











































[Expositions 6.2 (2012) 23-32]  Expositions (online) ISSN: 1747–5376 
 

What Can We Know of What the Romans Knew?  
 
JACQUELINE FEKE 
University of Chicago 
 

 
In What Did the Romans Know? (2012) Daryn Lehoux paints a complex portrait of Roman 
intellectual life. Ethical, political, and cultural traditions inform the conventions of scientific 
inquiry and fact-making. He at once presents a broad network of intellectual artifacts – he 
examines a plethora of texts, such as by Cicero, Lucretius, Ptolemy, and Galen – and he offers a 
deep analysis of how ancient history may inform the philosophy of science, and vice-versa. A 
common thread through the monograph consists in attempts by philosophers, ancient and 
modern, to propound realism in the face of skeptical challenges, to assert that scientific theories 
are true and that it is possible to know that they are true. Lehoux adopts a pragmatist theory of 
truth and justification, and he argues that Roman philosophers, mathematicians, and physicians 
were justified in asserting the truth of their scientific theories.  

In the following, I examine three components of Lehoux’s multi-faceted argument. First, I 
address his proof of the existence of the concept of natural law in the Roman period, well before 
the sixteenth century, its generally accepted terminus post quem. Lehoux divorces the 
terminology “law of nature” from what he takes to be the concept’s essential content, regularity 
in nature. Once the concept is free of its philological constraints, Lehoux argues that historians 
may justifiably take the account of planetary stations in Ptolemy’s Almagest, for instance, to 
function as a law of nature, even though the text does not label it a law as such. I attempt to 
bridge philology and content by analyzing Ptolemy’s accounts of law and reason in On the 
Kritêrion and Hêgemonikon and the Harmonics. I argue that an analogy comparing law and 
regularity in nature is consonant with Ptolemy’s epistemology and, therefore, despite the fact that 
Ptolemy does not use the phrase “law of nature,” the metaphor suits his philosophy of science. 
Second, I address in what way Ptolemy’s epistemology responds to the so-called “Skeptical 
challenge”, as Lehoux contends. Third, I examine Lehoux’s own response to the Skeptical 
challenge. Lehoux explores how the ancient historian may justify a realist rather than a relativist 
position, and I suggest that Lehoux’s historiography and philosophy of science are consistent 
only if we take his historiography, like his philosophy, to depend on a pragmatist theory of truth. 

 
Laws of Nature 
 
In his third chapter, “Law in Nature, Nature in Law,” Lehoux argues that the concept of a “law 
of nature” is not an invention of sixteenth- or early seventeenth-century natural philosophy as is 
generally supposed. The phrase itself, leges naturae or foedera naturae, occurs in Latin texts, 
and Lehoux analyzes passages from Lucretius’ De rerum natura and Vergil’s Georgics to 



What can we know?  24 
 

 

demonstrate that these authors not only include the phrase “law(s) of nature” but that they use it 
to denote strict regularity in nature, which Lehoux takes to be the concept’s essential content.  

Lehoux acknowledges that pure philology would not persuade many, perhaps most, 
philosophers of science that a law of nature is an ancient rather than a modern concept. An 
intellectual history is necessary, and it must respond to philosophical investigations of the 
concept. Before challenging Jane Ruby’s and J.R Milton’s accounts of what constitutes a natural 
law, Lehoux distills their and others’ criteria into two: 

 
(a) They should be specific statements that such-and-such is a law of nature (as opposed to 
vaguer statements that there just are some laws of nature), and 
(b) The x in “x is a law of nature” should be descriptive, explanatory, and preferably 
mathematical. (Lehoux 2012, 64) 

 
Lehoux notes that the first criterion, “the specificity criterion”, dismisses most of the ancient 
examples he has presented in the chapter. Lucretius and Vergil observe that nature, broadly 
conceived, behaves regularly, but they do not articulate specific laws. I would contend that one 
of the examples Lehoux presents might meet the specificity criterion. At De rerum natura 
6.906ff., Lucretius states that a law of nature is responsible for the attraction between magnets 
and iron, and he proceeds to explain the attraction by means of atomism. Yet, even if this case 
meets the first criterion, it does not meet the second. The law is descriptive, but what is 
explanatory is not the law of attraction but the atomism underlying it. Moreover, the law is 
manifestly not mathematical. 

Newton’s laws of motion customarily are taken to be archetypal cases of laws of nature, and 
Lehoux uses their notoriety to his advantage. He examines why it is that Newton’s laws are 
paradigmatic: “So what is significantly new in the Principia? There are three possible 
candidates: (1) Newton’s equivalence of axioms with laws: axiomata, SIVE leges motus. (2) The 
specificity of the phrase laws of motion. (3) The content of the laws themselves” (Lehoux 2012, 
68). The first candidate is a lexigraphical innovation, the second is philological, and the third 
concerns content. Lehoux maintains that what is essential to a law of nature is not lexigraphical 
or philological, for these properties are superficial. Instead, it is the content – which Lehoux 
takes to be strict regularity in nature – that marks a law. If one takes the content to be the only 
essential property of laws of nature, then one may find examples that are laws even if they lack 
the philological and lexigraphical features.  

This content-based approach allows Lehoux to bring Greek texts into the conversation. As 
Lehoux notes, only one reference to a “law of nature” exists in the Greek corpus. The opening of 
the Hippocratic text On Generation/On the Nature of the Child reads “law governs everything” 
(in Lehoux 2012, 57). For a law that is descriptive, explanatory, and mathematical, albeit not 
labeled “law,” Lehoux looks to Ptolemy’s models of planetary motion and, in particular, his 
account of planetary stations. Lehoux argues that Ptolemy’s account at Almagest 12.1, H450-
451, meets the content-based criterion no less than Newton’s laws. 



25  Feke 
 

 

It is true that Ptolemy never uses the phrase “law of nature,” but he does examine law, and the 
institution of the court of law, alongside his epistemological theory. In On the Kritêrion and 
Hêgemonikon, Ptolemy constructs an analogy juxtaposing judicial adjudication with the criterion 
of truth, the process by which a human being judges an object for the sake of knowing the truth. 
Although Lehoux addresses Ptolemy’s criterion in his fifth chapter, “The Embeddedness of 
Seeing” (see especially Lehoux 2012, 126-128), he does not address it in his discussion of 
Ptolemy’s (tentative) laws of nature. I hope to demonstrate that reference to On the Kritêrion, as 
well as the Harmonics, strengthens Lehoux’s argument, as it reintroduces the judicial metaphor. 
It is undeniable that Ptolemy does not discuss laws of nature per se but I will make the case that 
Ptolemy’s concepts of law and rational form, especially as manifested in the movements and 
apparent stations of celestial bodies, are analogous and that the metaphor afforded by the phrase 
“law of nature” is consonant with Ptolemy’s epistemology.  

In On the Kritêrion, Ptolemy delineates one-to-one correspondences between the processes of 
adjudication in the law court and in the soul: 

 
Criteria      In the Law Court In the Soul 
1. That being judged:    Act   What is 
2. That through which it is judged:  Presentation  Sense perception 
3. That which judges:    Chief magistrate Intellect 
4. That by which it is judged:   Law   Reason 
5. That for the sake of which it is judged: Social Harmony Truth 

 
In the judicial process, a magistrate brings a law to bear on an action in order to judge whether it 
accords with social harmony. In other words, the law is the means by which a magistrate passes 
judgment on an action. In the soul, the intellect judges an object by means of reason. As means 
by which an agent makes a judgment, law and reason are analogous. Where would the regularity 
in nature, such as Ptolemy’s account of planetary stations, reside in the epistemological schema? 
I would argue that it lies not in the schema itself but at its conclusion. It is not a component of 
the process of judgment; it is the result of the process, the complete, concluding judgment the 
intellect makes. At first glance it might seem that the regularity might be the object judged, but 
for Ptolemy this first category puts forward a problem to be solved, such as an object’s yet-to-be-
determined size or weight. In the case of planetary stations, the problem to be solved is the 
manner by which a planet gives the appearance of a station, and the solution, arrived at by way 
of the criterion, is the geometrical account of how the planet moves along its epicycle, as 
articulated at Almagest 12.1, H450-451. Thus far, Ptolemy’s account of planetary stations does 
not seem to correspond to a law. Only reason, the means by which the agent makes the judgment, 
is analogous to law. 

Reason, however, is not simply a property of human souls for Ptolemy. Acknowledging its 
broader, generic definition elucidates in what way Ptolemy’s account of planetary stations may 
indeed correspond to a law. In Harmonics 3.3 and 3.4 – transitioning from the study of 



What can we know?  26 
 

 

harmonics in music theory to psychology, astrology, and astronomy – Ptolemy defines reason as 
a cause that produces order and proportion in matter and movements. In Harmonics 3.3, he 
propounds a trichotomy of causes: “Now causes at the highest level fall into three kinds, one 
corresponding to nature and concerned only with being, one corresponding to reason and 
concerned only with being in a good way, and one corresponding to God, concerned with being 
in a good and eternal way.” Ptolemy divides reason into three subspecies: “For reason, in general 
and without qualification, is productive of order and proportion, while harmonic [reason], in 
particular, is [productive of them] in the class of what is heard, just as is imagistic [reason] in 
that of what is seen, and critical [reason] in that of what is thought” (Ptolemy Harmonics 3.3, 
D92, translation modified from Barker). In other words, reason produces a good form, order and 
proportion, in objects, whether they are audible, visible, or cognitive. 

The power, or capacity, of harmonia is one form of the cause corresponding to reason. It 
produces a harmonic form in or among objects. Ptolemy explains in Harmonics 3.4 that, 
although this power exists to some degree in all self-moving objects, it exists to the greatest 
extent in objects with a complete and rational nature (τελειοτέρας καὶ λογικωτέρας φύσεως). 
According to Ptolemy, three sets of objects have the most complete and rational nature and, 
moreover, display this nature in their movements. In addition to musical pitches, they are human 
souls and celestial bodies: 

 
These [movements], as we said, are those of things that are more complete and more 
rational in their natures (αὗται δέ εἰσιν αἱ τῶν τελειοτέρων, ὡς ἔφαμεν, καὶ λογικωτέρων τὰς 
φύσεις), as among the divine are [the movements] of the heavens, and among the mortal [the 
movements] of human souls, most particularly, since it is only to each of these mentioned 
that there belong not only the primary and most complete (τελειοτάτης) sort of movement, 
that in respect of place, but also the characteristic of being rational (λογικοῖς). (Ptolemy 
Harmonics 3.4, D95, translation modified from Barker) 

 
Among the most complete and rational of physical objects, celestial bodies display their rational 
nature in their movements. An account of planetary motion, therefore, is an account of their 
rational form. If one returns to On the Kritêrion and takes some liberty to interpret the judicial 
analogy as indicating that all reason – not only critical reason but also harmonic and imagistic – 
is analogous to law, then, I would suggest, an account of a rational form, celestial or otherwise, 
does correspond to a law. Ptolemy’s accounts of the rational movements of celestial bodies, 
including their stations, are analogous to laws, and one may justifiably consider them, 
metaphorically speaking, laws of nature. 
 
The Skeptical Challenge 

 
In the chapter “The Embeddedness of Seeing,” Lehoux characterizes Ptolemy’s and Galen’s 
theories of vision as responses to the so-called “Skeptical challenge.” Lehoux declares, “We will 



27  Feke 
 

 

see that both Ptolemy and Galen adopt identical strategies for meeting the Sceptical challenge, 
where they both put together detailed physical explanations of how seeing happens in the world, 
explanations that for them close off any potential inroads for the Sceptics” (Lehoux 2012, 107). 
It is important to examine in what way, if any, Ptolemy addresses skepticism. After all, Ptolemy 
does not explicitly discuss skepticism, as Galen does. The Pyrrhonist attack on the criterion of 
truth was robust in the second century, as Sextus Empiricus’ treatment of the subject attests, but 
when Ptolemy delineates his theory of cognition in On the Kritêrion, as well as in Harmonics 
1.1, he does not address skeptical challenges. A.A. Long agrees: 
 

No committed idealist or sceptic would be converted to materialism or empiricism by 
reading Ptolemy On the Criterion and Commanding Faculty. His essay not only omits any 
reference to Academic and Pyrrhonian attacks on the foundations of knowledge, it also 
avoids the slightest suggestion that any controversy attends an account of the criterion of 
truth. Never hinting at any of the battery of available arguments for or against scepticism, 
which were commonplace in his day, Ptolemy writes as if the only issue is to settle the 
relative criterial contributions of sense perception and intellect, from an implied basis of 
general agreement concerning human accessibility to how things really are. (Long 1989, 
153) 

 
If Ptolemy’s epistemological accounts make no reference to skepticism, in what way, if any, 
does his theory of vision respond to the Skeptical challenge? 

Lehoux characterizes Ptolemy’s theory of vision as a robust challenge to skepticism mainly, it 
seems, because it is a physical rather than a representational theory. It is not that a human being 
creates representations of the external world; rather, the external world impresses itself upon a 
human being through the capacity of sense perception and its concomitant faculty of phantasia, 
the medium that transmits sense impressions to the intellect. Lehoux implies that the continuous, 
unbroken physical chain of contact from external object, through the senses and phantasia, to the 
intellect in Ptolemy’s theory bolsters it against skeptical assaults (Lehoux 2012, 127-129). It is 
important to note that Ptolemy’s epistemology is informed by several philosophical traditions – 
including the Platonic, Aristotelian, and Stoic – but the fundamentals of his criterion of truth, in 
particular the relationships among sense perception, phantasia, and the intellect, derive from 
Aristotle’s epistemology.  

While Ptolemy does not explicitly address skeptical attacks, Aristotle does. In Metaphysics 
4.5, Aristotle examines pre-Socratic challenges to the possibility of knowledge, and he argues 
that previous philosophers have fallen victim to a fatal mistake. They have identified being with 
the perceptual, external objects with appearances. Emphasizing the distinctions between the 
potential and actual, quality and quantity, and special and common sensibles – properties 
particular to one sense or perceptible by many senses – Aristotle divorces being and the 
perceptual and he affirms that it is indeed possible to know what is true. The concept of special 
sensibles is especially significant here. Aristotle argues that the skeptical claim that an object 



What can we know?  28 
 

 

gives rise to contrary appearances at a given time is in fact false. When the intellect examines 
sense impressions, it can acknowledge that the senses have authority over their special sensibles 
and, consequently, it will not err when judging what is true. Aristotle declares, “but concerning 
color sight [is authoritative], not taste, and concerning flavor taste, not sight; each of which never 
says at the same time concerning the same object that it is at once this way and not this way” 
(Aristotle Metaphysics 4.5.1010b16-19; cf. Aristotle De Anima 418a11-14). Because special 
sensibles do not give rise to conflicting appearances, they undermine the Skeptical challenge. 

In On the Kritêrion, Ptolemy appropriates the theory of special sensibles and he affirms, 
“Certainly, on its own each of the faculties naturally tells the truth whenever it is concerned only 
with its own proper object…” (La16, translation modified from Liverpool/Manchester Seminar 
on Ancient Philosophy). The truth of special sensibles is foundational to Ptolemy’s 
epistemology. Because the senses transmit accurate impressions of external objects, knowledge 
is possible. Again, Ptolemy does not address skeptical attacks here, when describing special 
sensibles, or elsewhere, but because Aristotle articulates his theory of special sensibles as a 
defense against skepticism, one could argue that Ptolemy’s epistemology responds to the 
Skeptical challenge by extension from Aristotle. Although Ptolemy does not address skeptical 
attacks, aspects of his epistemological theory derive from accounts that do. 

 
Eikos Muthos: An Impediment to Epistemic Progress? 
 
Lehoux not only provides an expansive portrait of Roman science, but he also reflects on the 
nature of historical study and its relevance to the philosophy of science. Concerning the former, 
Lehoux examines the degree to which the historian can understand ancient scientific thought. 
After all, Lehoux’s portrait of Roman science is complex. Intellectual, social, and cultural factors 
contributed to the production of Roman scientific texts. How is it, then, that a historian can 
analyze and interpret, in the actors’ own terms, Ptolemy’s models of planetary motion, Galen’s 
pneumatic theory, and the “fact” that garlic is antipathetic to magnets? A pessimist might argue 
for complete incommensurability, that these theories are untranslatable to the modern 
perspective. More optimistically, a historian might suppose that through prolonged engagement 
with these texts she can become increasingly familiar with the several causes of ancient science, 
that she may slowly but surely gain understanding of the network of contributing factors, and 
that, therefore, she has the ability to construct an increasingly accurate portrait of ancient 
thought. Lehoux characterizes this impression as follows:  
 

At the softer end, approximation, the historian or ethnologist can argue that long-term 
exposure to another culture can give one ways of seeing its terms, concepts, and categories 
that allow for at least proximate (and presumably also improvable) translation, and so over 
time I can come to find ways of understanding and explaining Galenic pneuma that do not 
necessarily imply that I have found some neutral third ground from which to view both 



29  Feke 
 

 

Galen’s world and my own and through which to shuttle material back and forth. (Lehoux 
2012, 231) 

 
Lehoux acknowledges that, at best, a historical study approximates the truth. I would add that, if 
we admit progress in historical study, it is asymptotic. Even with increasing familiarity, it 
remains impossible to know for certain what a historical actor intended by a text. While this 
uncertainty is not a concern for the critical theorist, it marks the limit of inquiry for the 
intellectual historian.  

I would like to suggest that this inherent uncertainty marks the history of science as an eikos 
muthos, a likely story. For an analogue, one may look to Plato’s distinction between certain and 
likely accounts. In the Timaeus, Plato’s principal interlocutor affirms that an account of the 
sensible realm, as opposed to the intelligible, is limited to a likely story. Timaeus prepares 
Socrates for his cosmological account with the following warning: 

 
Don’t be surprised then, Socrates, if it turns out repeatedly that we won’t be able to give 
accounts concerning a great many subjects – on gods and the coming to be of the universe – 
that are completely and perfectly consistent and accurate. Instead, if we can come up with 
[accounts] no less likely than any, we ought to be content, keeping in mind that both I, the 
speaker, and you, the judges, are only human in nature. So we should accept the likely tale 
on these matters. It behooves us not to look for anything beyond this. (Plato Timaeus 29c-d, 
translation modified from Zeyl; cf. 59c6 and 68d2) 

 
According to Plato, an account of the sensible realm is at most probable. Similarly, the historian 
may at most present a likely account of ancient scientific thought, but of what, then, would the 
historian have certainty? 

Lehoux argues for the certainty of epistemic progress. Again, Lehoux does not limit history to 
the examination of historical texts. He applies the historical lens to contemporary, twenty-first-
century sciences, and he asks, What position must the historian, or the historically informed 
philosopher, take on the debate over scientific realism? A significant hurdle to the realist is the 
pessimistic induction, the argument that because so many past “successful” theories have since 
been proven false, the success of current theories does not guarantee their truth, as in the future 
they, too, will likely be proven false. Lehoux takes the pessimistic induction as a serious worry 
for the realist, and he seems to formulate his position in response. He affirms that the philosopher 
must not privilege modern scientific theories simply because of their modernity. The philosopher 
may desire a transhistorical perspective from which to judge the relative truth of scientific 
theories, and the realist may desire some transhistorical criteria by which to judge the relative 
truth of scientific theories, but it is impossible to remove oneself from one’s network of 
contributing causes – the intellectual, social, and cultural conditions, and prejudices, of 
contemporary science.  



What can we know?  30 
 

 

Lehoux implies that one may approach, although not assume, this transhistorical perspective 
by adopting a consistent, singular, historically informed methodology. In order to evaluate the 
relative truths of scientific claims, one must employ the same methodology when examining 
Roman and twenty-first-century scientific texts. The fear is that this approach will yield 
unadulterated relativism, and, indeed, Lehoux’s realism seems to fight a constant battle with 
relativism. In the final chapter, “Worlds Given, Worlds Made,” Lehoux ultimately gestures 
toward a pragmatist theory of truth. He quotes William James, one of the earliest proponents of 
pragmatism: “True ideas are those that we can assimilate, validate, corroborate and verify. 
False ideas are those that we cannot…. The truth of an idea is not a stagnant property inherent in 
it. Truth happens to an idea. It becomes true, is made true by events. Its verity is in fact an event, 
a process: the process namely of its verifying itself, its veri-fication” (in Lehoux 2012, 236; 
emphasis James’). Because a transhistorical perspective is impossible to achieve, Lehoux adopts 
an epistemology that affirms the situatedness of science. It seems that, for Lehoux, the only 
robust theory of truth is a pragmatist one. 

Lehoux uses pragmatism to make a case for scientific realism. He contends that, with a 
pragmatist theory of truth, it is possible to accept epistemic progress without biasing modernity. 
He explains as follows: 

 
Although a Jamesian theory would seem to want to conclude that pneuma and sympathy 
were once true, the fact that they are no longer true is not just a function of our adoption of a 
different worldview, but instead a function of the nontrivial fact that in the intervening 2,000 
years we think we have had experiences that disprove them or render them useless or 
superfluous. Magnetism has built around itself a host of tests and theories that were not part 
of the verification process available to the Romans, and so magnets-as-sympathetic have 
been shown to be false. This fact may also allow for a (qualified) notion of something like 
epistemic progress, without the normally attendant triumphalism. (Lehoux 2012, 237) 

 
When asserting epistemic progress, it is not necessary to privilege modernity. The passage of 
time is not the crucial factor but, rather, the accumulation of methods of justification. One need 
not assume a relativist position and judge the antipathy of garlic and magnets to be true for the 
Romans but false for us. According to Lehoux’s realism, one may assert that antipathy is simply 
false, and he may do so because in the intervening period of time human beings have developed 
means of verification that were unavailable to the Romans. 

It seems that a crucial point for Lehoux’s argument is that it is not the case that the types of 
verification performed in the Roman period and the twenty-first century are simply different in 
kind. If it were, then the historian-philosopher would have no means to compare the relative 
merits of the two systems, and relativism would win its battle with realism. The question, then, is 
what criteria establish the superiority of the modern systems of justification over the ancient. 
Lehoux is unclear on this matter, but he seems to imply two: (1) the modern system is larger than 
the ancient, and (2) the modern is more rigorous than the ancient.  



31  Feke 
 

 

Concerning the first, Lehoux observes that the number of methods of verification has 
increased over time, and he implies that this increase, in and of itself, establishes epistemic 
progress. A greater number of methods, however, would not establish the superiority, or success, 
of modern methods over the ancient. It is easy to imagine many unsuccessful methods 
juxtaposed with a few successful ones. Lehoux’s second implied criterion, the comparative rigor 
of the methods, is necessary to determine their relative merits. Lehoux gestures toward this 
criterion when characterizing the type of truth pragmatism allows: “But if, for the pragmatist, 
verifiability leads to variability, what kind of truth is that? The pragmatist answer is: the only 
kind we have. Truth is a stamp of approval that we give things as a way of saying that they meet 
certain – and most rigorous – criteria” (Lehoux 2012, 237; emphasis Lehoux’s). Affirming 
epistemic progress – and the justifiability of considering certain ancient theories false and 
twenty-first-century theories true – Lehoux implies that today’s methods of verification are more 
rigorous than the ancient.  

While I do not know a single person who would disagree with this assessment, it requires 
justification. Lehoux seeks a criterion that is transhistorically indisputable, one that Ptolemy, 
Galen, or any other historical actor would accept, but would Ptolemy agree that astronomy today 
is more rigorous than in the second century? Would Galen concede the superiority of twenty-first 
century medicine? I believe that they would, but, this speculation aside, Lehoux’s historiography 
could undermine his attempt to establish epistemic progress. If the historical enterprise is at most 
an eikos muthos, an approximate, albeit likely, account of the past, how can the historian-
philosopher justifiably and definitively judge twenty-first-century systems of justification to be 
superior to the ancient ones? Perhaps Lehoux’s pragmatism resolves the issue. The historian 
cannot know for certain that her account of Roman scientific theories is accurate, but employing 
the most rigorous criteria in the history and philosophy of science, one may, following James, 
validate, corroborate and verify that twenty-first-century science stands as an improvement on 
ancient science. 

 
Conclusion 
 
Lehoux’s What Did the Romans Know? (2012) is an innovative and commendable exercise at the 
intersection of ancient history and the philosophy of science. I have attempted to reinforce 
significant portions of his argument against potential challenges, historical and philosophical, 
and I hope that Lehoux’s monograph will inspire ancient historians and philosophers alike to 
consider the consequences of each other’s disciplines for their studies. 

 
 
 
 
 
 



What can we know?  32 
 

 

Works Cited 
 
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(repr. 1967). 
 
–––. 1970. Aristotle’s metaphysics, 2 vols. Trans. Ross, W.D.  Oxford: Clarendon Press, 1924 

(repr. 1970 [of 1953 corr. edn.]). 
 

Barker, Andrew. 1989. Greek Musical Writings, 2 vols., Cambridge: Cambridge University 
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