation” might exist in the first place. Berkeley put God 

in that gap; the phenomenalists, including Mill, essentially left the question unanswered. In the 

end, lacking an acknowledgement of an aspect of reality that goes beyond mere possibilities of 

sensation, such a position leads to a version of subjective idealism. 

Questions of how floor beams continue to support a floor while unobserved, how trees continue 

to grow while unobserved and untouched by human hands, etc., remain unanswered, and perhaps 

unanswerable in these terms.331 Secondly, Mill’s formulation leaves open the unsettling 

possibility that the “gap-filling entities are purely possibilities and not actualities at 

all.”332 Thirdly, Mill’s position, by calling mathematics merely another species of inductive 

inference, misapprehends mathematics. It fails to fully consider the structure and method 

of mathematical science, the products of which are arrived at through an internally 

consistent deductive set of procedures which do not, either today or at the time Mill wrote, fall 

under the agreed meaning of induction.333 

The phenomenalist phase of post-Humean empiricism ended by the 1940s, for by that time it had 

become obvious that statements about physical things could not be translated into statements 

about actual and possible sense data.334 If a physical object statement is to be translatable into a 

sense-data statement, the former must be at least deducible from the latter. But it came to be 

realized that there is no finite set of statements about actual and possible sense-data from which 

we can deduce even a single physical-object statement. The translating or paraphrasing statement 

must be couched in terms of normal observers in normal conditions of observation. There is, 

however, no finite set of statements that are couched in purely sensory terms and can express the 

satisfaction of the condition of the presence of a normal observer. According to phenomenalism, 

to say that a normal observer is present is to make the hypothetical statement that were a doctor 

to inspect the observer, the observer would appear to the doctor to be normal. But, of course, the 

doctor himself must be a normal observer. If we are to specify this doctor's normality in sensory 

terms, we must make reference to a second doctor who, when inspecting the sense organs of the 

first doctor, would himself have to have the sense data a normal observer has when inspecting 

                                                             
330 “Empiricism,” Macmillan Encyclopedia of Philosophy, vol.2, (1969), 503. 
331 Ibid. 
332 Ibid. 
333 Ibid. 
334 John Bolender, “Factual Phenomenalism: A Supervenience Theory,” Sorites, no. 9, 16–31. 

https://en.wikipedia.org/wiki/Mathematical_science
https://en.wikipedia.org/wiki/Deductive_reasoning
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the sense organs of a subject who is a normal observer. And if we are to specify in sensory terms 

that the second doctor is a normal observer, we must refer to a third doctor, and so on.335 

 

14.5 Logical Empiricism 

Logical empiricism (also logical positivism or neopositivism) was an early 20th century attempt 

to synthesize the essential ideas of British empiricism (example, a strong emphasis on sensory 

experience as the basis for knowledge) with certain insights from mathematical logic that had 

been developed by Gottlob Frege and Ludwig Wittgenstein. Some of the key figures in this 

movement were Otto Neurath, Moritz Schlick and the rest of the Vienna Circle, along with A.J. 

Ayer, Rudolf Carnap and Hans Reichenbach. 

The neopositivists subscribed to a notion of philosophy as the conceptual clarification of the 

methods, insights and discoveries of the sciences. They saw in the logical symbolism elaborated 

by Frege (1848–1925) and Bertrand Russell (1872–1970) a powerful instrument that could 

rationally reconstruct all scientific discourse into an ideal, logically perfect, language that would 

be free of the ambiguities and deformations of natural language. This gave rise to what they saw 

as metaphysical pseudoproblems and other conceptual confusions. By combining Frege’s thesis 

that all mathematical truths are logical with the early Wittgenstein’s idea that all logical 

truths are mere linguistic tautologies, they arrived at a twofold classification of all propositions: 

the analytic (a priori) and the synthetic (a posteriori).336On this basis, they formulated a strong 

principle of demarcation between sentences that have sense and those that do not: the so-called 

“verification principle”. Any sentence that is not purely logical, or is unverifiable, is devoid of 

meaning. As a result, most metaphysical, ethical, aesthetic and other traditional philosophical 

problems came to be considered pseudoproblems.337 

In the extreme empiricism of the neopositivists, any genuinely synthetic assertion must be 

reducible to an ultimate assertion (or set of ultimate assertions) that expresses direct observations 

or perceptions. In later years, Carnap and Neurath abandoned this sort of phenomenalism in favor 

of a rational reconstruction of knowledge into the language of an objective spatio-temporal 

physics. That is, instead of translating sentences about physical objects into sense-data, such 

sentences were to be translated into so-called protocol sentences, for example, “X at 

location Y and at time T observes such and such.”338 The central theses of logical positivism 

(verificationism, the analytic–synthetic distinction, reductionism, etc.) came under sharp attack 

by thinkers such as Nelson Goodman, W.V. Quine, Hilary Putnam, Karl Popper, and Richard 

Rorty. By the late 1960s, it had become evident to most philosophers that the movement had 

                                                             
335Roderick Chisholm M., “The Problem of Empiricism,” The Journal of Philosophy, 45(19), (1948), 512–13. 
336 Peter Achinstein,  and Stephen F. Barker, The Legacy of Logical Positivism: Studies in the Philosophy of Science 
(Baltimore: Johns Hopkins University Press, 1969). 
337 Ibid. 
338 Nicholas Rescher, The Heritage of Logical Positivism (Lanham: University Press of America, 1985, 244. 

https://en.wikipedia.org/wiki/Mathematical_logic
https://en.wikipedia.org/wiki/Gottlob_Frege
https://en.wikipedia.org/wiki/Ludwig_Wittgenstein
https://en.wikipedia.org/wiki/Otto_Neurath
https://en.wikipedia.org/wiki/Moritz_Schlick
https://en.wikipedia.org/wiki/Vienna_Circle
https://en.wikipedia.org/wiki/A.J._Ayer
https://en.wikipedia.org/wiki/A.J._Ayer
https://en.wikipedia.org/wiki/Rudolf_Carnap
https://en.wikipedia.org/wiki/Hans_Reichenbach
https://en.wikipedia.org/wiki/Bertrand_Russell
https://en.wikipedia.org/wiki/Logical_truth
https://en.wikipedia.org/wiki/Logical_truth
https://en.wikipedia.org/wiki/Tautology_(logic)
https://en.wikipedia.org/wiki/Verification_principle
https://en.wikipedia.org/wiki/Nelson_Goodman
https://en.wikipedia.org/wiki/W.V._Quine
https://en.wikipedia.org/wiki/Hilary_Putnam
https://en.wikipedia.org/wiki/Karl_Popper
https://en.wikipedia.org/wiki/Richard_Rorty
https://en.wikipedia.org/wiki/Richard_Rorty
https://en.wikipedia.org/wiki/Peter_Achinstein
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pretty much run its course, though its influence is still significant among contemporary analytic 

philosophers such as Michael Dummett and other anti-realists. 

14.6 Criticism and Evaluation 

The earliest expressions of empiricism in ancient Greek philosophy were those of the Sophists. 

In reaction to them, Plato presented the rationalistic view that humans have only “opinion” about 

changing, perceptible, existing things in space and time; that “knowledge” can be had only of 

timeless, necessary truths; and that the objects of knowledge—the unchanging and 

imperceptible forms or universals (such as the Beautiful, the Just, and so on)—are the only 

things that are truly real. The circles and triangles of geometrical “knowledge,” in this view, are 

quite different in their perfect exactness from the approximately circular and triangular things 

present to human senses. In his dialogue the Phaedo, Plato expounded a theory of literally innate 

ideas; humans, for example, have a conception of exact Equality, which, since it could not have 

been supplied by the senses, must have been acquired by the soul before it was embodied.  

 

Aristotle agreed with Plato that knowledge is of the universal but held that such universal forms 

should not be conceived as “separated” from the matter embodying them. This belief does not 

make Aristotle an empiricist, though he was certainly a less extreme rationalist than Plato. 

Aristotle took the rationalist view that every science or body of knowledge must 

resemble “Euclidean geometry” in consisting of deductions from first principles that are self-

evidently and necessarily true and that, although the senses acquaint humans with the sensible 

forms of things, there cannot be knowledge of them unless reason is brought into play to 

apprehend their intelligible forms. 

The Stoic view of “common notions,” or beliefs that are held by all humans—a potentially 

rationalistic element in an otherwise empirical school of thought—was expanded during the 

early medieval period by St. Augustine, a thoroughgoing rationalist. The Stoic common notions, 

Augustine held, are truths that God has implanted in the human mind through direct illumination. 

 

Although the early modern expression of empiricism in the 17th century by Francis 

Bacon heralded the scientific age, its influence was lessened by his failure to appreciate the 

revolutionary use of mathematics that comprised the genius of Galileo’s new physics and, even 

more fundamentally, by his underestimation of the need for imaginative conjecture in the 

formation of scientific hypotheses to restrict the overwhelming number of facts that would 

otherwise have to be handled. In contrast to Bacon’s view, the philosopher and 

mathematician René Descartes (1596–1650), one of the principal founders of modern thought, 

developed a form of rationalism that was more immediately influential. For Descartes some of 

the ideas that are critically important for philosophy, mathematics, and physics are innate, and 

sense experience is at most the agency that elicits these ideas. In principle, much of human 

knowledge is a priori and demonstrable by pure reasoning, but in practice, because the human 

https://en.wikipedia.org/wiki/Analytic_philosophy
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https://en.wikipedia.org/wiki/Michael_Dummett
https://en.wikipedia.org/wiki/Anti-realism
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https://www.britannica.com/topic/innate-idea
https://www.merriam-webster.com/dictionary/conception
https://www.britannica.com/biography/Aristotle
https://www.britannica.com/topic/belief
https://www.britannica.com/science/Euclidean-geometry
https://www.britannica.com/topic/reason
https://www.britannica.com/topic/Stoicism
https://www.merriam-webster.com/dictionary/empirical
https://www.merriam-webster.com/dictionary/medieval
https://www.britannica.com/biography/Saint-Augustine
https://www.merriam-webster.com/dictionary/Stoic
https://www.britannica.com/biography/Francis-Bacon-Viscount-Saint-Alban
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https://www.merriam-webster.com/dictionary/comprised
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intellect is finite, it is necessary to rely on experience to confirm these propositions when 

rational proof is beyond reach. 

 

In England, innate ideas and knowledge were defended by Edward Lord Herbert of 

Cherbury (1582–1648), whose philosophy was a precursor of Deism, and by a school 

of Puritan humanists known as the Cambridge Platonists. The case for innate ideas, however, is 

hard to establish; there can be in the nature of the case little actual evidence that one can possess 

concepts before having had some relevant experience. 

 

In the second half of the 17th century, the empiricist views of Locke were similarly controverted 

by Leibniz,339 who examined Locke’s views in minute detail arguing that ideas can be virtually 

innate in a less trivial sense than Locke allowed. Interpreting Locke’s notion of reflection as 

reasoning rather than as introspection, Leibniz supposed that Locke was more of a rationalist 

than he really was. 

 

In contemporary philosophy, there are thinkers who, though broadly sympathetic to logical 

positivism, have voiced reservations about some of the doctrines often associated with traditional 

empiricism. One important philosopher of science, Karl Popper (1902–1994), rejected the 

inductivism that views the growth of empirical knowledge as the result of a mechanical routine 

of generalization based on experienced correlations. Popper argued that a statement is empirical 

if it is falsifiable by experience,340 that is, if there are possible experiences that would show that 

the statement is false. Given the central role that experience plays in falsification, however, 

Popper still fell squarely within the empiricist camp. 

 

An influential American philosopher and logician, W.V.O. Quine (1908–2000), was critical of 

the logical positivists’ frequent recourse to the concept of meaning and rejected the sharp 

distinction they made between analytic and synthetic truths. Quine held that human concepts and 

beliefs are the joint outcome of experience and convention, and he denied that the role of the two 

factors can be as readily distinguished as empiricists assert. 

The theory of knowledge has been one of the central disciplines of Western philosophy since the 

17th century, and its most basic issue is that between empiricism and rationalism, an issue that is 

still being actively debated. On the one hand, the idea that science rests on substantial but 

nonempirical presuppositions has been put in question by the fact that in some areas it seems to 

get along without them: without conservation in cosmology, 

without causality in quantum physics. On the other hand, the traditional theory of the innate 

powers of the mind was reanimated by the considerations underlying the theory 

of language offered by the American linguist Noam Chomsky, who holds that the learning of 

                                                             
339 Leibniz, “New Essay Concerning Human Understanding,” https://www.britannica.com/topic/new-essay-
concerning-human-understanding/ 
340 H.C. Ezebuilo, “Locke, Berkeley and Hume: A Brief Survey of Empiricism,” International Journal of Research in 
Education, Humanities and Commerce 1(2), (2020). 

https://www.britannica.com/topic/evidence-law
https://www.britannica.com/biography/Edward-Herbert-1st-Baron-Herbert-of-Cherbury
https://www.britannica.com/biography/Edward-Herbert-1st-Baron-Herbert-of-Cherbury
https://www.merriam-webster.com/dictionary/precursor
https://www.britannica.com/topic/Deism
https://www.britannica.com/topic/Puritanism
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https://www.britannica.com/topic/meaning
https://www.merriam-webster.com/dictionary/analytic
https://www.merriam-webster.com/dictionary/synthetic
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https://www.merriam-webster.com/dictionary/disciplines
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https://www.britannica.com/topic/idea
https://www.britannica.com/topic/philosophy-of-science
https://www.britannica.com/topic/causation
https://www.merriam-webster.com/dictionary/quantum
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language is far too rapid and too universal to be attributed entirely to an empirical process of 

conditioning.341 The basic strength of empiricism consists in its recognition that 

human concepts and beliefs apply to a world outside oneself, and that it is by way of the senses 

that this world acts upon the individual. The question, however, of how much the mind itself 

contributes to the task of processing its sensory input is one that has remained unanswered. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                             
341 Stephen P. Stich, Between Chomskian Rationalism and Popperian EMpericism. The British Journal for the 
Philosophy of Science 30(4), 1979,329-347. 

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CHAPTER FIFTEEN 

RATIONALISM 

15.1 What is Rationalism? 

Rationalism is the epistemological view that reason is the chief source of knowledge and the 

main determinant of what constitutes knowledge. More broadly, it can also refer to any view 

which appeals to reason as a source of knowledge or justification. Rationalism is one of the two 

classical views in epistemology, the other being empiricism. Rationalists claim that the mind, 

through the use of reason, can directly grasp certain truths in various domains, 

including logic, mathematics, ethics, and metaphysics. Rationalist views can range from modest 

views in mathematics and logic (such as that of Gottlob Frege) to ambitious metaphysical 

systems (such as that of Baruch Spinoza). Some of the most famous rationalists 

include Plato, René Descartes, Baruch Spinoza, and Gottfried Leibniz. 

Rationalism is the view that regards reason as the main source and test of knowledge. Holding 

that reality itself has an inherently logical structure, the rationalist asserts that a class 

of truths exists that the intellect can grasp directly. There are, according to the rationalists, 

certain rational principles—especially in logic and mathematics, and even 

in ethics and metaphysics—that are so fundamental that to deny them is to fall into contradiction. 

The rationalists’ confidence in reason and proof tends, therefore, to detract from their respect for 

other ways of knowing. 

Rationalism has long been the rival of empiricism, the doctrine that all knowledge comes from, 

and must be tested by, sense experience. As against this doctrine, rationalism holds reason to be 

a faculty that can lay hold of truths beyond the reach of sense perception, both in certainty and 

generality. In stressing the existence of a “natural light,” rationalism has also been the rival of 

systems claiming esoteric knowledge, whether from mystical experience, revelation, or intuition, 

and has been opposed to various irrationalisms that tend to stress the biological, the emotional or 

volitional, the unconscious, or the existential at the expense of the rational. 

 

15.2 Expressions of Rationalism 

 

Rationalism has somewhat different meanings in different fields, depending upon the kind of 

theory to which it is opposed. In the psychology of perception, for example, rationalism is in a 

sense opposed to the genetic psychology of the Swiss scholar Jean Piaget (1896–1980), who, 

exploring the development of thought and behaviour in the infant, argued that the categories of 

the mind develop only through the infant’s experience in concourse with the world. Similarly, 

rationalism is opposed to transactionalism, a point of view in psychology according to which 

human perceptual skills are achievements, accomplished through actions performed in response 

to an active environment. On this view, the experimental claim is made that perception is 

conditioned by probability judgments formed on the basis of earlier actions performed in similar 

https://en.wikipedia.org/wiki/Logic
https://en.wikipedia.org/wiki/Mathematics
https://en.wikipedia.org/wiki/Ethics
https://en.wikipedia.org/wiki/Metaphysics
https://en.wikipedia.org/wiki/Gottlob_Frege
https://en.wikipedia.org/wiki/Baruch_Spinoza
https://en.wikipedia.org/wiki/Plato
https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes
https://en.wikipedia.org/wiki/Baruch_Spinoza
https://en.wikipedia.org/wiki/Gottfried_Leibniz
https://www.britannica.com/topic/reason
https://www.britannica.com/topic/epistemology
https://www.britannica.com/topic/reality
https://www.britannica.com/topic/logic
https://www.britannica.com/topic/truth-philosophy-and-logic
https://www.britannica.com/topic/logic
https://www.britannica.com/science/mathematics
https://www.britannica.com/topic/ethics-philosophy
https://www.britannica.com/topic/metaphysics
https://www.britannica.com/topic/empiricism
https://www.britannica.com/topic/perception
https://www.merriam-webster.com/dictionary/esoteric
https://www.britannica.com/topic/mysticism
https://www.britannica.com/topic/intuition
https://www.britannica.com/topic/irrationalism
https://www.britannica.com/science/unconscious
https://www.britannica.com/topic/existentialism
https://www.britannica.com/science/psychology
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situations. As a corrective to these sweeping claims, the rationalist defends a nativism, which 

holds that certain perceptual and conceptual capacities are innate—as suggested in the case of 

depth perception by experiments with “the visual cliff,” which, though platformed over with firm 

glass, the infant perceives as hazardous—though these native capacities may at times lie dormant 

until the appropriate conditions for their emergence arise. 

In the comparative study of languages, a similar nativism was developed beginning in the 1950s 

by the linguistic theorist Noam Chomsky, who, acknowledging a debt to René Descartes (1596–

1650), explicitly accepted the rationalistic doctrine of “innate ideas.” Though the thousands of 

languages spoken in the world differ greatly in sounds and symbols, they sufficiently resemble 

each other in syntax to suggest that there is “a schema of universal grammar” determined by 

“innate presettings” in the human mind itself. These presettings, which have their basis in the 

brain, set the pattern for all experience, fix the rules for the formation of meaningful sentences, 

and explain why languages are readily translatable into one another. It should be added that what 

rationalists have held about innate ideas is not that some ideas are full-fledged at birth but only 

that the grasp of certain connections and self-evident principles, when it comes, is due to inborn 

powers of insight rather than to learning by experience. 

Common to all forms of speculative rationalism is the belief that the world is a rationally ordered 

whole, the parts of which are linked by logical necessity and the structure of which is therefore 

intelligible. Thus, in metaphysics it is opposed to the view that reality is a disjointed aggregate of 

incoherent bits and is thus opaque to reason. In particular, it is opposed to the logical 

atomisms of such thinkers as David Hume (1711–76) and the early Ludwig Wittgenstein (1889–

1951), who held that facts are so disconnected that any fact might well have been different from 

what it is without entailing a change in any other fact. Rationalists have differed, however, with 

regard to the closeness and completeness with which the facts are bound together. At the lowest 

level, they have all believed that the law of contradiction “A and not-A cannot coexist” holds for 

the real world, which means that every truth is consistent with every other; at the highest level, 

they have held that all facts go beyond consistency to a positive coherence; that is, they are so 

bound up with each other that none could be different without all being different. 

In epistemology where its claims are clearest, rationalism holds that at least some human 

knowledge is gained through a priori (prior to experience), or rational, insight as distinct from 

sense experience, which too often provides a confused and merely tentative approach. In the 

debate between empiricism and rationalism, empiricists hold the simpler and more sweeping 

position, the Humean claim that all knowledge of fact stems from perception. Rationalists, on the 

contrary, urge that some, though not all, knowledge arises through direct apprehension by the 

intellect. What the intellectual faculty apprehends is objects that transcend sense experience—

universals and their relations. A universal is an abstraction, a characteristic that may reappear in 

various instances: the number three, for example, or the triangularity that all triangles have in 

common, or the humanity that all human beings have in common. Though these cannot be seen, 

https://www.merriam-webster.com/dictionary/conceptual
https://www.britannica.com/topic/innate-idea
https://www.britannica.com/science/visual-cliff
https://www.britannica.com/topic/language
https://www.britannica.com/biography/Noam-Chomsky
https://www.britannica.com/biography/Rene-Descartes
https://www.britannica.com/topic/innate-idea
https://www.britannica.com/topic/syntax
https://www.britannica.com/topic/mind
https://www.britannica.com/topic/insight-learning
https://www.britannica.com/topic/belief
https://www.merriam-webster.com/dictionary/metaphysics
https://www.merriam-webster.com/dictionary/aggregate
https://www.merriam-webster.com/dictionary/opaque
https://www.britannica.com/topic/Logical-Atomism
https://www.britannica.com/topic/Logical-Atomism
https://www.britannica.com/biography/David-Hume
https://www.britannica.com/biography/Ludwig-Wittgenstein
https://www.britannica.com/topic/contradictories
https://www.britannica.com/topic/truth-philosophy-and-logic
https://www.britannica.com/topic/a-priori-knowledge
https://www.merriam-webster.com/dictionary/apprehension
https://www.merriam-webster.com/dictionary/intellectual
https://www.merriam-webster.com/dictionary/transcend
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heard, or felt, rationalists point out that humans can plainly think about them and about their 

relations. 

This kind of knowledge, which includes the whole of logic and mathematics as well as 

fragmentary insights in many other fields, is, in the rationalist view, the most important and 

certain knowledge that the mind can achieve. Such a priori knowledge is both necessary (that, it 

cannot be conceived as otherwise) and universal, in the sense that it admits of no exceptions. In 

the  philosophy of Immanuel Kant (1724–1804), epistemological rationalism finds expression in 

the claim that the mind imposes its own inherent categories or forms upon incipient experience. 

In ethics, rationalism holds the position that reason, rather than feeling, custom, or authority, is 

the ultimate court of appeal in judging good and bad, right and wrong. One of the most notable 

representatives of rational ethics is Kant, who held that the way to judge an act is to check its 

self-consistency as apprehended by the intellect: to note, first, what it is essentially, or in 

principle—a lie, for example, or a theft—and then to ask if one can consistently will that the 

principle be made universal. Is theft, then, right? The answer must be “No,” because, if theft 

were generally approved, people’s property would not be their own as opposed to anyone else’s, 

and theft would then become meaningless; the notion, if universalized, would thus destroy itself, 

as reason by itself is sufficient to show. 

In religion, rationalism commonly means that all human knowledge comes through the use of 

natural faculties, without the aid of supernatural revelation. “Reason” is here used in a broader 

sense, referring to human cognitive powers generally, as opposed to supernatural grace or faith—

though it is also in sharp contrast to so-called existential approaches to truth. Reason, for the 

rationalist, thus stands opposed to many of the religions of the world, including Christianity, 

which have held that the divine has revealed itself through inspired persons or writings and 

which have required, at times, that its claims be accepted as infallible, even when they do not 

accord with natural knowledge. Religious rationalists hold, on the other hand, that if the clear 

insights of human reason must be set aside in favour of alleged revelation, then human thought is 

everywhere rendered suspect—even in the reasonings of the theologians themselves. There 

cannot be two ultimately different ways of warranting truth, they assert; hence rationalism argues 

that reason, with its standard of consistency, must be the final court of appeal. Religious 

rationalism can reflect either a traditional piety, when endeavouring to display the alleged sweet 

reasonableness of religion, or an antiauthoritarian temper, when aiming to supplant religion with 

the “goddess of reason.” 

 

 

 

 

 

 

https://www.britannica.com/topic/a-priori-knowledge
https://www.britannica.com/topic/Kantianism
https://www.britannica.com/biography/Immanuel-Kant
https://www.merriam-webster.com/dictionary/inherent
https://www.merriam-webster.com/dictionary/incipient
https://www.merriam-webster.com/dictionary/ethics
https://www.britannica.com/topic/categorical-imperative
https://www.britannica.com/topic/philosophy-of-religion
https://www.britannica.com/topic/revelation
https://www.merriam-webster.com/dictionary/cognitive
https://www.britannica.com/topic/grace-religion
https://www.britannica.com/topic/faith
https://www.merriam-webster.com/dictionary/existential
https://www.britannica.com/topic/Christianity
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15.3 History of Rationalism 

 

15.3.1 Epistemological Rationalism in Ancient Philosophies 

 

The first Western philosopher to stress rationalist insight was Pythagoras, a shadowy figure of 

the 6th century BCE. Noticing that, for a right triangle, a square built on its hypotenuse equals 

the sum of those on its sides and that the pitches of notes sounded on a lute bear a mathematical 

relation to the lengths of the strings, Pythagoras held that these harmonies reflected the ultimate 

nature of reality. He summed up the implied metaphysical rationalism in the words “All 

is number.” It is probable that he had caught the rationalist’s vision, later seen by Galileo (1564–

1642), of a world governed throughout by mathematically formulable laws. 

The difficulty in this view, however, is that, working with universals and their relations, which, 

like the multiplication table, are timeless and changeless, it assumes a static world and ignores 

the particular, changing things of daily life. The difficulty was met boldly by the 

rationalist Parmenides (born c. 515 BCE), who insisted that the world really is a static whole and 

that the realm of change and motion is an illusion, or even a self-contradiction. His disciple Zeno 

of Elea (c. 495–c. 430 BCE) further argued that anything thought to be moving is confronted 

with a row of points infinite in number, all of which it must traverse; hence it can never reach its 

goal, nor indeed move at all. Of course, perception tells us that we do move, but Zeno, compelled 

to choose between perception and reason, clung to reason. 

The exalting of rational insight above perception was also prominent in Plato (c. 427–c. 

347 BCE). In the Meno, Socrates (c. 470–399 BCE) dramatized the innateness of knowledge by 

calling upon an illiterate slave boy and, drawing a square in the sand, proceeding to elicit from 

him, step by step, the proof of a theorem in geometry of which the boy could never have heard 

(to double the size of a square, draw a square on the diagonal). Such knowledge, rationalists 

insist, is certain, universal, and completely unlearned. 

Plato so greatly admired the rigorous reasoning of geometry that he is alleged to have inscribed 

over the door of his Academy the phrase “Let no one unacquainted with geometry enter here.” 

His famous forms are accessible only to reason, not to sense. But how are they related to sensible 

things? His answers differed. Sometimes he viewed the forms as distilling those common 

properties of a class in virtue of which one identifies anything as a member of it. Thus, what 

makes anything a triangle is it’s having three straight sides; this is its essence. At other times, 

Plato held that the form is an ideal, a non-sensible goal to which the sensible thing approximates; 

the geometer’s perfect triangle “never was on sea or land,” though all actual triangles more or 

less embody it. He conceived the forms as more real than the sensible things that are their 

shadows and saw that philosophers must penetrate these invisible essences and see with 

their mind’s eye how they are linked together. For Plato they formed an orderly system that was 

at once eternal, intelligible, and good. 

https://www.britannica.com/biography/Pythagoras
https://www.britannica.com/topic/harmony-philosophy
https://www.merriam-webster.com/dictionary/metaphysical
https://www.britannica.com/science/number-system
https://www.britannica.com/biography/Galileo-Galilei
https://www.britannica.com/biography/Parmenides-Greek-philosopher
https://www.merriam-webster.com/dictionary/illusion
https://www.merriam-webster.com/dictionary/disciple
https://www.britannica.com/biography/Zeno-of-Elea
https://www.britannica.com/biography/Zeno-of-Elea
https://www.merriam-webster.com/dictionary/infinite
https://www.britannica.com/topic/perception
https://www.britannica.com/topic/reason
https://www.britannica.com/biography/Plato
https://www.britannica.com/topic/Meno-by-Plato
https://www.britannica.com/biography/Socrates
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Plato’s successor Aristotle (384–322 BCE) conceived of the work of reason in the same way, 

though he did not view the forms as independent. His chief contribution to rationalism lay in 

his syllogistic logic, regarded as the chief instrument of rational explanation. Humans explain 

particular facts by bringing them under general principles. Why does one think Socrates will die? 

Because he is human, and humans are mortal. Why should one accept the general principle itself 

that all humans are mortal? In experience such principles have so far held without exception. But 

the mind cannot finally rest on this sort of explanation. Humans never wholly understand a fact 

or event until they can bring it under a principle that is self-evident and necessary; they then have 

the clearest explanation possible. On this central thesis of rationalism, the three great Greeks 

were in accord. Nothing comparable in importance to their thought appeared in 

rationalistic philosophy in the next 1,800 years, though the work of St. Thomas Aquinas (c. 

1225–74) was an impressive attempt to blend Greek rationalism and Christian revelation into a 

single harmonious system. 

 

15.3.2 Epistemological Rationalism in Modern Philosophies 

 

The first modern rationalist was Descartes, an original mathematician whose ambition was to 

introduce into philosophy the rigour and clearness that delighted him in mathematics. He set out 

to doubt everything in the hope of arriving in the end at something indubitable. This he reached 

in his famous cogito ergo sum, “I think, therefore I am”; for to doubt one’s own doubting would 

be absurd. Here then was a fact of absolute certainty, rendered such by the clearness and 

distinctness with which it presented itself to his reason. His task was to build on this as a 

foundation, to deduce from it a series of other propositions, each following with the same self-

evidence. He hoped thus to produce a philosophical system on which people could agree as 

completely as they do on the geometry of Euclid. The main cause of error, he held, lay in the 

impulsive desire to believe before the mind is clear. The clearness and distinctness upon which 

he insisted was not that of perception but of conception, the clearness with which the intellect 

grasps an abstract idea, such as the number three or its being greater than two. 

 

His method was adopted in essentials by both Benedict Spinoza (1632–77) and G.W. 

Leibniz (1646–1716), who agreed that the framework of things could be known by a priori 

thinking. They differed from him, however, in their starting points. What was most undeniable to 

Spinoza was not the existence of his self but that of the universe, called by him “substance.” 

From the idea of substance, and with the aid of a few definitions and axioms, he derived his 

entire system, which he set forth in his Ethics in a formal fashion patterned after Euclid’s 

geometry. Still, for both Spinoza and Leibniz much in nature remained stubbornly opaque. 

Leibniz distinguished necessary truths, those of which the opposite is impossible (as in 

mathematics), from contingent truths, the opposite of which is possible, such as “snow is white.” 

But was this an ultimate distinction? At times Leibniz said boldly that if only humans knew 

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enough, they would see that every true proposition was necessarily true—that there are no 

contingent truths, that snow must be white. 

 

How, then, does reason operate and how is it possible to have knowledge that goes beyond 

experience? A new answer was given by Immanuel Kant in his Critique of Pure Reason (1781; 

1787), which, as he said, involved a Copernican revolution in philosophy. The reason 

that logic and mathematics will remain valid for all experience is simply that their framework 

lies within the human mind; they are forms of arrangement imposed from within upon the raw 

materials of sensation. Humans will always find things arranged in certain patterns because it is 

they who have unwittingly so arranged them. Kant held, however, that these certainties were 

bought at a heavy price. Just because a priori insights are a reflection of the mind, they cannot be 

trusted as a reflection of the world outside the mind. Whether the rational order in which 

sensation is arranged—the order, for example, of time, space, and causality—represents an order 

holding among things-in-themselves (German Dinge-an-sich) which cannot be known. Kant’s 

rationalism was thus the counterpart of a profound skepticism. 

G.W.F. Hegel (1770–1831), the most thoroughgoing of rationalist thinkers, attempted to break 

out of this skepticism. He argued that to think of an unknowable is already to bring it within the 

sphere of what is known and that it is meaningless to talk of a region in which logic is invalid. 

Further, to raise the question “Why?” is to presume that there is an intelligible answer to it; 

indeed, the faith of the philosopher must be that the real is the rational and the rational real, for 

this faith is implicit in the philosophical enterprise itself. As an attempt to understand and explain 

the world, philosophy is a process of placing something in a context that reveals it as necessary. 

But this necessity is not, as earlier rationalists had supposed, an all-or-nothing affair issuing in a 

self-evident finality. Understanding is a matter of degree. What alone would wholly satisfy 

thought is a system that is at once all-inclusive and so ordered that its parts entail each other. 

Hegel believed that the universe constitutes such a whole and, as an idealist, held that it is a 

single, absolute mind. To the degree that philosophers embody and realize this mind, their own 

minds will achieve both truth and reality. Indeed, the advance of civilization reflects the 

enlarging presence and control of such a system in the human spirit. Broadly similar rationalistic 

systems were developed in England by F.H. Bradley (1846–1924) and Bernard 

Bosanquet (1848–1923) and in America by Josiah Royce (1855–1916). However, we shall 

consider the works of these major rationalists 

Major Proponents of Rationalism 

While the roots of Rationalism may go back to the Eleatics and Pythagoreans of ancient Greece, 

or at least to Socrates, Plato, Aristotle and the Neo-Platonists, the definitive formulation of the 

theory had to wait until the seventeenth Century philosophers of the Age of Reason. 

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René Descartes is one of the earliest and best known proponents of Rationalism. He believed that 

knowledge of eternal truths (e.g. mathematics and the epistemological and metaphysical 

foundations of the sciences) could be attained by reason alone, without the need for any sensory 

experience. Other knowledge (such as the knowledge of physics) required experience of the 

world, aided by the scientific method - a moderate rationalist position. For instance, his famous 

dictum “Cogito ergo sum” (I think, therefore I am) is a conclusion reached apriori and not 

through an inference from experience. Descartes held that some ideas (innate ideas) come 

from God; other ideas are derived from sensory experience; and still others are fictitious (created 

by the imagination). Of these, the only ideas which are certainly valid, according to Descartes, are 

those which are innate. 

Baruch Spinoza expanded upon Descartes’ basic principles of Rationalism. His philosophy 

centered on several principles, most of which relied on his notion that God is the only absolute 

substance (similar to Descartes' conception of God), and that substance is composed of two 

attributes, thought and extension. He believed that all aspects of the natural world (including 

Man) were modes of the eternal substance of God, and can therefore only be known through pure 

thought or reason. 

Gottfried Leibniz attempted to rectify what he saw as some of the problems that were not settled 

by Descartes. This he did by combining Descartes' work with Aristotle's notion of form and his 

own conception of the universe as composed of monads. He believed that ideas exist in 

the intellect innately, but only in a virtual sense, and it is only when the mind reflects on itself that 

those ideas are actualized. 

Immanuel Kant started as a traditional rationalist, having studied Leibniz and Christian 

Wolff (1679 - 1754). After studying the empiricist David Hume’s works, he developed a 

distinctive and very influential Rationalism of his own, which attempted to synthesize the 

traditional rationalist and empiricist traditions. 

Descartes 

The advent of the Age of Science, mathematical sciences such as arithmetic, geometry etc., 

alongside the Renaissance came with a new outlook of the world, which involved a paradigm 

shift from the previous foundations of Philosophy and academic discourse in general. 

Philosophers struggled to get rid of its footings on Scholasticism and Aristotelian foundation. 

History records the wave of thought at the beginning of this age as ‘Continental Rationalism’ 

which was pioneered by René Descartes and later propagated by Baruch Spinoza and Gottfried 

Leibnitz. They maintain that genuine knowledge has its foundation in thought or reason. 

According to them, the mind is full of rational content, inborn ideas, and innate principles. 

Dethronement of Traditional Philosophy 

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René Descartes (1596-1650) often known in Latin as Renatus Cartesius, born in the town of La 

Haye in Touraine, Brittany, France, studied Logic, Mathematics and Philosophy at the renowned 

Jesuit college of Le Fleche. His major works include;Discourse on Method (1637), Meditations 

on First Philosophy (1641) and Principles of Philosophy (1644).Descartes was chiefly concerned 

with the problem of intellectual certainty.Unsatisfied by the methods of his predecessors and 

pressured by the urge to break away from a ‘Philosophy’ having its roots in uncertainties, 

dogmas, and hearsays, René Descartes by means of the certitude of mathematics and influenced 

by the sciences of his time, sought to establish a rational foundation for his philosophy which 

would be so certain in an unassailable manner.He insists that “nothing solid could have been 

built upon such shaky foundations”342 (the foundations of past philosophies and false 

doctrines).Impressed by the exactness of Mathematics, he believed that the basis for his own 

philosophy would be a truth apprehended by the mind alone which would be self-evident and 

reliable like the mathematical theorems. He says, “I resolved one day to undertake studies within 

myself too and to use all the powers of my mind in choosing the paths I should follow.”343 

Enthronement of the Cartesian Methods 

Descartes did not find the traditional Aristotelian style of Logic appealing and leading to 

indubitable. For him, Aristotle’s deductive logic (syllogism) does not lead to the discovery of 

any new facts. Rather, it draws inferences from one already existing fact to the other. Against 

this unreliable system, Descartes enthrones his own methods of intuition and deduction as the 

only two guaranteed ways of arriving at indubitable truth(s).For Descartes, intuition is the 

conception which an unclouded and attentive mind gives us so readily and distinctly that we are 

wholly freed from doubt about that which we understand which springs from the light of reason 

alone. Deduction on the other hand follows from what is given us in intuition and also leads us to 

an indubitable truth. According to Descartes, deduction is that by which we understand al 

necessary inference of other facts that are known with certainty. The first principles are given 

alone by intuition while the remote conclusions are foregrounded by deduction. 

Descartes’ Methodological Skepticism 

Descartes was of the idea that before imploring the light of reason to acquire intuitive truths, he 

needs to exhume himself of all previously held beliefs. He points out that our firm opinions and 

beliefs originate from the senses and since these capacities (senses of perception) are deceptive, 

because the perceptions gotten through them are inconsistent, vague, illusive, and therefore 

cannot to be trusted. To begin with, Descartes suggests that one needs to primarily investigate 

the foundations on which all previously held opinions depend, on account of their dubitability. 

This must be done cautiously for even the highly undoubtful and improbable of our beliefs could 

appear false.  Firstly, doubt has to be the starting point for his search of certainty. Secondly, 

‘all’previous beliefs must be subject to doubt provided they can be doubted. Thirdly, that which 

                                                             
342René Descartes,Discourse on the Method, trans. John Cottingham, Robert Stoothoff, and Dugald Murdoch, in 
The Philosophical Writings of Descartes, vol. 1 (Cambridge, England: Cambridge University Press, 1985), 1.9, 115. 
343Ibid.,1.10, 116. 



151 
 

is doubted must be considered false until proven indubitable. However, in doubting these sorts of 

beliefs, Descartes is not asserting extreme skepticism. His position is more properly labeled as 

“methodological skepticism” for he uses the skeptical stance as a tool or method for testing his 

beliefs; hence the name, Methodic Doubt. 

Cogito Ergo Sum- Descartes’ Archimedean Point 

Descartes earlier stated that in his rigorous search for a solid foundation for philosophy, he had 

to discard all erroneous beliefs. He then notes that if he could find just one thing, however slight, 

that is certain and unshakable, that would be sufficient to counter his doubts and establish a 

philosophy. He continued in his system of methodic doubt until a point where he recognized that 

he could no longer doubt the fact that he was doubting. Like Augustine’s theory of Divine 

illumination, the light of reason shown upon Descartes at this point revealing to him that the fact 

that he was doubting implied that he was thinking, and to think, implied that he exists. Thus, he 

exclaimed cogito ergo sum- I think, therefore I exist. It is the internal condition of the act of 

doubting which escapes doubt. Hence, this implies that the metaphysical doubt of the existence 

of the thinking subject is rendered absurd by the awareness of the act of its doubting itself. 

Considered to be a truth so clear, distinct, and certain to the mind, Descartes established the 

cogito as his sure foundation on which he sets to build his entire philosophical thoughts. 

Other Deductive Truths 

Using the cogito as his standing point for philosophical reflections and meditations, Descartes set 

out to prove how he could arrive at other indubitable truths by means of deduction. He presented 

the cogito as a self-evident truth arrived at by means of intuition. He further deduces the 

existence of God from this proposition. His argument can simply be arranged in the following 

manner: 

 I know that I exist, and that I have an idea of an infinite perfect Being (God). 

 This idea of an infinite perfect Being cannot be created by a finite imperfect being 

 I am a finite imperfect being and therefore not the cause of this infinite perfect idea. 

 There necessarily exists an infinite perfect being that created this infinite perfect idea. 

 This infinite perfect being is God and he necessarily exists. 

This follows the ontological argument style of St. Anselm used in proving God’s existence. 

Though this argument has being flawed from various thinkers, Descartes believes that the proof 

of God’s existence is also an indubitable truth deduced from the proof of his very own 

existence- the cogito. 

Sources of Human Knowledge 

Descartes is considered as a renowned dualist for his conception of two major substances in the 

human person namely: res cogitans (thinking substance) and res extensa (extending substance). 

Where the former referred to the mind and all mental properties, the latter referred to the bodily 

organs which were responsible for sensory perception. He recognizes both the mind and senses 

as two distinct apparatuses that facilitated the acquiring of knowledge. Nevertheless, being at 



152 
 

the for-front of Rationalism, he denigrates knowledge gotten through the sense as unreliable and 

illusive. He holds the abstract truths apprehended by the mind through reason as the only 

reliable kind of knowledge. 

 

Spinoza 

Another continental rationalist worthy of note is Benedict Baruch Spinoza (1632-1677) a 

Portuguese Jew. He was highly influenced by René Descartes that the method of Geometry 

would give us true knowledge of reality. Thus, he attempted writing a geometry of Philosophy. 

His most prominent works include: Principles of Cartesian Philosophy (1663) Theologico-

Political Treatise (1670), and Ethics Demonstrated in Geometrical Order which contained a 

total of 259 demonstrated propositions. Continuing to follow Euclid’s style, Spinoza through his 

250 axioms attempted to explain the whole of reality in a systematic arrangement of true ideas. 

As conclusions are demonstrated in geometry, Spinoza believed that the theories of nature could 

also be demonstrated. He thus retorted that our rational powers could form ideas that reflect the 

true nature of things. For him, every clear and distinct idea or definition is “true.” In other words, 

every true idea gives a true picture of reality because the order and connection of ideas is the 

same as the order and connection of things in reality. 

The Idea of God 

Where Descartes began his philosophy with the cogito- a clear and distinct conception of his 

very own existence, Spinoza speculated that every rational enterprise that seeks to be free from 

all forms of error must first begin with the formulation of the ‘idea of God’. For him, God is 

prior to everything else. To know something is to know the cause and God is the first cause. All 

that happens to exist develop their being in God and thus, no idea can be conceived without God.  

According to Spinoza, God is a being absolutely infinite. All elements of reality/nature only 

reflect some of the infinite attributes of this Eternal Being. Reality is therefore One- God, which 

manifests in all individuating substances. By so doing, where Descartes could be said to be a 

Dualist, Spinoza was basically a Monist for he believed the whole of reality is a Unity. 

The Types of Ideas 

Spinoza theorized that an idea is nothing else outside rational sensation. Notwithstanding, only 

the rational powers of the mind could lead man to the formulation of ideas that reflect the exact 

nature of objects i.e., the essences of things. For him, every clear and distinct idea is true and 

accurately reflects the ideal picture of reality. In other words, to know a thing is to know its 

essence. He further distinguished between three major types of ideas: 

True Idea: this refers to a simple idea i.e., an idea that is clear, distinct and self-evident. For 

example, the idea of God. 

False Idea: this refers to a perception clouded in confusion. It is not clear, distinct or self-

evident. It is inadequate and does not affirm of a thing what is contained in its form. 

Doubt: this arises when an idea is not clear and distinct enough for us to be able to draw any 

conclusion with regards its true nature or essence. 

The Four Levels of Knowledge 



153 
 

a. Hearsay: this refers to a kind of knowledge which is uncertain. As the name suggests, we 

come to acquire such knowledge by gossip or the narration of someone else even without 

firsthand experience. E.g. knowledge of one’s birth date. 

b. Imagination/ Mere Experience: this refers to ideas that are confusing, inadequate, and 

lead only to falsity. We come to acquire such knowledge by means of our sense perceptions. 

Yes, they directly affect the senses but they remain unclear and uncertain. For they do not reveal 

the essences of things. Though these ideas from sensory things are useful for our daily life, they 

do not give any true knowledge. E.g. knowledge of the inevitability of death based on one’s 

experience of the death of others. 

c. Reason: this kind of knowledge involves logical deduction. It is a scientific knowledge 

which involves common notions and adequate ideas of the properties things. Here, the essence of 

things are inferred from others when we gather resultant effects from their direct causes. In this 

exercise, the mind rises above immediate and particular things and deal with abstract ideas as it 

does in the mathematical sciences. Knowledge at this level is considered adequate and true. 

d. Intuition: this is the highest degree of knowledge. It involves mathematical truths and 

first principles or axioms i.e., truths that their denial lead to a self contradiction. For Spinoza, an 

intuitive knowledge proceeds from an adequate idea of former essence of certain attributes of 

God to the adequate knowledge of the essence of things. It is the ONLY secure and reliable 

knowledge for it apprehends the adequate essence of thing without error. It enables us to see 

things in themselves and in their relations with others. By so doing, we are able to grasp the 

whole system of nature. 

 

Leibniz 

Gottfried Wilhelm Leibniz (1646-1716) is the third great continental rationalist philosopher born 

in Leipzig, Germany. Four successive schools of philosophy which influenced his education 

were; Scholasticism, Materialism, Cartesianism, and Spinozism. He later emancipated from these 

schools and got involved into the ‘mathematical materialism’ of the day. This accounts for his 

founding of Binary Mathematics, and Infinitesimal Calculus. Besides Leibnitz academic interest, 

he was a religious man, a Christian. He wrote extensively in the area of philosophy, of which his 

main works include the Monadology, New Essay in Human Understanding, Essays in Theodicy, 

New System of Nature and the Interaction of Substances.  

Leibnitz in his philosophy was occupied with the task of the search for unity and harmony of the 

whole of reality/universe. Like Galileo, he believed the universe is a harmonious system written 

in mathematical language by God. This led him to the realisation that basic ideas, like those 

found in Logic and Mathematics could not be derived by the senses for they are eternal truths. 

He is essentially a pluralist which is reflected in his metaphysical idea of monads (Monadology) 

which says that things in nature are a composite/aggregate of simple substances. This would lead 

him later on to his Epistemology properly. 

Theory of Monads 



154 
 

Leibniz discovered that things found in nature are made up of monads. They are basic substances 

that make up the universe. He states that these monads can be conceived as unextended, 

immaterial, invisible, indivisible atom-like substances having no quantity, size or shape. Each 

monad is unique constituting small units of basic elements with which all in the universe is 

made. Each monad is thus self-contained and windowless i.e., they are independent without any 

causal relationship with another. They all mirror the universe clearly and distinctively by means 

of perception. 

Monadology and Human Knowledge 

Having established that monads are windowless having no causal relationship, Leibniz states that 

one monad always dominates in every collective group of monads. In man, the dominating 

monad is the human mind. He believes that ideas (monads) are stored up in the mind (the 

dominating monad) since ideas are simply expressions of the soul i.e., a mirroring or reflection 

of the mind which is itself a monad. Thus, ideas are in us and are always there whether we think 

of them or not. Ideas are innate. Our mind, a monad, expresses all essences as well as existences. 

This goes on to imply that we do not gain any knowledge from the sensory world. All that we 

know and need to know throughout our existence has been stored up in the mind before birth. 

The mind being windowless does not allow for any entering of a new knowledge. Our ideas do 

not come from external senses but inner experience. It is thus for Leibnitz, largely misleading, to 

conceive of the mind as a receptor of new knowledge for nothing can be taught us of which we 

have not already in our minds. The most which happens to us is a revitalization of latent 

knowledge in the mind by means of sense perceptions. 

Degrees of Knowledge 

On first apprehension, Leibniz posits that knowledge is either clear or obscure. A clear 

knowledge is one able to be recognized when presented us as against the latter. Clear knowledge 

is either distinct or confused. The former is one whose marks can be distinctly separated from 

another while the properties of the latter cannot be differentiated even though it is recognized. 

Distinct knowledge is either adequate or inadequate. An adequate knowledge is that which all its 

marks/properties are themselves distinctly known while those of the latter are not distinctly 

known. Adequate knowledge is either intuitive or symbolic. Intuitive knowledge is a notion 

which the mind understands distinctly and grasps at the same time all its simple ingredients. 

Symbolic knowledge occurs when we are unable to contemplate all elements of a complex idea 

but replace it with signs. For Leibniz, the bulk of human knowledge is only confused or symbolic 

knowledge. The purest and surest of all degrees of knowledge is the Intuitive Knowledge but is 

very rare in our daily conceptions.Perfect knowledge for Leibnitz is both adequate and intuitive. 

In his words, “I have defined idea adeœquata (a perfect idea) as that which is so distinct that all 

its ingredients are distinct, and such is nearly the idea of a number.”344 

Necessity and Contingency 

                                                             
344 G. W. Leibniz, New Essays on the Human Understanding Book II CH. XXXI,trans. Alfred Gideon Langley 

(New York: The Macmillan Company, 1896), 278. 



155 
 

 Leibniz while analysing his view of innate ideas made a distinction between necessity 

and contingency. A necessary proposition is a proposition that states truth of reason and is 

analytic, as distinct from a contingent proposition which states truth of fact and is synthetic. For 

Leibniz, truths of reason are necessary and their contradictory is impossible, while truths of fact 

are contingent and their contradictory is possible. Where propositions of Mathematics are 

necessary, those asserting particular existence are contingent. For Leibniz, the necessary is not 

same as the à priori. 

Truth of Reason and Truth of Fact 

Truth is said to be the correspondence of a proposition with reality, which may be either actual or 

possible. These propositions show two kinds of truth which are; truth of reason and truth of fact. 

According to Leibniz, the law of contradiction is the sole ultimate premise of all truth of reason, 

while truth of facts, have as many ultimate premises as there are experiences— they rest on the 

principle of sufficient reason. This accounts for Leibniz’s distinction of knowledge gained by 

perception, and knowledge gained by reasoning. Classical examples of truths of reason are; two 

parallel lines never intersect each other, a circle is two semi-circles, an angle of 40 degrees is an 

acute angle, an axiom is self-evidently true etc. These examples reveal truths of reason which are 

necessary propositions that are independent of external causes for their existence. Their 

contradictory is impossible, and they are analytic in nature. At best, they can be referred to as 

tautologies. Examples of truths of facts are; the snow is white, Socrates is a married man, Marcel 

is teaching etc. These are not necessary propositions, but they are contingent. When we deny 

them, there will be no logical contradiction. Thus, their contradictory is possible.  They are 

dependent on external causes for their existence and are synthetic in nature.   

Basic Principles in Leibniz’s Analysis of Truth 

The two basic principles in Leibniz’s analysis of truth are; the principle of contradiction and the 

principle of sufficient reason. These principles are based on Leibniz’s concept of innate ideas in 

acquiring true knowledge. The principle of contradiction (which is also called the principle of 

identity) states that all necessary (analytic) propositions are true, while the principle of sufficient 

reason states that contingent propositions may either be true or false, hence, they can only be 

truth if there is sufficient reason to prove them. When we make existential statements, we have to 

give sufficient reason to say that they are true. According to Leibniz, all propositions about 

existence of something are contingent. This is because they state truth of fact. However, Leibniz 

gave an exception to that of “the existence of God.” He says that the proposition on the existence 

of God is in itself an embodiment of truth of reason which is a necessary, thus, when it is denied; 

it would result to a logical contradiction because the very concept of God implies his existence. 

 

15.4 Types of Rationalism 

 

15.4.1 Ethical Rationalism 

 



156 
 

The views of Kant were presented above as typical of this position. But few moralists have held 

to ethical rationalism in this simple and sweeping form. Many have held, however, that the main 

rules of conduct are truths as self-evident as those of logic or mathematics. Lists of such rules 

were drawn up by Ralph Cudworth (1617–88) and Henry More (1614–87) among the Cambridge 

Platonists, who were noted for holding that moral principles were intrinsic to reality; 

later Samuel Clarke (1675–1729) and Richard Price (1723–91), defenders of “natural 

law” ethics, and the “common sense” moralist Thomas Reid (1710–96) also presented such lists. 

A 20th-century revision of this rationalism was offered by the intuitionists H.A. Prichard (1871–

1947) and Sir David Ross (1877–1971) of Oxford under the name of deontology (from the 

Greek deon, “duty”), which respects duty more than consequences. Ross provides a list of 

propositions regarding fidelity to promises, reparation for injuries, and other duties, of which he 

says: “In our confidence that these propositions are true there is involved the same trust in our 

reason that is involved in our trust in mathematics.” What is taken as self-evident, however, is 

not specific rules of conduct but prima facie duties—the claims that some types of action have on 

humans because of their nature. If a person is considering whether to repay a debt or to give the 

money to charity, each act has a self-evident claim on that person, and their comparative 

strengths must be settled by a rational intuition. 

 

The most-influential variety of 20th-century ethical rationalism was probably the 

ideal utilitarianism of the British moralists Hastings Rashdall (1858–1924) and G.E. 

Moore (1873–1958). Both were teleologists (from the Greek telos, “end”) inasmuch as they held 

that what makes an act objectively right is its results (or end) in intrinsic goods or evils. To 

determine what is right, reason is required in two senses: first, the inference to the consequences 

is an act of inductive reasoning; second, the judgment that one consequence is intrinsically better 

than another is a priori and self-evident. Moore thought that there is a single rule for all 

conduct—one should so act as to produce the greatest good—and that this is also a principle self-

evident to reason. 

 

15.4.2 Religious Rationalism 

 

Stirrings of religious rationalism were already felt in the Middle Ages regarding the 

Christian revelation. Thus, the skeptical mind of Peter Abelard (1079–1142) raised doubts by 

showing in his Sic et non (“Yes and No”) many contradictions among beliefs handed down as 

revealed truths by the Church Fathers. Aquinas, the greatest of the medieval thinkers, was a 

rationalist in the sense of believing that the larger part of revealed truth was intelligible to and 

demonstrable by reason, though he thought that a number of dogmas opaque to reason must be 

accepted on authority alone. 

 

15.4.2.1 Expansion of Religious Rationalism 

 

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Religious rationalism did not come into its own, however, until the 16th and 17th centuries, 

when it took two chief forms: the scientific and the philosophical. 

Galileo was a pioneer in astronomy and the founder of modern dynamics. He conceived of nature 

as governed throughout by laws statable with mathematical precision; the book of nature, he 

said, is “written in mathematical form.” This notion not only ruled out the occasional appeal 

to miracle; it also collided with dogmas regarding the permanent structure of the world—in 

particular with that which viewed the Earth as the motionless centre of the universe. When 

Galileo’s demonstration that the Earth moves around the Sun was confirmed by the work of 

Sir Isaac Newton (1642–1727) and others, a battle was won that marked a turning point in the 

history of rationalism, since it provided a decisive victory in a crucial case of conflict between 

reason and apparently revealed truth. 

The rationalism of Descartes, as already shown, was the outcome of philosophical doubt rather 

than of scientific inquiry. The self-evidence of the cogito, seen by his “natural light,” he made 

the ideal for all other knowledge. The uneasiness that the church soon felt in the face of such a 

test was not unfounded, for Descartes was in effect exalting the natural light into the supreme 

court even in the field of religion. He argued that the guarantee against the possibility that even 

this natural light might be deceptive lay in the goodness of the Creator. But then to prove this 

Creator, he had to assume the prior validity of the natural light itself. Logically, therefore, the 

last word lay with rational insight, not with any outside divine warrant (see Cartesian 

circle). Descartes was inadvertently beginning a Copernican revolution in theology. Before his 

time, the truths regarded as most certain were those accepted from revelation; afterward these 

truths were subject to the judgment of human reason, thus breaking the hold of authority on the 

European mind. 

 

15.4.2.2 Four Waves of Religious Rationalism 

 

The rationalist attitude quickly spread, its advance forming several waves of general interest and 

influence. The first wave occurred in England in the form of Deism. Deists accepted 

the existence of God but spurned supernatural revelation. The earliest member of this 

school, Lord Herbert of Cherbury (1583–1648), held that a just God would not reveal himself to 

a part of his creation only and that the true religion is thus a universal one, which achieves its 

knowledge of God through common reason. The Deistic philosopher John Toland (1670–1722), 

in his Christianity Not Mysterious (1696), sought to show that “there is nothing in the Gospels 

contrary to reason, nor above it”; any doctrine that is really above reason would be meaningless 

to humans. Attacking revelation, the freethinking polemicist Anthony Collins (1676–1729) 

maintained that the prophecies of the Hebrew Bible (Old Testament) failed of fulfillment; and 

the religious controversialist Thomas Woolston (1670–1733) urged that the New 

Testament miracles, as recorded, are incredible. Matthew Tindal (1657–1733), the most learned 

of the English Deists, argued that the essential part of Christianity is its ethics, which, being 

clearly apparent to natural reason, leaves revelation superfluous. Thus the Deists, professing for 

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the most part to be religious themselves, did much to reconcile their public to the free play of 

ideas in religion. 

 

The second wave of religious rationalism, less moderate in tone and consequences, was French.  

This wave, reflecting an engagement with the problem of natural evil, involved a decay in the 

natural theology of Deism such that it merged eventually with the stream that led to 

materialistic atheism. Its moving spirit was Voltaire (1694–1778), who had been impressed by 

some of the Deists during a stay in England. Like them, he thought that a rational person would 

believe in God but not in supernatural inspiration. Hardly a profound philosopher, he was a 

brilliant journalist, clever and humorous in argument, devastating in satire, and warm in human 

sympathies. In his Candide and in many other writings, he poured irreverent ridicule on the 

Christian scheme of salvation as incoherent and on the church hierarchy as cruel and oppressive. 

In these attitudes he had the support of Denis Diderot (1713–84), editor of the most widely read 

encyclopaedia that had appeared in Europe. The rationalism of these thinkers and their followers, 

directed against both the religious and the political traditions of their time, did much to prepare 

the ground for the explosive French Revolution. 

 

The next wave of religious rationalism occurred in Germany under the influence of Hegel, who 

held that a religious creed is a halfway house on the road to a mature philosophy, the product of a 

reason that is still under the sway of feeling and imagination. This idea was taken up and applied 

with learning and acuteness to the origins of Christianity by David Friedrich Strauss (1808–74), 

who published in 1835, at the age of 27, a remarkable and influential three-volume work, Das 

Leben Jesu (The Life of Jesus, Critically Examined, 1846). Relying largely on internal 

inconsistencies in the Synoptic Gospels, Strauss undertook to prove these books to be 

unacceptable as revelation and unsatisfactory as history. He then sought to show how an 

imaginative people innocent of either history or science, convinced that a messiah would appear, 

and deeply moved by a unique moral genius, inevitably wove myths about his birth and death, 

his miracles, and his divine communings. 

Strauss’s thought as it affected religion was continued by the philosophical historian Ernest 

Renan (1823–92) and as it affected philosophy by the humanist Ludwig Feuerbach (1804–72) of 

the Hegelian left. Renan’s Vie de Jésus (1863; Life of Jesus) did for France what Strauss’s book 

had done for Germany, though the two differed greatly in character. Whereas Strauss’s work had 

been an intellectual exercise in destructive criticism, Renan’s was an attempt to reconstruct the 

mind of Jesus as a wholly human person—a feat of imagination, performed with a disarming 

admiration and even reverence for its subject and with a felicity of style that gave it a large and 

lasting audience. Feuerbach’s Wesen des Christentums (1841; Essence of Christianity) applied 

the myth theory even to belief in the existence of God, holding that “man makes God in his own 

image.” 

The fourth wave occurred in Victorian England, following the publication in 1859 of Origin of 

Species by Charles Darwin (1809–82). This book was taken as a challenge to the authority 

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of Scripture because there was a clear inconsistency between the Genesis account of creation and 

the biological account of humans’ slow emergence from lower forms of life. The battle raged 

with bitterness for several decades but died away as the theory of evolution gained more general 

acceptance. 

 

15.5 Status of Rationalism 

 

15.5.1 Religious 

 

With increasing freedom of thought and wider acceptance of scientific views, rationalism in 

religion lost its novelty and much of its controversial excitement. To the contemporary mind, it is 

too obvious to warrant debate that reason and revelation cannot both qualify as sources of 

ultimate truth, for, were they to conflict, truth itself would become self-contradictory. Hence 

theologians sought accommodation through new interpretative principles that discern different 

grades of authenticity within the Scriptures and through new views of religious 

truth, existential rather than cognitive that turn from propositional dogmas to the explication of 

lived human existence. Criticism of supernaturalism, however, was still carried on by such 

societies as the Rationalist Press Association, in Great Britain, and the Humanist Association, in 

the United States. 

 

15.5.2 Ethical 

 

Rationalism in ethics suffered its share of criticism. Regarding its lists of rules—on the keeping 

of promises, the return of loaned goods, etc.—it was argued, for example, that if they were 

specific enough to be useful (as in the rule against lying or stealing), they would tend to have 

exceptions—which no rule laid down by reason ought to have. On the other hand, if without 

exceptions, they would often prove to be tautologies: the rule of justice, for example, that one 

should give all persons their due, would then mean only that one should give them what is justly 

theirs. After enduring a period of eclipse, however, during which noncognitive theories of ethics 

(emotive and existential) and relativism had preempted the field, rationalistic views, which agree 

in holding that moral standards do not depend upon the varying attitudes of persons or peoples, 

received renewed attention in the mid-twentieth century. Prominent among these developments 

was the “good-reasons” approach taken by the broadly gauged scholar Stephen Toulmin (1922–

2009), the contemporary philosopher Kurt Baier, and others, which examined the contexts of 

various moral situations and explored the kinds of justification appropriate for each. 

 

15.5.3 Metaphysical 

 

Typical of the ways of reasoning employed by rationalists were two approaches taken to 

the metaphysical doctrine that all things are connected by internal relations: one a logical, the 

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other a causal argument. An internal relation is one that could not be removed without affecting 

the terms themselves between which the relation holds. The logical argument runs: Everything is 

related to everything else at least by the relation “A is different from B.” But difference is itself 

an internal relation, since the terms could not remain the same if it were removed. Hence 

everything is so connected with everything else that it could not be what it is unless they were 

what they are. The appeal to internal relations played an important part in the philosophies of 

Hegel, F.H. Bradley, and A.N. Whitehead (1861–1947). 

The other line of argument is causal. Every event, it is maintained, is connected with every other, 

either directly or indirectly. Sir James Jeans (1877–1946), an astrophysicist and popularizer of 

science, argued that if the law of gravitation is valid, people cannot crook their little fingers 

without affecting the fixed stars. Here the causal relation is direct. It can also be shown that 

seemingly unrelated events are joined indirectly through their common connection with some 

remote historical event, by a chain of events leading back, for example, to Columbus’s landing 

on the North American continent. But if this had been different, all its consequences would 

presumably have been different; thus, an indirect and internal relation proves to have been 

present. 

Many rationalists held with Spinoza that the causal relation is really a logical one—that a causal 

law, if precisely stated, would reveal a connection in which the character of the cause logically 

necessitates that of its effect; and if this is true, they maintained, the facts and events of the world 

must thus compose a single rational and intelligible order. 

In the twentieth century, such rationalism met with a new and unexpected difficulty presented 

by quantum mechanics. According to the indeterminacy principle, formulated in 1927 by the 

German physicist Werner Heisenberg (1901–76), it is impossible to discover with precision both 

the position and the velocity of a moving electron at the same time. This implies that definite 

causal laws for the behaviour of these particles can never be attained, but only statistical laws 

governing the behaviour of immense aggregates of them. Causality, and with it the possibility of 

rational understanding, seemed to be suspended in the subatomic world. Some interpreters of the 

new physics, however, notably Max Planck (1858–1947), Albert Einstein (1879–1955), 

and Bertrand Russell (1872–1970), sustained the hopes of the rationalists by insisting that what 

was excluded by the indeterminacy principle was not the fact of causality in this realm but only 

the precise knowledge of it. 

Indeed, some leaders of twentieth century science took the new developments in Physics as on 

the whole supporting rationalism. Protons and electrons, they contended, though beyond the 

reach of the senses, can still be known, and their behaviour, at least in groups, is increasingly 

found to conform to mathematical law. In 1932 Jeans said, with a curious echo of Galileo, “the 

universe appears to have been designed by a pure mathematician.” 

 

15.6 Challenges to Epistemological Rationalism 

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At first glance, the claim of empiricism that knowledge must come from sense experience seems 

obvious. How else could one hope to make contact with the world around one? However, 

rationalism has been sharply challenged—in the ninetieth century by the empiricism of John 

Stuart Mill (1806–73) and in the twentieth by that of the logical positivists, among other 

movements. Mill argued that all a priori certainties are illusory: Why do people believe, for 

example, that two straight lines cannot enclose a space? Is it because they see it as logically 

necessary? No, it is because they have experienced so long and so unbroken a row of instances of 

it—a new one whenever they see the corner of a table or the bordering rays of a light beam—that 

they have formed the habit of thinking in this way and are now unable to break it. A priori 

propositions, Mill claimed, are merely empirical statements of very high degree of generality. 

 

This theory has now been abandoned by most empiricists themselves. Its implication that such 

statements as “2 + 2 = 4” are only probably true and may have exceptions has proved quite 

unconvincing. The rationalists’ rejoinder is that one cannot, no matter how hard one tries, 

conceive 2 + 2 as making 5, for its equaling 4 is necessary. But a priori knowledge is also 

universal. Neither of these two characteristics can be accounted for by sense experience. That a 

crow is black can be perceived, but not that it must be black or that crows will always be black; 

no run of perceptions, however long, could assure us of such truths. On the other hand, a priori 

truths can be apprehended with certainty—that if a figure, for instance, is a plane triangle within 

a Euclidean space, its angles must and always will equal two right angles. 

 

One of the most formidable challenges to rationalism came in the twentieth century from such 

logical positivists as the Oxford empiricist A.J. Ayer (1910–89) and Rudolf Carnap (1891–

1970), who had been a central figure in the Vienna Circle, where this movement first arose. 

Unlike Mill, they accepted a priori knowledge as certain; but they laid down a new challenge—

the denial of its philosophical importance. A priori propositions, they said, are (1) linguistic, (2) 

conventional, and (3) analytic: They are linguistic statements being primarily of how one 

proposes to use words.  If one says for instance, that “a straight line is the shortest line between 

two points,” this merely reports one’s definition of “straight” and declares one’s purpose to use it 

only of the shortest. They are conventional given that as a definition, such statements express a 

convention to which there are alternatives the statement on straight may be defined in terms of 

the paths of light rays if one chooses. The statement is analytic in that it merely repeats in 

its predicate a part or the whole of the subject term and hence tells nothing new; it is not a 

statement about nature but about meanings only. And since rationalistic systems depend 

throughout upon statements of this kind, their importance is illusory. 

 

To this clear challenge some leading rationalists have replied as follows: (1) positivists have 

confused real with verbal definition. A verbal definition does indeed state what a word means; 

but a real definition states what an object is, and the thought of a straight line is the thought of an 

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162 
 

object, not of words. (2) The positivists have confused conventions in thought with conventions 

in language. One is free to vary the language in which a proposition is expressed but not the 

proposition itself. Start with the concept of a straight line, and there is no alternative to accepting 

it as the shortest. (3) Some a priori statements are admittedly analytic, but many are not. In 

“whatever is coloured is extended,” colour and extension are two different concepts of which the 

first entails the second but is not identical with it in whole or part. Contemporary rationalists 

therefore hold that the apriori has emerged victorious from the empiricists’ efforts to discredit 

such knowledge and the positivists’ attempts to trivialize it. 

15.7 Major Claims of Rationalism 

Rationalism is any view appealing to intellectual and deductive reason (as opposed to sensory 

experience or any religious teachings) as the source of knowledge or justification. Thus, it holds 

that some propositions are knowable by us by intuition alone, while others are knowable by 

being deduced through valid arguments from intuited propositions. Depending on the strength of 

the belief, this can result in a range of positions from the moderate view that reason 

has precedence over other ways of acquiring knowledge, to the radical position that reason is 

the only path to knowledge. 

Rationalism relies on the idea that reality has a rational structure in that all aspects of it can be 

grasped through mathematical and logical principles, and not simply through sensory experience. 

Rather than being a "tabula rasa" to be imprinted with sense data, the mind is structured by, and 

responds to, mathematical methods of reasoning. 

Rationalists adopt at least one of three main claims: 

Intuition/Deduction: Some propositions are knowable by us by intuition alone, while others are 

knowable by being deduced from intuited propositions. Some rationalists take intuition to 

be infallible, claiming that whatever we intuit must be true; others allow for the possibility 

of false intuited propositions. Some claim that only mathematics can be knowable by intuition and 

deduction; some that ethical truths can also be intuited; some more radical rationalists maintain 

that a whole range of metaphysical claims (like the existence of God, free will and the duality of 

mind and body) are included within the range of intuition and deduction. 

Innate Knowledge: We have knowledge of some truths as part of our innate rational nature. 

Experiences may trigger a process by which we bring this knowledge to consciousness, but the 

experiences do not provide us with the knowledge itself, which has in some way been with us all 

along. Some rationalists claim that we gained this innate knowledge in an earlier existence, some 

that God provided us with it at creation, and others that it is part of our nature through natural 

selection. 

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Innate Concepts: Some of the concepts (as opposed to actual knowledge) we employ are part of 

our innate rational nature. Some would argue, however, that innate concepts are entailed by innate 

knowledge, because a particular instance of knowledge can only be innate if the concepts that 

are contained in the proposition are also innate. 

Some rationalists also claim, in addition to the claims above, that the knowledge we gain by 

intuition and deduction, as well as the ideas and instances of knowledge that are innate to us, 

are indispensable and could not have been gained through sense experience, and/or that reason 

is superior to experience as a source of knowledge. 

15.8 Distinguishing Rationalism from Empiricism 

Rationalism is contrasted with Empiricism, the view that the origin of all knowledge is sense 

experience and sensory perception. It is usually associated with the introduction of mathematical 

methods into philosophy during the Age of Reason and the Enlightenment by the major rationalist 

figures, Descartes, Leibniz and Spinoza. It is commonly referred to as “Continental 

Rationalism” because it was predominant in the continental schools of Europe, whereas British 

Empiricism dominated in Britain. 

The distinction between Rationalism and Empiricism, however, is perhaps not as clear-cut as is 

sometimes suggested, and would probably not have even been recognized by the Enlightenment 

philosophers involved. For example, the three main rationalists were all committed to the 

importance of empirical science, and in many respects the empiricists were closer to Descartes in 

their methods and metaphysical theories than were Leibniz and Spinoza. 

Both Leibniz and Spinoza asserted that, in principle, all knowledge, including scientific 

knowledge, could be gained through the use of reason alone, though they both observed that this 

was not possible in practice for human beings, except in specific areas such as mathematics. 

 

 

 

 

 

 

 

 

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	Epistemology, as a distinct field of inquiry, predates the introduction of the term into the lexicon of philosophy. John Locke, for instance, described his efforts in Essay Concerning Human Understanding (1689) as an inquiry “into the original, certai...
	There are a number of different methods that contemporary scholars use when trying to understand the relationship between past epistemology and contemporary epistemology. One of the most contentious questions is this: Should we assume that the problem...
	1.2 What is Epistemology?
	4.2.1 No False Premises Response
	4.2.2 Reliabilist Response
	Reliabilism has been a significant line of response to the Gettier problem among philosophers, originating with work by Alvin Goldman in the 1960s. According to reliabilism, a belief is justified (or otherwise supported in such a way as to count towar...
	CHAPTER FIVE
	THE NATURE OF JUSTIFICATION
	5.1 Internalism and Externalism

	7.5 Why Foundationalism?
	SOURCES OF KNOWLEDGE AND JUSTIFICATION
	8.2 Perception
	8.3 Introspection
	8.4 Memory
	8.5 Reason
	8.6 Testimony
	9.5 Responses to the Closure Argument
	9.10 Responses to the Defeasibility Argument

	10.2.1 St. Anselm of Canterbury
	12.2.2.1 Absolute Empiricism
	14.5 Logical Empiricism


