Dermatology: Practical and Conceptual


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Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 11

Foreword
I decided to write this series of essays, “On the nature of 

thought processes and their relationship to the accumulation 

of knowledge” because it seems to me logical that if we do 

not understand the mechanisms that occur within our brains 

to generate thoughts (those thoughts underlying each and 

everything we do) we cannot begin to understand how or 

why events either occur according to plan or seem to go awry. 

The series looks at thought processes and the “knowledge” 

generated by them from a variety of perspectives. The goal is 

to better understand just how “true” items of knowledge are, 

or can be, and how that understanding might help us generate 

and communicate “knowledge” more accurately.

This current essay about the Nature of Evidence was 

originally published in Dermatopathology: Practical & Con-

ceptual in October 2009, but because of a series of unlucky 

events the essay has been withdrawn shortly after its publi-

cation without being ever replaced for the readership. After 

now 4 years, the essay will be finally again available for the 

readers of Dermatology Practical & Conceptual.

Further essays in the series are “in the works” and this 

essay is an important topic in the series overall, so I am 

pleased that it is to be republished.

Introduction
How do we decide what to believe? This question is most 

important for us because we each believe many things. Each 

of us assumes that what we believe is true, otherwise we 

would not believe it. And we are aware that we do not all 

believe all of the same things. If fact, we are convinced that 

many other people believe things which by definition they 

believe to be true, that are just plain wrong, or not true, 

because we do not believe those same things.

Of course we each have reasons for our beliefs. If someone 

asks us, “Why to you believe that?” we can respond, “Because. 

. . .” And we all believe that our reasons support adequately 

our decision to believe that item. So if all of my beliefs are 

true, and all of your beliefs are true, and all of our reasons 

collectively support our beliefs, why do we disagree so often?

Let us move on to the topic of this essay, the nature of 

evidence. The Random House Dictionary, second edition, 

defines “evidence” as “that which tends to prove or disprove 

something; ground for belief; proof” and “something that 

makes plain or clear.” Serving as it does as a justification for 

belief, evidence is something we simply cannot live without. 

The definition implies that evidence must be true and unas-

sailable, serving as a “ground for belief”, “belief” being 

something we assume to be true, and “proof”, which implies 

that there can be no argument. Also, the definition implies 

that evidence serves to clarify an issue, serving to improve 

our understanding of it. When we hear the “evidence” we are 

supposed to say “Aha! Now I understand” and we all move 

on to the next item of interest.

So the question arises, are “reasons for belief” the same 

as “evidence”? If we do consider them to be the same, should 

we consider them to be the same? In this essay we will look 

at the concept of evidence from a variety of perspectives and 

On the nature of thought processes and their 
relationship to the accumulation of knowledge, 

Part XIII: The nature of evidence
Cris Anderson1

1 Pathology, Southern Illinois University School of Medicine, Carbondale, Illinois, USA

Citation: Anderson C. On the nature of thought processes and their relationship to the accumulation of knowledge, Part XIII: The nature 
of evidence Dermatol Pract Concept. 2014;4(1):3. http://dx.doi.org/10.5826/dpc.0401a03

Copyright: ©2014 Anderson. This is an open-access article distributed under the terms of the Creative Commons Attribution License, 
which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Corresponding author: Cris Anderson, M.D., Email: crisj@me.com



12 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

try to gain some insight into the powerful hold the very word 

“evidence” holds over us. We will examine reasons why evi-

dence cannot be expected to be true and unassailable in each 

and every case. We will examine the question of whether or 

not the word “evidence” has become more of an instrument 

of persuasion than out-and-out “proof” and how this affects 

us in the day-to-day practice of medicine, which is supposed 

to be Evidence-Based.

Evidence—the ideal

Preston Cloud, in Oasis in Space: Earth History from the 

Beginning, states, “A subject becomes a science when it is 

brought within the bounds of natural law and a body of 

ordering principles that make its hypotheses testable—where 

evidence takes priority over authority and revelation.” This 

statement implies that evidence is more than merely some-

thing that “justifies belief.” It implies that the justification 

of belief must be a sort of “proof.” That is to say, a body of 

evidence—that body which can be evaluated independently 

by one or more persons other than the person who puts forth 

that body—should lead a reasonable person to conclude the 

belief on his or her own.

No doubt a person who accepts revelation as a reason 

for belief feels justified in believing what has come to him 

by means of revelation. Encarta World English Dictionary, 

first edition, defines “belief” as “acceptance by the mind that 

something is true or real, often underpinned by an emotional 

or spiritual sense of certainty.” That dictionary also defines 

“justify” as “to serve as an acceptable reason or excuse for 

something.” Thus, using the term “evidence” as “that which 

justifies belief” does not necessarily imply “proof.” Encarta 

defines “proof” as “evidence or an argument that serves to 

establish conclusively a fact or the truth of something.” How-

ever, I would argue that most of us infer “proof” when we hear 

the label “evidence” applied to some information given to us.

In a similar vein, returning to Cloud’s statement about sci-

ence, “authority”, if we accept it as a reason to believe some 

item of information, it serves to justify our acceptance of that 

item and becomes “evidence.”

In fact, “evidence” is not unique to science at all. What 

really makes science “science” is the “body of ordering prin-

ciples that make its hypotheses testable” and the actual testing 

of those hypotheses. The “evidence” that we scientists use 

does require “proof.” We try to use “proof” formally in the 

sense of deductive logic or mathematical proof, in which each 

ensuing step is agreed upon by all as following its predecessor.

Evidence in practice

We tend to use the term “evidence” rather freely, applying 

the term to a reason that we accept as justifying our belief, 

but without “thoroughly vetting” the term each time we use 

it to see if a rational person would accept necessarily our 

argument in the case at hand. We may do this without malice 

aforethought, being somewhat confused at the time as to our 

own argument; but occasionally a person might purposefully 

apply the term “evidence” in an attempt to prevent the audi-

ence from working through the argument themselves to see 

if the argument is actually a valid one. Unfortunately, often 

there is no easy way to tell whether the arguer is being logical, 

is confused, or is trying to hoodwink the audience.

Many problems exist in this complex world in which we 

live for which legitimate disagreements occur. For some of 

the reasons to be discussed later in this essay, a formal, unde-

niable proof cannot be put forth. This does not mean that 

there are no rules available with which such a problem can 

be discussed in a meaningful and enlightening way.

In fact, informal logic, or argumentation, is a discipline 

which recognizes that “proof” more often than not represents 

a consensus arrived at by the process of justifying and rebut-

ting claims, refining through the process an understanding 

of the topic of the argument. David Zarefsky, in Argumenta-

tion: The Study of Effective Reasoning, 2nd edition, an audio 

course produced by The Teaching Company, explains the five 

key assumptions that underlie the process of argumentation. 

First, argumentation takes place with an audience in mind 

and that audience judges ultimately the success or failure of 

the argument. Second, argumentation takes place under the 

condition of uncertainty. Third, argumentation involves justi-

fication of claims made by the arguers. Fourth, argumentation 

is a cooperative exercise; although it may seem adversarial, 

the arguers share a common goal of arriving at the best deci-

sion under the prevailing circumstances. Fifth, argumentation 

involves risks—an arguer may be shown to be wrong and lose 

the argument and the loser may lose face if s/he is perceived 

to have performed badly during the argument.

“Proof”, or justification, rests on being able to put forth 

and/or to recognize a “valid” argument. That is to say the 

argument follows logically and is thus consistent and without 

contradiction. A problem arises when we humans cannot, or 

do not make the attempt to, discern the difference between 

proof and persuasion. Persuasion, in this sense, means that 

the words sound nice, but the argument is not valid in some 

way. Recall from the earlier essay in this series Reasoning 

the words of Rick Garlikov, in which he compares reasoning 

with a game of chess. Garlikov writes, “If little children are 

playing with chess pieces and a chess board, but are making 

arbitrary moves in what they think is emulation of adults they 

have seen playing chess, it is not that they are playing chess 

badly. It is that they are not playing chess at all, regardless 

of what they think they are doing or what they call it.” If the 

rules are not followed, there is no argument in the true sense 

of the word. There is merely the melodious sound of words. 



Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 13

If I concede a point to you when you put forth an invalid 

argument, you have persuaded me, yes; but the proof or 

justification is not there.

Interlude about learning

It is most important for us to understand how knowledge is 

gained. It is for the most part a painful process based entirely 

in trial-and-error. More involved discussions about concepts 

related to learning are to be found in earlier essays in this 

series, especially Interpretation, Causation, Reasoning, and 

Patterns. I will mention briefly a few salient points.

What one is able to learn and conclude is dependent on 

how the problem is defined—that is to say, what boundaries 

are drawn that define the system being studied. Different 

boundaries lead to different questions being asked, different 

types of data collected, and different interpretations of data.

All learning of material previously discovered is based in 

ostensive definition, whereby someone is shown something 

by someone more knowledgeable about the object and the 

learner must try to figure out exactly what it is s/he is sup-

posed to be looking at (more complete discussion of this in 

Interpretation).

Abstract concepts are thought about and discussed in 

terms of metaphor. Metaphors are based in everyday expe-

rience and are related to features of human embodiment, 

for example “happiness” is discussed in terms of “up”, the 

“future” in terms of “forward”, “life” is a “journey”, and the 

like (also discussed in Interpretation). A metaphor chosen will 

necessarily highlight one aspect of the abstract concept, while 

simultaneously downplaying another aspect of that concept. 

This gets back to the problem of how boundaries are drawn 

around the abstract concept, or from what perspective the 

concept is examined.

Patterns are sought, which are converted mentally to rules 

that can then be applied to future situations. If an expected 

outcome ensues, we assume the rule must be correct. If we are 

surprised, if we see a contradiction unexpectedly or the like, 

we revise the rule and see if we can make a better prediction 

for the next event (trial-and-error at work). The rules we “dis-

cover” serve as boundaries for the system we are examining.

We start by imagining some event and then trying, “by 

hook or by crook”, to get to where we imagine. It is very dif-

ficult to get somewhere without some inkling of where one 

might be going. Serendipitous events occur, but only for the 

“prepared” mind.

True to pattern, when we find something, a method or an 

approach perhaps, we try it again and again until we finally 

are forced to admit that some sorts of problems require a dif-

ferent approach (the rules applied routinely result in surprises 

or contradictions). This is discussed in more depth in the essay 

on Reasoning.

Paradox and contradiction, if recognized, lead to the 

opportunity to redraw boundaries around a problem and try 

to “get it right.” An implicit assumption that we all hold is 

that, if we identify the pattern correctly and describe it with a 

precise and correct rule, we will avoid surprise and contradic-

tion. We are slaves to expectation!

Knowledge and understanding

Basically, while we think we “know” and “understand” 

things, we only feel that way. In the earlier essay in this series 

on Truth it was noted that when we think we know some-

thing, our “truth bell” rings in our brains. The “truth bell” 

is in the ventral striatum and associated with the nucleus 

accumbens and is associated with pleasure and motivation. 

In the earlier essay in this series on Emotion, we learned 

that Damasio posits that even the most objective thought 

we think we are having is run through various centers in the 

brain associated with feelings, including the somatosensory 

cortex. We evolved this way because being able to assess eas-

ily our feelings better enabled us to determine whether we 

were in danger imminently. When the “truth bell” rings for 

each of us, there is no assurance that the thought ringing the 

“truth bell” is actually true in the sense that it conforms with 

Universal Law.

“Evidence” is a similar concept, since it is that which jus-

tifies belief. “Belief” is a personal feeling for each of us that 

what we believe is true. Something that we accept as justify-

ing for us a belief also rings the “truth bell” and, thus, is not 

necessarily true in the conforms-with-Universal-Law sense.

“Evidence” as an attribute applied 
during argument

We all understand the world from a slightly different perspec-

tive. Each of us thinks we are correct about many of the things 

we understand. It is human nature to share knowledge and 

understanding. Often, however, the person with whom we 

are sharing our unique perspective requires convincing. To 

convince someone that our belief is justified, we offer them 

“evidence.” The evidence we offer them is the evidence that 

justifies our own belief. We assume that if the evidence is good 

enough for us, it should be good enough for anyone else and 

the evidence we are sharing should serve to justify belief in 

the mind of the other person.

Although at first blush we think of the word “evidence” 

as being associated with objectivity and science, the label 

“evidence” is laden intensely with feeling. If you reject my 

evidence, if you say my evidence is insufficient to justify your 

belief in what I believe, I infer that you are implying that my 

own belief is not justified and that I should not accept the 



14 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

item I have labeled as “evidence” as sufficient to justify my 

own belief.

The grip of “authority”

From our earliest experiences we rely on other people to tell 

us “the truth.” Our teachers, our parents initially, instruct us 

by first ostensive and then verbal definition. There is much 

to learn and learning from the experience of others saves us 

time and is often safer than direct experience. “Don’t touch 

that hot stove!”, “Don’t run into the street without looking 

both ways!”, we are told. If someone tells us this or that 

plant is safe to eat, we do not risk poisoning ourselves. To 

look to authority is natural to humans. Following authority 

helps us to become more easily acculturated into our very 

complex society.

As our lives become more complex and as we are bom-

barded from all sides by information coming with increasing 

frequency, our tendency naturally is to believe what we hear, 

since we humans look automatically to authority. It is only 

when we hear statements that we recognize as contradicting 

one another that we are prompted to examine situations 

more carefully and to make more reasoned decisions about 

what to accept as true. Contradiction requires us to ask, 

“Who really is an authority in this subject?” “Who should 

we believe?” “How can we find out the truth?” In the end, 

we look for and evaluate information put forth as “evidence” 

and we evaluate carefully those items before we accept them 

internally as evidence, which justifies our belief. For most of 

us this means adhering to the “scientific method”, which is 

defined by Encarta dictionary as “the system of advancing 

knowledge by formulating a question, collecting data about it 

through observation and experiment, and testing a hypotheti-

cal answer.” The problem here is that we must call up into 

Working Memory, which can only hold simultaneously about 

seven items, propositions that we can recognize as contradic-

tory. We all have so many potential thoughts and memories 

stored in our brains, we often do not call up information that 

is contradictory and we continue to believe contradictory 

propositions; that is we all live with cognitive dissonance.

Finding the “best fit” definition 
of a system

In the essay in this series on Reasoning, we noted that Law-

rence Slobodkin, in Simplicity and Complexity in Games of 

the Intellect, opined that complex problems require a look by 

both philosophers and mathematicians in order to gain a bet-

ter understanding of those problems. “Evidence” has been con-

sidered by both and we will see what each of them has to say.

What sorts of things can be accepted 
as evidence—philosophers

As with most abstract concepts, one’s conclusion depends 

ultimately on the boundaries one constructs around one’s 

system of thought concerning the concept.

Thomas Kelly, in Evidence published in the online Stan-

ford Encyclopedia of Philosophy, notes that most people 

think of evidence as “something that might be placed in a 

plastic bag”, such as a bloody knife, or an historical docu-

ment, or the result obtained by biochemical analysis of a 

blood specimen. However, philosophers through the ages 

have applied variably the term evidence to mental items pres-

ent in one’s consciousness (Bertrand Russell), stimulation of 

one’s sensory receptors (Willard Quine), or even the totality 

of propositions that one knows (Timothy Williamson). Bayes-

ians consider evidence to be those beliefs for which one is 

psychologically certain.

Should an item in my consciousness, say an idea I have 

for writing a story of science fiction (and, therefore, for 

which very little physical evidence is available) be considered 

as evidence? Perhaps it could serve as evidence that I have 

an imagination. Should the fact that I say I feel cold serve 

as evidence to support my action to turn up the thermostat? 

Or should I wait until someone sees me shivering so that 

more than one person agrees that I feel cold? Should the 

totality of propositions I “know” serve as evidence, even if 

all those propositions are not satisfiable with one another 

(some propositions contradict one another, if only I could 

bring them into my consciousness at the same time, I would 

see that they are contradictory and could act to resolve my 

cognitive dissonance)?

Kelly advises us that philosophers have offered “quite 

divergent theories of what sorts of things are eligible to serve 

as evidence.” He points out that, depending on one’s frame of 

reference, “the concept of evidence has often been called upon 

to fill a number of distinct roles”, and that, while sometimes 

the roles complement each other, sometimes tension is created.

One interesting concept is that, in the minds of those who 

are skeptical about our knowledge of the external world, 

one’s evidence does not favor ordinary commonsense inter-

pretations of one’s environment over unusual alternatives. For 

example, skeptics may point out that we do not sense what 

we think we are sensing; those skeptics posit that we could 

be hallucinating in an undetectable way. Our evidence does 

not mean we see that tree, even if we pluck a leaf and feel the 

features of that leaf under our fingers. We could be hallucinat-

ing the entire episode. This has been dubbed the “brains in 

a vat” paradox. Skeptics maintain that there is no way to be 

certain about anything we think we “know.”

Another interesting concept is that an item of evidence, 

E, can never be the ultimate evidence in support of a belief 



Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 15

because there is always the possibility that additional evi-

dence, E’, may become known that defeats the prior evidence. 

Evidence that is susceptible to being undermined is called 

“defeasible” evidence. Kelly points out that there is contro-

versy among philosophers whether “indefeasible” evidence 

could even exist.

Important to this discussion about the availability of 

additional evidence is whether one is considering a subset of 

evidence or a theoretical “total body of evidence.” I remem-

ber attending courses in dermatopathology given by A. 

Bernard Ackerman, M.D. Often, when Bernie was discussing 

his diagnosis of a particular case, a member of the audience 

would ask (this is a paraphrased quotation), “what if you just 

had this area—what would your diagnosis be then?” Bernie 

would point out, “but you don’t just have a small area, you 

have the entire case. It makes no sense to consider a small 

part of the specimen in isolation; you must consider all the 

information available.”

It is true that our brain power has limitations, but Bernie 

insisted that we should not draw our boundaries around a 

problem more narrowly than necessary. We will return to the 

problem of narrow boundaries later.

Additionally, evidence supports a belief in relation to the 

number of hypotheses available. If there is only one hypoth-

esis, then evidence supports only that hypothesis. But if there 

are multiple plausible competing hypotheses, evidence may 

support more than one of those hypotheses and not serve to 

differentiate between competing hypotheses.

Bayesians theorize that evidence can support an hypoth-

esis only if one considers the probability that an hypothesis 

is correct. We physicians are all familiar with Bayes theorem 

as it relates to diagnosis. If the prevalence of disease A is 

30% and the prevalence of disease B is 3%, the presence 

of a symptom common to both diseases is more likely to 

be evidence of disease A than disease B. What we need is a 

symptom or sign or test result that will serve to differentiate 

between the two diseases.

Another consideration philosophically is whether addi-

tional confirmatory evidence provides a stronger argument 

than disconfirmatory evidence. Karl Popper developed the 

example using the premise “All swans are white.” He averred 

that evidence of each additional white swan provided little 

additional proof of the claim. He pointed out that a single 

black swan would disprove the hypothesis. He pointed out 

that the goal of science should be to “look for black swans.” 

Scientific experiments should attempt to disprove an hypoth-

esis. If the experiment failed to disprove the hypothesis, that 

hypothesis could still serve as a working hypothesis and as 

a (temporary) basis for further progress of knowledge about 

some aspect of our universe.

Victor DiFate, in his entry Evidence on the Internet Ency-

clopedia of Philosophy, describes Carl Hempel’s work on 

“The Raven’s Paradox.” Hempel begins with the hypothesis 

“All ravens are black” and then draws a logically equivalent 

statement, “All non-black things are non-ravens.” Hempel 

then points out that one could provide evidence that all 

ravens are black by merely looking around the room and 

saying, for example, “That book is green. It is a non-black 

thing and a non-raven. Therefore it is evidence in support of 

my hypothesis.” He further points out that, using “evidence” 

to support a statement that is equivalent from a logical stand-

point to the original premise does not do much to prove the 

hypothesis in a meaningful way and that a similar argument 

could be used to “prove” the hypothesis that “all ravens are 

white.” A way around this, points out DiFate, might be to 

“test severely” a hypothesis. It may be true that a green book 

provides evidence that all ravens are black, but the evidence 

is weak in the extreme. One should make a good faith effort 

to ensure that, if a non-black raven exists, one is likely to find 

it, just as Karl Popper has recommended.

Philosophers have spent much time and brain power on 

the problem of evidence. The main point I wish to make here 

is that how one frames the problem determines the sorts of 

conclusions one may draw ultimately. One cannot draw a 

system with infinite boundaries and, therefore, paradoxes 

and disagreements will arise that might suggest a better, or 

at least an alternate, way to draw boundaries in an effort to 

minimize the presence and effects of paradox.

Problem definition from a 
mathematical perspective

Lawrence Slobodkin, in Simplicity & Complexity in Games 

of the Intellect, explains the role mathematicians play in 

our world. Says Slobodkin, “The work of mathematicians 

is to imagine new worlds and what their regularities might 

be. In their choice of difficult intellectual problems they can 

exclude questions that require physical apparatus for col-

lecting information and knowledge or social history in their 

answers. In this sense they are free of the limitations placed 

on empirical scientists . . . The purpose of their activity is 

clarity and understanding only. While they are free to make 

new worlds, they carefully avoid dealing with the inconve-

nient parts of this one.”

Mathematicians draw up a set of rules, which are often 

represented symbolically by formulae, they then select a set 

of initial conditions (by defining some of the variables in 

the equations), and then set the whole process in motion by 

attempting to solve the equations to see what occurs. This 

is very like the concept of games discussed in the essay in 

this series on Reasoning. Slobodkin states of games, “Basi-

cally, all good games involve a complete, circumscribed, and 

simplified model of a world, consisting of a clear playing 



16 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

field with understandable and unchanging rules whose rich 

consequences are then developed by the players.”

When mathematicians approach a problem, they set cer-

tain assumptions (which are some of the rules) and make cer-

tain predictions about what they expect will happen. If their 

predictions come to fruition, they accept that their assump-

tions are valid. If something unexpected occurs, they must 

consider whether their assumptions were correct or whether 

there could be some other reason for the unexpected occur-

rence. If a contradiction arises when the rules are executed 

flawlessly, there is a paradox.

Paradox as a clue to deficient 
knowledge

Thomas Bolander, in Self-Reference in the online Stanford 

Encyclopedia of Philosophy, writes of paradox “A paradox is 

a seemingly sound piece of reasoning based on apparently true 

assumptions that leads to a contradiction . . . The significance 

of a paradox is its indication of a flaw or deficiency in our 

understanding of the central concepts involved in it.” Bolander 

describes semantic and set-theoretic paradoxes and explains, 

“In [the] case of the semantic paradoxes, it seems that it is 

our understanding of fundamental semantic concepts such as 

truth (in the liar paradox and Grelling’s paradox) and defin-

ability (in Berry’s paradox) that are deficient. In the case of 

set-theoretic paradoxes, it is our understanding of the concept 

of the set. If we fully understood those concepts, we should be 

able to deal with them without being led to contradictions.”

For the purposes of this essay I am using the definitions, 

from Encarta, of “truth” as “correspondence to fact or real-

ity” and “definability” as ability to “give the precise meaning 

of a word or expression or to state or describe something 

clearly.” As for “reality”, I invoke the words of Steven Pinker 

(as discussed in the essay in this series on Patterns), in The 

Stuff of Thought: Language as a Window Into Human 

Nature, “But reality can’t be riddled with paradoxes and 

inconsistencies; reality just is.”

You can see that, if we humans are deficient in our under-

standing of the concepts of “truth” and “definability.” it is 

only natural that we will have difficulty understanding the 

concept of “evidence.”

Parenthetically, the paradoxes mentioned by Bolander 

are as follows. But first, a few more definitions. Logic, as 

defined in Encyclopedia Britannica, 15th edition, is the study 

of propositions and of their use in argumentation. Deborah 

Bennett, in Logic Made Easy: How to Know When Language 

Deceives You, states, “A proposition is any statement that has 

the property of truth or falsity.” A proposition is composed 

of a subject and a predicate. As per The Random House Dic-

tionary of the English Language, second edition, the subject 

is the syntactic unit that is performing the action or being in 

the state expressed by the predicate and the predicate is the 

syntactic unit that expresses the action or state attributed to 

the subject. From the standpoint of logic, the predicate is that 

which is affirmed or denied by the subject .

The liar sentence is the proposition (and thus having 

the property of truth or falsity) “This sentence is not true.” 

“Sentence” is the subject and “true” is the predicate, which 

is denied by the subject in this example. When one tries to 

determine the truth of this proposition, one either starts out 

assuming the sentence is true or that the sentence is false. 

If one assumes it is true, then it cannot be true because the 

sentence itself (self-reference) states that it is not true. If one 

assumes the sentence is false, then it must be true since the 

“false” of “not true” is “true.”

Grelling’s paradox involves the use of a predicate defined 

in a self-referent way. States Bolander, “Say a predicate is 

heterological if it is not true of itself, that is if it does not 

itself have the property it expresses. [“hetero-” being a prefix 

meaning “different or other” and “logical” meaning “based 

on facts”] Thus the predicate “German” is heterological, since 

it is not itself a German word, but the predicate “deutsch” 

is not heterological. The question that leads to the paradox 

now: ‘is “heterological” heterological?’” Bolander continues 

his explanation, “It is easy to see that we obtain a contradic-

tion independently of whether we answer ‘yes’ or ‘no’ to this 

question (the argument runs more or less like in the liar’s 

paradox). Grelling’s paradox is self-referential, since the defi-

nition of the predicate heterological refers to all predicates, 

including heterological itself. Definitions such as these, which 

depend on a set of entities, at least one of which is the entity 

being defined, are called impredicative.

Berry’s paradox is also based on an impredicative descrip-

tion. Bolander explains, “Some phrases of the English lan-

guage are descriptions of natural numbers, for example, “the 

sum of five and seven” is a description of the number 12. 

Berry’s paradox arises when trying to determine the denota-

tion of the following description: ‘the least number that can-

not be referred to by a description containing less than 100 

symbols’. The contradiction is that this description containing 

93 symbols denotes a number which, by definition, cannot be 

denoted by any description containing less than 100 symbols. 

The description is of course impredicative, since it implicitly 

refers to all descriptions, including itself.”

Russell’s paradox is a set-theoretic paradox. States Bolan-

der, “Russell’s paradox arises from considering the Russell 

set R of all sets that are not members of themselves . . . The 

contradiction is derived by asking whether R is a member 

of itself . . . If R is an element of itself, then by the definition 

of the Russell set, it is not a member of itself. If R is not an 

element of itself, then by definition, R is an element of itself.



Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 17

Language can interfere with 
logic and evidence

This section and the next few sections will address problems 

with language as we use language to attempt to provide 

logical reasons to support our claims and to use the term 

“evidence” in its ideal sense.

The vast majority of us are well-intentioned. When we 

speak to each other and argue a point, we try very hard to 

follow the rules as described by Garlikov and Zarefsky and 

others. It is just that certain limitations in the system get in 

the way of our goals as we imagine those goals. Some of these 

limitations were addressed briefly in the section in this essay 

on Interlude About Learning. Another limitation is the way 

we are able to use language.

Language serves as an instrument of thought and thought 

serves as a means to understanding. Thus language, which is 

composed of words and syntax, is the currency of understand-

ing. Encarta defines understanding as the ability to explain to 

oneself a concept and seems to imply some degree of precision 

since, in theory, we would explain to ourselves a concept in the 

same way each time we explain it, otherwise, we would not 

truly “understand” the concept if we kept changing our minds.

When we explain to ourselves, we may well understand 

the “message” in exactly the same way each time we ponder 

it, but what happens when we try to explain the concept or 

message to another person? We assume that another person 

understands language the same way we do, but study after 

study has shown that people do not understand seemingly 

simple bits of language in the same way. We all know from 

practical experience that we are often surprised by what 

ensues when we have relayed a message to someone.

Thought and logic

In earlier essays in this series, especially in Reasoning, we 

learned that the rules of logic are not the rules of our “natu-

ral” thinking processes. We looked at the work of Gerd Giger-

enzer, who in Adaptive Thinking and Gut Feelings, explains 

the concept of “fast and frugal” heuristics and the role of 

Environment of Evolutionary Adaptation in the evolution of 

what are truly our “natural” thinking processes.

Our “natural” thinking processes often lead to errors, 

although usually not life-threatening errors, which is why 

we have survived to pursue our studies. Perhaps because we 

find our errors discombobulating, if not downright embar-

rassing, we maintain steadfastly that we can “do better.” To 

that end, certain patterns of thought and language have been 

observed throughout the ages and studies have been made to 

understand rules that lead to consistent and noncontradic-

tory thought. We will examine both the rules and common 

misunderstandings of the rules later in this essay.

Rules of logic as rules 
of communication

Rules exist so that we can know what to expect. Humans, 

despite occasional protestations to the contrary, hate sur-

prises. One very important set of rules that we have relate to 

communication. Without communication we could not exist. 

And without rules, there can be no effective communication.

Bennett, in Logic Made Easy, states, “There are certain 

principles of ordinary conversation that we expect ourselves 

and others to follow. These principles underlie all reasoning 

that occurs in the normal course of the day and we expect 

that if a person is honest and reasonable, these principles 

will be followed. The guiding principle of rational behavior 

is consistency. If you are consistently consistent, I trust that 

you are not trying to pull the wool over my eyes or slip one 

by me . . . [these principles of conversation are] consistency 

and noncontradiction [which were] recognized very early on 

to be at the core of mathematical proof.”

So in a way we expect the same rigor of ordinary conver-

sation that we expect from mathematical proof. In fact, as we 

shall see, although logic is a function of language (discussed 

in the essay in this series on Reasoning) the rules of logic, 

and even messages themselves, can be written symbolically 

and the formulae and equations can even be manipulated 

by computer algorithms. Parenthetically, this should not 

surprise us much since mathematics in its purest form is the 

language of relationships (patterns) and not merely a way to 

manipulate numbers.

Common symbols used are S for subject and P for predi-

cate. For conditional propositions (if/then statements), p 

is the antecedent and q is the consequent. Aristotle noted 

that form determines the validity of an argument, regard-

less of the truth or falsity of the propositions. This allows 

the simplicity of using symbols, which in some systems are 

manipulated according to mathematical rules, to determine 

validity since one will not be distracted by the subject mat-

ter. In fact, mathematical proofs are evaluated for validity 

by computer programs developed for that purpose since to 

determine validity “by hand” is tedious, time-consuming, and 

prone to human error. Truth or falsity of propositions must 

be determined separately since only a true and valid argument 

is a sound argument (as discussed in the essay in this series 

on Reasoning).

Logic as a means of 
evaluating evidence

Many things in life are not straightforward. It may be obvious 

that “B” follows from “A”, but it may be less obvious that “G” 

or “M” or “Z” is a consequence ultimately of “A.” In order 

to get from “A” to a conclusion, “G,” we require some sort of 



18 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

“proof.” Encarta defines “proof” as “evidence or an argument 

that serves to establish a fact or truth of something.”

Keith Devlin, in Mathematics: The Science of Patterns, 

states, “In propositional logic, a proof, or valid deduction, 

consists of a series of propositions such that each proposition 

in the series is either deduced from previous ones by means of 

modus ponens, or else is one of the assumptions that underlie 

the proof.” Modus ponens, as discussed in the essay in this 

series on Reasoning, follows the form, “if p, then q.” Bennett 

explains, “The basic steps in any deductive proof, either math-

ematical or metaphysical, are the same. We begin with true 

(or agreed upon) statements, called premises, and concede 

at each step that the next statement or construction follows 

legitimately from the previous statements. When we arrive at 

the final statement, called our conclusion, we know it must 

be necessarily true due to our logical chain of reasoning.”

I want to point out early in this discussion that ultimately, 

despite all these rules we are going to examine, our decision as 

to valid or not valid, true or not true, is based in trial-and-error 

and common sense, which result from our experiences. We use 

rules, or at least attempt to use them, because we think rules 

will lead us necessarily to a correct conclusion, but if at the end 

of our intellectual labors we can think of a counterexample 

that shows our conclusion to be false in some instance, we 

know our thread of reasoning contains an error or that we have 

run into a paradox that exposes our lack of understanding.

Bennett discusses the work of Douglas Hofstadter, who, 

in the words of Bennett, “said that the study of logic began as 

an attempt to mechanize the thought processes of reasoning. 

Hofstadter pointed out that even the ancient Greeks knew 

‘that reasoning is a patterned process, and is at least partially 

governed by statable laws.’ Indeed, the Greeks believed that 

deductive thought had patterns and quite possibly laws that 

could be articulated . . . [troubled by the Sophists, who used 

‘deliberate confusion and verbal tricks in the course of a 

debate to win an argument’] Aristotle . . . attempted to sys-

tematically lay out rules that all might agree dealt exclusively 

with correct usage of certain statements called propositions.” 

Bennett describes Aristotle’s basic work in logic. Aristotle 

strived to develop methods “to reason from generally accepted 

opinions about any problem set before us and shall ourselves, 

when sustaining an argument, avoid saying anything contra-

dictory.” Aristotle’s two basic axioms were “the law of the 

excluded middle” and the “law of noncontradiction.”

Law of the excluded middle

Explains Bennett, “The law of the excluded middle requires 

that a thing must either possess a given attribute or must not 

possess it. A thing must be one way or another; there is no 

middle. In other words, the middle ground is excluded. A 

shape is either a circle or not a circle . . . A statement is either 

true or not true.” Bennett points out that this law cannot 

be applied reasonably to all situations, since “fuzzy logic” 

applies to circumstances when application of the law of the 

excluded middle is inappropriate. A common tactic in debate 

is to pretend that the law of the excluded middle applies, 

when it does not apply. An opponent is encouraged, thereby, 

to accept a position he does not hold. Examples offered by 

Bennett, “Either you are with me or you are against me. 

Either you favor assisted suicide or you favor people suffering 

a lingering death.” Recall the discussion on fuzzy logic put 

forth by Bart Kosko and described in the essay in this series 

on Reasoning. How many apples are entirely red or entirely 

green? How many people like their jobs 100% of the time? 

Inappropriate use of the law of the excluded middle is called 

the “black-and-white fallacy.”

Law of noncontradiction
Bennett describes the law of noncontradiction, “ . . . a thing 

cannot both be and not be at the same time. A figure cannot 

be both a square and not a square. Two lines in a plane cannot 

both intersect and not intersect.”

Using syllogisms

Logicians understand that the basis of argumentation is the 

syllogism. Bennett states that Aristotle defined the syllogism 

as “ . . . discourse in which, certain things being stated, 

something other than what is stated [a conclusion] follows of 

necessity from their being so.” Adds Bennett, “In other words, 

a syllogism accepts only those conclusions that are inescap-

able from the stated premises.”

Syllogisms, as series of premises related to each other 

in some way, are composed of words, and certain of those 

words appear consistently in syllogisms, defining as they 

do the relationship of the subject (S) to predicate (P) of the 

premises offered. These simple words are used often by us 

and we each assume that “the other guy” understands them 

in exactly the same manner that we understand them. But we 

do not understand words such as “all”, “a”, “any”, “some”, 

“not”, “if”, and “then” in the same way.

States Bennett, “In reasoning and language comprehen-

sion, there are several factors to consider. Sentences take on 

meaning based on the denotative (dictionary) meaning, the lin-

guistic structure (syntax and semantics), and the connotation. 

Connotation includes the factual and experiential knowledge 

that we bring to the material at hand . . . If p, then q can be 

expressed as: p never without q; p only if q; q if p; p is a suf-

ficient condition for q; p implies q; q is a necessary condition 

for p; q is implied by p; or q whenever p. Though they are 

identical statements in logic, there is no reason to believe that 

individuals interpret these sentence forms in the same way.”



Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 19

Quantifiers may be universal or particular. For example, 

“all,” “every,” and “none” are universal and specific, apply-

ing to the entire class under discussion, but the quantifiers 

“some,” “few,” and “many” are particular and vague, apply-

ing to only some members of the class under discussion.

In classifying valid conclusions, the symbols A and I are 

assigned to propositions that are affirmations (derived from 

the word AffIrmo), A for universal and I for particular, while E 

and O are assigned to propositions that are negations (derived 

from the word nEgO), E for universal and O for particular.

Aristotle discovered that for three line syllogisms there 

were sixty-four possible ways that the four types of quanti-

fiers (A, I, E, and O) could be combined, but only four of 

those combinations resulted in valid conclusions. (It seems 

that Aristotle had discovered the problems that are associ-

ated with the “combinatorial explosion” as described by 

Gigerenzer and discussed more completely in the earlier essay 

in this series on Reasoning.) Each combination is referred 

to as a “mood.” The valid moods are AAA, EAE, AII, and 

EIO. Examples of valid syllogisms are AAA—All birds are 

animals; All canaries are birds; Therefore, all canaries are 

animals; EAE—No beans are animals; All chickpeas are 

beans; Therefore, no chickpeas are animals; AII—All biogra-

phers are authors; Some curators are biographers; Therefore, 

some curators are authors; EIO—No bases are acids; Some 

chemicals are bases; Therefore, some chemicals are not acids.

Syllogisms were also classified as to “figure.” which 

referred to the arrangement of terms in the syllogism. The 

conclusion is symbolized as, for example, “All S (subject) are 

P (predicate).” Between the two premises of the syllogism, 

one contains the subject and the other the predicate of the 

conclusion. Both premises contain a common term, called 

M, the middle term. Bennett gives the example using the 

syllogism, “All poodles are dogs (first premise); All dogs are 

animals (second premise); Therefore, all poodles are animals 

(conclusion).” In the conclusion, “poodles” is S and “animals” 

is P. The first premise is S-M and the second premise is M-P, 

where “dogs” is the middle term, M. Considering the possible 

arrangements, S-M or M-S, M-P or P-M, Aristotle called the 

“first figure” S-M, and M-P, the “second figure” S-M and 

P-M, and the “third figure” M-S and M-P for the premises. 

Only the “first figure” is valid, recognized Aristotle (“All 

dogs are poodles.” or M-S, for instance, is not true). Aristotle 

resolved these syllogistic moods by applying his Law of Non-

contradiction and settled ultimately on the rules we now use.

Reductio ad absurdum as proof

Bennett describes the basic steps in any deductive proof. 

One begins with true or agreed upon premises and concedes 

at each step that the ensuing statement follows legitimately 

from the previous statement(s). The final statement is the 

conclusion. A common type of proof is one of reductio ad 

absurdum, by which one arguer begins by accepting the 

opponent’s premise as true and argues logically by refutation 

to a contradiction by exposing inconsistencies in the oppo-

nent’s original argument, causing the opponent to give up his 

original premise as false. In all systems, agreement on the rules 

and definitions used in the system of interest is essential to 

maintaining consistency, so that reasoning in that system can 

be valid. For example, there is a difference between contra-

dictories and contraries. Confusing one for the other can lead 

to invalid arguments and unsound conclusions.

Contradictories versus Contraries

Contradictories are paired statements such that both state-

ments cannot be true and both cannot be false. For contra-

dictories, one statement is universal (affirmation or denial) 

and its contradictory is particular (denial or affirmation, 

respectively). For example, “every person has enough to eat” 

is a universal statement, applying as it does to an entire set. 

The contradictory must be a particular (and not a universal) 

denial—“some people do not have enough to eat.” A particu-

lar applies to a subset, not to the entire set (humans in this 

example). In another example, “No individuals are altruistic” 

serves as the universal denial, while “some people are altruis-

tic” serves as the particular affirmation in this contradictory 

pair. Aristotle pointed out that every affirmative statement has 

its own opposite negative and vice versa. For contradictories, 

one statement of the pair will always be true and the other 

false. Contradictories are represented by A with O and E with 

I in AffIrmo/nEgO terminology.

Contraries consist of opposite pairs in which both the 

affirmation and denial are universal or both are particulars. 

For contraries, both cannot be true, but it is also possible that 

neither is true. For example, “All people are rich” and “No 

people are rich” are contraries. Contraries are represented 

by A with E and I with O in the AffIrmo/nEgO terminology.

Bennett credits John Stuart Mill with noting that people 

frequently confuse contradictories with contraries and that 

this confusion also occurs in one’s private thoughts. He 

opined that if people made these pairs of statements aloud 

they may detect their errors.

Bennett gives as example the common plaint “Nobody 

around here helps out.” The contradictory is that “Some of 

us help out.” and the contrary is “We all help out.” How often 

is the appropriate affirmation used in the heat of complaint?

Using quantifiers in logic

Quantifiers, mentioned in an earlier section in this essay, may 

be expressed explicitly or implicitly, and this variation in 

usage can lead to alternate interpretations. Consider the uni-



20 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

versal quantifier “all.” Bennett gives the example, “Members 

in good standing may vote.” “All” is implied. The article “a” 

may be used as a universal quantifier, as in the example, “A 

library is a place to borrow books.” implying “all” libraries. 

Confusion may arise in deduction logically by using different 

universal quantifiers. Bennett cites a study in 1989 by David 

O’Brien in which people of various ages (second graders, 

fourth graders, eighth graders and adults) were tested for 

their understanding of the universality of “all,”, “any,”, and 

“a” used in propositional statements. States Bennett, “With-

out exception, in every age group the tendency to err was 

greatest when the indefinite article a was used, “If a thing . . 

.” For older children and adults, errors decreased when any 

was used, “If any thing . . . ,” and errors virtually vanished 

with the universality was made explicit, “all things . . .” With 

the youngest children, though the errors did not vanish, they 

were reduced significantly when the universality was made 

clear with the word all.”

Problems with converse statements

Beginning with the basic form of a propositional statement, 

“quantifier subject (S) predicate (P)”, the statements “All S 

are P” and “All P are S” are converse statements. People may 

think they mean the same thing, but that is not a correct 

interpretation. Bennett states that conversion is a common 

error during argument. Both statements may be true, but 

they are not equivalent statements. Bennett gives examples 

“All mothers are parents” versus “All parents are mothers.” 

The first statement is true, but the second is not true. “All 

dogs love their owners” versus “All (dog) owners love their 

dogs.” Possibly neither statement is true. Bennett describes a 

study in which children of varying ages were asked about a 

series of drawings of squares and circles. The children were 

shown a picture in which, from left to right, were drawn a 

gray circle, a white square, a gray circle, a white square, a 

gray square, a gray circle, a gray circle, and a gray square. 

The children were then asked questions such as “Are all the 

squares white?” (considered by the examiners an easy ques-

tion), “Are all the circles gray?”, and “Are all the white ones 

squares?” (considered by the examiners a more difficult ques-

tion). States Bennett, “The youngest subjects converted the 

quantification 50% of the time, thinking ‘All the squares are 

white’ meant the same as ‘All the white ones are squares’. This 

may be explained in part by the less developed language abil-

ity of the youngest children (ages 5-6), but their mistakes may 

also be explained by their inability to focus their attention on 

the relevant information [such as just squares or just white 

things] . . . By ages 8 and 9, children were able to correctly 

answer the easier questions 100% of the time and produced 

the incorrect conversion on the more difficult questions only 

10 to 20% of the time.”

Another factor involved in reasoning is that of familiarity, 

or lack thereof, with the subject being reasoned about. States 

Bennett, “The rules of inference dictating how one statement 

can follow from another and lead to logical conclusions are 

the same regardless of the content of the argument. Logical 

reasoning is supposed to take place without regard to either 

the sense or truth of the statement or the material being 

reasoned about. Yet, often reasoning is more difficult if the 

material under consideration is obscure or alien.”

Recall from the essay in this series on Reasoning Gigeren-

zer’s comparison of performance of test subjects on the Wason 

Selection Task. One group was asked to reason about the 

cards “D,” “E,” “3,” and “4.” while the other group was asked 

to reason about the cards “subway”, “Arlington”, “cab”, and 

“Boston.” Gigerenzer’s hypothesis was that, if logic is “natu-

ral” thought, most test subjects should perform correctly 

whether the problem was abstract (as in the D, E, 3, 4 sce-

nario) or whether the problem concerned social interactions 

(as in the subway, Arlington, cab, Boston scenario). The tests 

were quite similar from a logical viewpoint. When the four 

cards on the table read “D,” “E,” “3,” and “4.” the conditional 

statement to be evaluated logically was “If there is a ‘D’ on 

one side of the card, then there is a ’3’ on the other side.” The 

test subjects were instructed to turn over any cards necessary 

to test the validity of the conditional statement. Logic would 

dictate that, faced with a statement “If P, then Q,” one must 

rule out, “P and not Q.” The appropriate cards to turn over 

are “D” and “4.” In other scenario, when the four cards on the 

table were “subway,” “Arlington,” “cab,” and “Boston”, the 

conditional statement to be evaluated was “If a person goes 

to Boston, then he takes the subway.” The cards to turn over 

are P (Boston) and not Q (cab). Gigerenzer found that 10% 

of test subjects answered correctly in the abstract scenario 

and 30-40% of test subjects answered correctly in the social 

scenario, a much better performance; however, one might 

be tempted to conclude from this study that, even under the 

best of circumstances, less than half of us can think logically.

Bennett points out that familiarity is not always a help. 

She describes a study performed in 1928 by M. C. Wilkins. 

The premise put forth to Wilkins’ students was “All fresh-

man take History I.” States Bennett, “ . . . only 8% of her 

subjects accepted the conversion, ‘All students taking History 

I are freshmen.’ However, 20% of them accepted the equally 

erroneous conclusion, ‘Some students taking History I are 

not freshmen.’ With strictly symbolic material (All S are P), 

the errors ‘All P are S’ and ‘Some P are not S’ were made by 

25% and 14% of the subjects, respectively. One might guess 

that in the first instance students retrieved common knowl-

edge about their world—given the fact that all freshmen take 

History I does not mean that only freshmen take it. In fact, 



Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 21

they may have themselves observed nonfreshmen taking His-

tory I. So their conclusion was correct and they were able to 

construct a counterexample to prevent making the erroneous 

conversion. However, as they continued thinking along those 

lines, knowledge about their own world encouraged them 

to draw a (possibly true) conclusion that was not based on 

correct logical inference. ‘Some students taking History I are 

not freshmen’ may or may not be true, but it does not follow 

logically from ‘All freshmen take History I’.”

Negation

The interplay between language and logic can prove espe-

cially troublesome. As Bennett pointed out earlier, statements 

that are equivalent in meaning by logic are not always inter-

preted as equivalent by a human reasoner. Negation, or saying 

that something is not, proves difficult at times for humans 

to process. Bennett explains that Aristotle recognized early 

on in his studies that propositions meaning the same thing 

can be explained as either an affirmation or a negation. For 

example, “all humans are imperfect” is the affirmation, while 

“no humans are perfect” is a negation with an equivalent 

meaning. It is possible to affirm the absence of something or 

to deny the presence of something; thus, the same set of facts 

can be presented by affirmation or negation.

How facts are presented, however, affects how people 

understand them. Bennett describes a study in which test sub-

jects were asked to perform certain written tasks. Test subjects 

were timed and their accuracy assessed. Basically, the same 

instruction was written as an affirmative, an implicit negative, 

and an explicit negative. Papers were given to the test subjects, 

each with the Arabic numerals 1 through 8 listed consecutively 

at the top of the page. One instruction said, “Mark the num-

bers 1, 3, 4, 6, 7.” The next instruction said, “Do not mark 

the numbers, 2, 5, 8, mark all the rest.” The third instruction 

said, “Mark all the numbers except 2, 5, 8.” States Bennett, 

“The subjects performed the task faster and with fewer errors 

of omission following the affirmative instruction even though 

the list of numbers was considerably longer.

Subjects performing the task using ‘except’ were clearly 

faster than those following the ‘not’ instruction, signifying 

that the implicit negatives were easier to understand than the 

instructions containing the word ‘not’.” Bennett adds about 

the understanding of implicit negatives, “Some negatives do 

not have an implicit negative counterpart, and those negatives 

are more difficult to evaluate. The statement, ‘The dress is not 

red’ is harder to process than a statement like ‘Seven is not 

even’, because the negation ‘not even’ can be easily exchanged 

for ‘odd’, but ‘not red’ is not easily translated [and very dif-

ficult to visualize]. The difficulties involved with trying to 

visualize something that is not may well interfere with one’s 

ability to reason with negatives. If I say that I did not come 

by car, what do you see in your mind’s eye? It may be that, 

wherever possible, we translate negatives into affirmatives to 

more easily process information.”

Double negatives can cause problems with processing 

information as well. In reasoning by reductio ad absurdum, 

we want to prove a proposition, P, but to do so we assume 

not-P and argue to a contradiction. We conclude “not-not-P” 

or “P.” Bennett points out that referendum questions at the 

voting booth often use wording that makes one’s choice seem 

counterintuitive and confuses voters. Her example is from 

a ballot managing her retirement funds. “Proposal: To stop 

investing in companies supporting gun control . . . voting ‘for’ 

means you are against gun control [are for easily obtainable 

guns] and voting ‘against’ means you favor gun control [are 

against easily obtainable guns] . . . If the process of negation 

involves an extra mental step, a double negative can be mind 

boggling. ‘The probability of a false negative for the preg-

nancy test is 1%’ or ‘No non-New Yorkers are required to 

complete form 203’ or ‘The statistical test indicates that you 

cannot reject the hypothesis with no difference’ can cause 

listeners to scratch their heads (or give them a headache).”

In a line from a story from John Mortimer’s Rumpole of 

the Bailey, Horace Rumpole, barrister at law, cross-examines 

an expert witness on the subject of bloodstains. The witness 

states, “The finding is not inconsistent with your hypothesis.” 

An exasperated Rumpole counters, “Does not ‘not inconsis-

tent’, when translated to plain English, mean ‘consistent’?” 

The witness: “Yes, it does.” Common sense reigns, albeit 

temporarily, at last.

A brief recap

So far we have seen that, although rules have been discovered 

that assist us in reasoning logically so that we might evaluate 

“evidence” according to an ideal, problems with the use of 

language, resulting as it does in differences in interpretation, 

often interfere with the ideal of formal logic to which we 

aspire. Also, speaking from the standpoint of philosophy, we 

may not even understand fully the concepts of “truth” and 

“definability” since paradoxes exist involving those terms. 

There is disagreement about what sorts of things should be 

allowed to be considered evidence. Nonetheless, each of us 

on some level think we understand what “evidence” is and 

that “evidence” is, or at least should be, true and unassailable. 

This leads to a cognitive dissonance that simmers just under 

our awareness and causes problems for us as we interact with 

our fellow man.

Evidence Based Medicine

The cognitive dissonance we all experience relative to evi-

dence spills necessarily over into our professional lives. Today, 



22 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

we are all expected to practice so-called Evidence Based 

Medicine. To do otherwise, we are told, is to risk unnecessar-

ily patients’ lives and to cause too much money to be spent 

on healthcare.

So what is meant by evidence in the case of Evidence 

Based Medicine? Despite a well-meaning start, pretty much 

“evidence” in medicine has come to mean the outcome of 

a clinical trial, that outcome having been interpreted by an 

expert in the field.

At its outset, the premise underlying Evidence Based 

Medicine was that each physician, having completed his or 

her studies of basic medical science (anatomy, physiology, 

pathology, pharmacology and the like), would determine 

for each patient the best course of action by doing his/her 

own research of the literature. By doing so, each physician 

would break the bond to “authority.” No longer would each 

physician “parrot” what s/he thought a mentor would do in a 

similar situation. S/he would find out the results of the latest 

studies and act according to the “best evidence.”

What ensued, however, was a distortion of the ideal. 

Maya Goldenberg, in “Iconoclast or creed? Objectivism, 

pragmatism, and the hierarchy of evidence” in Perspectives 

in Biology and Medicine, states, “Objectivity is an epistemic 

virtue in science that stands for an aperspectival ‘view from 

nowhere’, certainty, and freedom from bias, values, interpre-

tation, and prejudice. Even if objectivity cannot be achieved, 

it is perceived to be an ideal worth striving for.”

Goldenberg explains that the idea for Evidence Based 

Medicine arose from the “pragmatism” movement in philoso-

phy, a movement founded by Charles Sanders Peirce and Wil-

liam James. The doctrines underlying pragmatism are “(1) the 

meaning of concepts is to be sought in their practical bearings; 

(2) the function of thought is to guide action; and (3) truth 

is preeminently to be tested by the practical consequences of 

belief.” Goldenberg quotes James stating that pragmatism 

stands for “the open air and possibilities of nature, as against 

dogma, artificiality and the pretense of finality in truth . . . 

[pragmatists] turn toward concreteness and adequacy, towards 

facts, towards action, and towards power. That means the 

empiricist temper regnant, and the rationalist temper sincerely 

given up . . . [pragmatism] does not stand for any special 

results [or doctrines]. It is a method only.”

Goldenberg agrees that the allegiance of Evidence Based 

Medicine to the Randomized Controlled Trial captures the 

tenor of pragmatism; however, the strict adherence of Evidence 

Based Medicine to its hierarchy of evidence, which is based in 

a ranking of study designs based on the supposed rigor of their 

methodology, goes against the spirit of pragmatism.

Of hierarchies, Kirstin Borgerson, in “Valuing evidence: 

bias and the evidence hierarchy of evidence-based medicine” 

in Perspectives in Biology and Medicine, states that Evidence 

Based Medicine advocates “are not just claiming that it is 

helpful to be able to distinguish, for instance, good from 

bad RCTs [Randomized Controlled Trials] or better from 

worse cohort studies. They have made an assumption about 

the necessity of ranking these methods against one another 

so that a critical review of the literature will produce one, 

hopefully decisive, answer . . . [there are multiple possible 

hierarchies] . . . no one has seriously (that is, explicitly and 

methodologically) argued for any particular hierarchy. Hier-

archies are more often asserted than argued for.”

Performance of Randomized Controlled Trials (RCTs) is 

a pragmatic methodology, writes Goldenberg, since the pur-

pose of them is to “temporarily suspend prior knowledge of 

human physiology, disease, and pharmacology, all of which 

might allow for inferences regarding the effectiveness of a 

particular drug in treating a given condition, and instead 

determine whether a treatment works by trying the treat-

ment in a large number of cases under controlled conditions.” 

Goldenberg explains that RCTs are “ostensibly unhindered 

by the pre-theoretic expectations and commitments that 

can bias the deductive methods of basic science and the less 

systematic experimental methods of clinical experience and 

observational studies . . . Absent the influence of anticipated 

outcomes, scientists faced with recalcitrant empirical data 

should be more open to revising even well-established views 

about treatment efficacy.”

Goldenberg points out that randomization and blinding 

are not always appropriate. Small sample size renders ran-

domization futile, for example, and blinding is not always 

possible, as in studying the negative effects of smoking. Ethi-

cal considerations arise in studying effects of surgery, since 

sham surgical procedures would be required to truly blind 

interpretation of results. Furthermore, some social contexts 

may result in bleeding of effects of the study if, for example, 

study patients share their medications with friends participat-

ing in the study, hoping that everyone will benefit from a new 

therapeutic agent. In a blinded study, subjects may have an 

incentive to lie about their actions, if they fear being repri-

manded for breaking the blinding effect of the study.

The hierarchy of Evidence Based Medicine asserts that 

Randomized Controlled Trials are always better evidence than 

alternative studies such as observational studies, even though 

different health research studies call for different designs so 

there really is no gold standard methodology. For example, 

Robin Bluhm, in “From hierarchy to network: a richer view 

of evidence for evidence-based medicine” in Perspectives in 

Biology and Medicine, states of studies of epidemiology, “ 

. . . epidemiology is not generally an experimental science. 

The epidemiologist must try to identify causal factors ‘in the 

wild’ rather than in the controlled environment of the labora-

tory.” Bluhm points out that progress in medicine requires the 

close interaction of epidemiologists, who attempt to establish 

causes of disease, and laboratory scientists, who can design 



Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 23

experiments to compare outcomes between study and control 

groups. The most common study design for epidemiology, 

asserts Bluhm, is the cohort study, in which groups, similar 

in most ways, differ in a finding of interest, and are observed 

and compared over time to determine if the finding of interest 

leads to a different incidence of a separate finding at the later 

time. For example, is smoking associated with an increased 

incidence of lung cancer, or is a high cholesterol level associ-

ated with an increased incidence of myocardial infarction?

Cohort studies are similar to Randomized Controlled 

Trials in that the populations are followed over time. In the 

cohort study one population is exposed to some factor, while 

in the RCT one population receives an intervention, such as 

a drug or surgical procedure. Other sorts of studies include 

case reports and cross sectional surveys. Different types of 

studies have varying strengths and weaknesses.

Goldenberg discusses the work of Upshur and Tracy, “ 

. . . the entire edifice of evidence hierarchies is . . . based upon 

expert judgment or consensus. They charge that ‘the structur-

ing of evidence according to hierarchy is by no means natural, 

intuitive, or even logically justified’ . . . Upshur and Tracy 

propose that the initial creation of an evidence hierarchy 

was intended to link the quality of evidence to the soundness 

of the recommendations based on the evidence . . . on the 

belief that these methods [RCTs and meta-analyses] are less 

susceptible than observational designs to bias. The key is the 

ability of randomization to eliminate selection bias and the 

unprovable claim that randomization balances all relevant 

known and unknown factors in a probabilistic sense. The 

hierarchy attributes lower reliability to expert judgment, and 

specifically subordinates theory and pathophysiological rea-

soning to designs with randomization. The reasoning behind 

the latter subordination is unclear, as pathophysiology often 

provides more fundamental understanding of causation and is 

in no way scientifically inferior. Thus, Upshur and Tracy con-

clude, the hierarchy has been advanced on the basis of expert 

opinion rather than reasoned argument—a move unbefitting 

of evidence-based thought and practice.”

Goldenberg asserts that adherents of Evidence Based 

Medicine have failed to recognize the fallibility of scientific 

evidence, preferring instead to undertake a “sort of absolut-

ist search for certainty.” She discusses the work of Paul Fey-

erabend who “described science as being obsessed with its 

own mythology of objectivity and universality.” Goldenberg 

continues, “If the hierarchy of evidence was put in place to 

refute skepticism and ensure certainty, it stands as an example 

of what Feyerabend abhorred: science making claims to truth 

well beyond its actual capacity.”

Mark Tonelli, in “Evidence-free medicine: forgoing evi-

dence in clinical decision making” in Perspectives in Biology 

and Medicine, opens his article, “At some time in the not-too-

distant past, medicine was apparently practiced in the absence 

of evidence. I know this to be the case because a Medline 

search for the term ‘evidence-based medicine’ prior to 1990 

yields virtually no returns . . . By the time I had completed 

residency and fellowship in 1996, evidence-based medicine 

(EBM) had gone from ‘paradigm shifting’ concept to widely 

accepted dogma.”

Tonelli bemoans that establishing hierarchies of evidence 

has distracted the medical profession from its calling, which 

is to arrive at the best possible decision, be it diagnosis or 

treatment, for the individual patient. Says Tonelli, “ . . . the 

myriad attempts to define, categorize, and stratify evidence 

for use in clinical medicine have only resulted in a epistemic 

and linguistic morass . . . Instead of arguing about what does 

or does not constitute evidence in support of a clinical deci-

sion, we should more carefully examine the central question 

regarding the legitimacy of various potential facts and war-

rants for clinical decision making.”

Tonelli notes that clinical medicine does not lend itself 

to formal, deductive logic, but utilizes the informal logic of 

argumentation. States Tonelli, “Clinical judgment requires the 

use of various kinds of reasoning. Done well, clinical decision 

making closely resembles the structure of argumentation, 

with careful consideration of many facts, warrants, backings, 

and rebuttals, ultimately resulting in a conclusion that is only 

probably, never demonstrably, correct.” Tonelli refers to the 

work of Toulmin, The Uses of Argument, noting, “ . . . data, 

or basic facts, are often invoked as a foundation to a claim, 

but that facts alone are inherently insufficient to provide 

legitimate support to any claim.

In arriving at or defending a particular conclusion, we 

must go beyond producing facts to providing warrants, more 

general and hypothetical propositions that are necessary to 

have the particular fact support a particular claim.”

Tonelli opines that proponents of Evidence Based Medi-

cine consider fact and warrant as a bundle—the fact serves 

as its own warrant. He gives the example that a certain 

pitcher may be considered the best based on a low Earned 

Run Average (ERA)—the fact. But, maintains Tonelli, the 

arguer of this claim must warrant that the ERA is superior 

to all other measures of pitching excellence to back his claim. 

Physicians, asked about their evidence for a certain decision, 

often merely cite a reference. They do not then warrant their 

use of that reference-datum by explaining why it is superior 

to other possible choices in this particular patient at this 

time. Tonelli insists that it is most important to show that the 

warrants that are invoked to support a claim based upon the 

facts in the reference are legitimate. He adds that establishing 

legitimacy of a warrant requires “an understanding of the 

underlying metaphysical and epistemic underpinnings of a 

healing discipline.”

Tonelli recognizes five broad classes of legitimate poten-

tial warrants: pathophysiologic rationale, results of clinical 



24 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

research, clinical experience, patient goals and values, and 

system features. He notes that the relative importance of any 

warrant will depend on the specifics of the patient. A warrant 

from any of the five classes may be the most important in a 

particular case. Since the classes of warrants “differ from one 

another in kind, not in degree . . . no meaningful hierarchies 

of potential warrants can exist across the [classes].” Within 

a class, a basic hierarchy might be appropriate. For example, 

the clinical experience of a medical student would likely carry 

less weight than the experience of the attending generalist, 

whose experience would carry less weight than a specialist. 

However, even within a class of warrants, hierarchies “must 

be considered general and not prescriptive, serving only as 

guidelines, not clinical rules . . . often facts and warrants 

from each of the five classes are likely to be coherent, all 

supporting the same clinical decision . . . [but] when warrants 

conflict, supporting different conclusions regarding the right 

diagnosis or course of action . . . the clinician’s judgment is 

put to the test.”

Tonelli opines, “The demand for evidence distracts clini-

cians, requiring them to search outside of the clinician-patient 

relationship for answers to questions that are not directly 

applicable to the patient at hand . . . The answer to a great 

many important and interesting general medical questions 

can be discovered by searching, analyzing, and interpreting 

published clinical research. The answer to the question of 

what to do about the individual patient, however, does not 

exist outside of the clinician-patient relationship waiting to 

be discovered.”

Tonelli observes, “The consummate clinician is one who 

can identify all the relevant facts and warrants and, when 

necessary, negotiate between conflicting warrants by weigh-

ing each in the context of the particular patient at hand. The 

excellent clinician must, by necessity, have a well-developed 

knowledge base that includes understanding of biologic and 

physiologic concepts and principles, the relevant clinical 

research in her specialty, substantial personal experience, and, 

preferably, access to clinicians with even more. In addition to 

this knowledge base, the clinician must also have the skills 

and inclination to understand patient preferences, goals, and 

values, as well as an understanding of the facilitators and 

barriers to optimal care inherent in the system in which she 

practices. No wonder EBM’s simple five-step process has 

such appeal. Training clinicians to practice an evidence-free 

medicine is significantly more challenging than training them 

to practice EBM.”

Parenthetically, the “simple five-step process” of Evidence-

Based Practice is as follows: 1) Formulate a well-built ques-

tion, 2) Identify articles and other evidence-based resources 

that answer the question, 3) Critically appraise the evidence 

to assess its validity, 4) Apply the evidence, and 5) Re-evaluate 

the application of evidence and areas for improvement. Rela-

tive to step three, family practitioner Ross Upshur, in “Look-

ing for rules in a world of exceptions,” in Perspectives in 

Biology and Medicine, noted that it had been estimated that 

“a physician would need to spend 627.5 hours just to read 

the 7,287 articles relevant to primary care each month. And 

that is just reading, never mind the “critically appraise” part.

So Evidence Based Medicine seems to be another distor-

tion of the profession of medical practice, along with the 

expectation that no errors are tolerable or should occur while 

we care for our patients, that we can take care of the total 

needs of a patient in a seven minute office visit, and similar 

expectations with which we are all familiar.

Attributed to Albert Einstein is the saying “All things 

should be made as simple as possible, but not simpler.” Slobod-

kin has pointed out, in Simplicity & Complexity in Games of 

the Intellect, that it is human nature to simplify some aspects 

of life and to complexify (for example by ritual) other aspects 

of life. We all decry “error” in the practice of medicine. But 

how much of the aggregate of unexpected and less than 

desired outcomes is really due to error per se, how much is 

due to unreasonable expectation on the part of patients and 

ourselves as medical practitioners, and how much is due to a 

lack of understanding (because we humans simply have not 

yet made the discoveries) of basic science, clinical medicine, 

and principles of complexity theory or system theory?

It seems that perhaps Evidence Based Medicine has 

evolved into an attempt to simplify the practice of medicine 

too much.

Conclusion

In the end, it seems to me that “evidence” truly is, as defined, 

“that which justifies belief” and nothing more. We each feel 

justified in believing what we believe. If our belief comes to us 

by revelation or authority, we still consider it a belief and we 

feel justified in believing it. If this is true, then evidence is best 

considered just another word for a “reason” or “reasons.” 

Attempts have been made throughout the ages to give “evi-

dence” a “higher calling” by insisting on proof that something 

labeled as “evidence” is true and warrants any conclusions 

drawn from that evidence. But, as we have seen in this essay, 

there are so many factors involved, from language to educa-

tion to paying attention to the proper things at the moment of 

reasoning, that the formal rules discovered are likely to never 

be our “natural” process of thinking. Where most of us are 

concerned, the pretense of “evidence” to a scientific ideal is 

merely an illusion. As Garlikov might say, we have not learned 

the rules of the game to use evidence as ideal.

Evidence is the aggregate of reasons we use to justify our 

belief in some fact or claim. Those reasons may or may not 

follow the rules of argumentation and those reasons may not 



Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3 25

actually lead an astute reasoner to conclude our claim. In 

the end, evidence does not guarantee truth or certainty. The 

label “evidence” applied to a fact does not make that fact any 

more likely to support a valid conclusion. What is important 

is the process we use to support a claim, the process of argu-

mentation, by which we warrant why a piece of evidence is 

pertinent to the claim.

We hold in our minds the ideal that evidence is true and 

unassailable, but we can never reach that ideal and for a 

number of reasons. We are limited by our understanding of 

basic concepts, such as “truth” and “definability”, that lead 

unavoidably to paradox. We cannot possibly ensure that we 

understand the same message in exactly the same way, nor 

do we understand the most basic concepts of our language 

in the same way, for example dealing with “if/then” hypoth-

eses, negations, and the like. We all live unavoidably with 

cognitive dissonance, believing contradictory statements, 

most often because we cannot drag the contradictions into 

our working memories simultaneously to recognize that they 

are contradictory.

Nonetheless, in a manner analogous to discovering the 

rules of logical thought, a process begun in earnest by Aristo-

tle, following the principles of the scientific method, whereby 

hypotheses are tested according to a body of organizing 

principles and the test results are examined and interpreted 

independently by multiple investigators, seems to provide the 

best way to advance knowledge, while minimizing opportuni-

ties for inconsistency and contradiction. Argumentation and 

science share the same basic principles in that people with 

differing views are willing to look at a problem from different 

perspectives and are willing to risk being proved wrong in the 

interest of acquiring a common understanding of an issue.

Reasons, properly warranted, comprise the best form of 

evidence, evidence serving as a means to the end of gaining 

knowledge. However, human nature being what it is, we 

sometimes “put the cart before the horse” and think that the 

end justifies the means. If we imagine a desired end and then 

create a “story” that we label as “evidence” for the purpose of 

persuasion only, if we put consistently the goal of winning an 

argument ahead of better understanding, as Aristotle accused 

the Sophists of doing, then we are lost.

In a manner analogous to vaccination to minimize the 

spread of infectious disease, the vast majority of people should 

take the time to understand more fully the rules of logic and 

the common problems that interfere with thinking consistently 

and without contradiction. Then the populace at large would 

be at least in a position to know a reasoned argument when 

confronted with such an animal. Michael Shermer, as dis-

cussed in the essay in this series on Interpretation, has pointed 

out, “Anecdotal thinking comes naturally; science requires 

training.” It is up to each of us to do our part to further the 

common cause of ensuring that our collective knowledge base 

is as consistent and noncontradictory as possible.

Upshur, in “Making the grade: assuring trustworthi-

ness in evidence” in Perspectives in Biology and Medicine, 

quotes Alfred North Whitehead (1929), “The chief danger to 

philosophy is narrowness in the selection of evidence. This 

narrowness arises from the idiosyncracies and timidities of 

particular authors, of particular groups, of particular schools 

of thought, of particular epochs in the history of civilization. 

The evidence relied upon is arbitrarily biased by the tempera-

ments of individuals, by the provincialities of groups, and by 

the limitations of schemes of thought.”

When confronted with inconsistencies and contradiction, 

we must try to discover the source of inconsistency or contra-

diction. We may find, by reviewing and applying assiduously 

the known rules of logic, an error in our proof. We can be 

aware of our biases and try to think more broadly. We can 

ask ourselves if we are being a bit slavish to authority. If a 

true paradox arises, we can try to expand the scheme of our 

thought and try to look at the problem from a new perspec-

tive from which paradox disappears.

Parenthetically, as an example, for Zeno’s paradox involv-

ing infinity, Zeno proposed that Achilles could never catch up 

to or pass the tortoise, who started with a 10-meter head start, 

in the race because he (Achilles) would only close a certain 

percentage of the gap in what mathematically is represented 

by an infinite series. Manipulating the formula mathemati-

cally gives a finite equation, showing that Achilles draws 

level with the tortoise when the tortoise has moved 1 and 1/9 

meters. A better understanding of infinite series eliminated 

the paradox. I am not sure we are yet ready to solve the liar’s 

paradox, but theoretically, as suggested by Whitehead, we 

could look at the problem from another less limited perspec-

tive to solve the paradox. But, as Bolander explains, that 

will require a new understanding of “truth.” Until we better 

understand truth, we must stop thinking of “evidence” as 

true and unassailable. And we should understand that our 

collective knowledge base has necessarily items in it that will 

require revision in the future.

I think it is most important that we learn more about the 

limitations of humans and to ensure that as many of us as 

possible have access to that knowledge. Only then will we be 

able to design systems that are effective, including an effec-

tive healthcare system. That humans have imagination is both 

boon and bane. Imagination has enabled us to survive, to 

prepare for the future, and to dream of a better world. But the 

downside of this is that we are tempted to believe that what 

we imagine is true and/or attainable, regardless of whether or 

not we truly understand “reality,” or principles of Universal 

Law. We are in danger, as Goldenberg said of Feyerabend’s 

words, of making claims to truth well beyond our capacity. 



26 Practical, Conceptual or Educational Notes  |  Dermatol Pract Concept 2014;4(1):3

Learning to accept “evidence” for what it really represents 

instead of what we want it to represent will be a start.

Summary

We tend to think of evidence that it must be of necessity true 

and unassailable, but that does not conform to reality. Evi-

dence is really just a reason or reasons that we use to justify 

our beliefs. We try to hold evidence to an ideal, but because 

of our innate fallibility, which occurs as a direct result of 

our evolution within the environment with which we have 

co-evolved, we cannot ensure evidence meets that ideal. The 

nature of language and the use of that language by us is a 

major impediment to maintaining consistency and avoiding 

contradiction in our communication with one another. Addi-

tionally, our “natural” thought processes do not follow the 

rules of logic as discovered by logicians throughout the ages. 

This being the case, we must endeavor to understand better 

our human fallibility and learn to work within our capabili-

ties. To do so, we must accept “evidence” as what it is instead 

of what we would like it to be.

Dr. Anderson is a retired general pathologist, residing in Carbon-

dale, Illinois, and teaching part-time at her alma mater, Southern 

Illinois University School of Medicine.

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