












































[Expositions 6.2 (2012) 10-14]  Expositions (online) ISSN: 1747–5376 

Shaping Worldviews: Contextualizing Roman Science 
  
Elizabeth A. Hamm 
Saint Mary’s College of California 

 
 

Daryn Lehoux’s comprehensive and thoughtful work, What did the Romans Know? An Inquiry 
into Science and Worldmaking (2012) emphasizes just how difficult the task of studying a world 
so foreign to our own can be for the historian. In addressing the question raised in his title, 
Lehoux describes the social, political, and religious context in which scientific ideas were 
developed in the Roman world between the first century BCE and the second century CE. With a 
sound understanding of Roman natural philosophy and a touch of humor, Lehoux’s work 
investigates ideas fundamental to the history and philosophy of science.  

While the Romans are at the heart of this study, the questions examined by Lehoux extend 
beyond the geographical and chronological parameters of the book, making it a welcome 
contribution to the history of science. It is only by stepping out of our modern way of seeing the 
world, Lehoux argues, that we can begin to understand how the ancients approached, 
comprehended, and rationalized the world around them. Roman science – complete with 
divination, astrology, and numerology – appears strange, but Lehoux contends that while these 
concepts are foreign, “their difficulty lies not in their weirdness but in the ancient claims as to 
how good the evidence for them is” (Lehoux 2012, 14). The importance of understanding the 
context in which scientific ideas flourish is imperative for all historians of science, and Lehoux 
demonstrates that ideas about the physical world around us, which modern readers might take for 
granted, cannot be assumed about the ancient scientist.  

Lehoux’s work is marked by judicious use of evidence and a careful analysis of his subject. 
Organizing his ideas thematically, he begins by addressing the relationship between nature and 
laws in chapters two and three. Lehoux explores the Romans’ understanding of the role of gods 
in the physical world and the interrelation between judicial laws and nature. Taking Cicero as a 
case study, Lehoux demonstrates how Cicero’s view of the natural world influenced his 
understanding of law: Cicero argues that just social interactions between people are natural and 
that these types of interactions form the basis for civil law (Lehoux 2012, 31). Alternatively, the 
Romans’ understanding of law influenced the way they viewed the natural world. Lehoux uses as 
another example Ptolemy’s findings on planetary stations – the point at which a planet, 
beginning or ending a retrograde pass, appears to stop in the sky – to illustrate a law ascribed to 
the natural world. This demonstrates that laws of nature do not make their first appearance in 
early modern science as is often assumed, but that they can be found in ancient science. In 
chapter four, “Epistemology and Judicial Rhetoric,” Lehoux explores the concept of the observer 
as a judicial witness. Viewing the scientific observer in this light raised questions for Roman 
natural philosophers about the credibility of the witness, who counts as a witness, and the use of 
the reader as a witness. 



11  Hamm 
 

 

While the first three chapters, all of which feature the relationship between nature and law, are 
closely linked, in chapter five, “The Embeddedness of Seeing,” the author turns his attention to 
the visual theories proposed by Galen and Ptolemy. Lehoux explores how both authors – 
Ptolemy from a mathematical perspective and Galen from a medical perspective – used the same 
principle in their visual theories: namely, that things similar to each other are able to influence 
each other, a concept that Lehoux refers to as the law of “like affects like.” This principle is 
assumed by both authors, but never justified. Lehoux argues that this law, “like affects like,” is 
an example of a preconceived idea about the world that did not require explanation. In 
formulating ideas about the natural world, the Romans wove together observations and 
assumptions about how the natural world works, but what they saw when they looked at the 
world and what they understood about the world are not the same as what the modern reader sees 
and understands.  

Lehoux’s most poignant ideas come through in his discussion of garlic and magnets in chapter 
six, “The Trouble with Taxa,” which he states was the kernel for this project. It is in this chapter 
that the claim that the Romans had different facts than what we have today, an idea that he 
alludes to in the introduction, resonates most clearly for the reader. According to Plutarch, 
Ptolemy, and others, rubbing a magnet with garlic neutralized its power of magnetism. Lehoux 
explains that this idea, completely baffling to modern readers, was treated as a fact in the Roman 
world. Neither Plutarch nor Pliny needed to test such a theory, in the same way that most modern 
readers will not feel the need to test whether garlic will have any impact on magnets. We take for 
granted that garlic has no effect on a magnet, in the same way that many Romans took for 
granted that garlic does have a disabling effect on a magnet. (As an aside, in the midst of reading 
chapter six, I found myself in my kitchen rubbing garlic on refrigerator magnets – for the record, 
I observed the magnets to behave the same before and after their garlic encounter.) While there 
are several examples that buttress Lehoux’s argument that Roman science developed in a distant 
world, complete with its own governing rules, underlying truths, and facts, this example is the 
most effective at demonstrating the strangeness of Roman science to the modern reader.  

Models and theories not only offer explanations, but they also influence the way we view the 
world. In chapters seven and eight Lehoux explores how allowing different entities – a divine 
being, astrology, or sympathy – into an explanation changes how the world works, what we 
observe, and how we understand it. Additionally, he examines the belief that a working theory 
that adequately explains observed phenomenon can also explain confounding observations in an 
unrelated branch of science. These symmetrical explanations, as Lehoux calls them, illustrate the 
ancients’ view of a world that worked according to underlying principles that transcended 
specific fields.  

While Lehoux’s thematic approach is effective, the nuances of the different theories and the 
processes of constructing theories are sometimes lost. The principles, observations, and modes of 
explanation are unique to each historical actor; moreover they are not stagnant but regularly 
changing. Consequently the historian must understand the subtle details of the individual theories 
and how they change. A single example might serve to illustrate the point: one of Ptolemy’s 



Shaping Worldviews  12 
 

 

arguments in the Almagest for the circular motion of the heavens is that the sizes and distances of 
the stars do not appear to vary over the course of a revolution of the celestial sphere. He argues 
that the distances of the stars from the Earth must therefore be constant.1 Ptolemy says: 

 
For the apparent increase in their sizes at the horizons is caused, not by a decrease in their 
distances, but by the exhalations of moisture surrounding the earth being interposed 
between the place from which we observe and the heavenly bodies, just as objects placed in 
water appear bigger than they are, and the lower they sink, the bigger they appear. 
(Ptolemy 1998, 39)  

 
Ptolemy is referring to the occurrence of the Sun and Moon appearing larger when viewed at the 
horizon. He contends that this phenomenon, which is often referred to as the Moon illusion, is 
due to the median through which we view the Sun or Moon: namely, the air and the moisture in 
it. It is clear that he does not think the Moon is closer to the Earth when we view it near the 
horizon and further from the Earth when we view it near the zenith. Instead, he says that the 
Moon appears to increase in size when viewed near the horizon due to (what seems to be) 
refraction. While this explanation at first seems sensible to Ptolemy, he later provides a different 
account of the observation: that the angular diameter of the Moon is same when measured at the 
horizon and zenith.  

In the Optics, Ptolemy attributes this phenomenon to a psychological effect. In Book III of the 
Optics, he accounts for the Moon illusion: 

 
Generally speaking, in fact, when a visual ray falls upon visible objects in a way other than 
is inherent to it by nature and custom, it perceives less clearly all the characteristics 
belonging to them. So too, its perception of the distances it apprehends will be diminished. 
This seems to be the reason why, among celestial objects that subtend equal visual angles, 
those that lie near the zenith appear smaller, whereas those that lie near the horizon are seen 
in another way that accords with custom. Things that are high up seem smaller than usual 
and are seen with difficulty. (Ptolemy 1996, 151)  

 
Ptolemy explains that celestial bodies that subtend equal angles, and are consequently the same 
size, appear bigger when viewed near the horizon due to the way the visual rays from the eye fall 
on the object. The Moon would be the same size when viewed near the zenith or the horizon; 
however, the observer would think the Moon appears to be larger nearer to the horizon. Ptolemy 
argues that the eye must gaze up to see the object, and the visual ray falls upon the object in a 
way to which it is not accustomed. When the same celestial object is viewed near the horizon 
then the visual ray makes contact with the object in a way that is “inherent to it by nature and 
custom” (Ptolemy 1996, 151).  

The different explanations of the Moon illusion in the Almagest and the Optics demonstrate 
Ptolemy’s evolving theories on optics as applied to astronomy. At first he explains an 



13  Hamm 
 

 

inexplicable phenomenon, that the Moon appears larger when viewed near the horizon, using 
refraction. Later he revised his account, presumably after observing that the Moon in fact appears 
to be the same size when viewed near the horizon or zenith, and he replaced his theories this time 
relying on a different theory to explain the phenomena, or in this case, the lack thereof. 
Consequently, both what the observer saw and how those observations were explained were 
shifting for Ptolemy. We can see from this example that there was not one Roman mindset to 
understand. Rather, each author had a different approach to explaining the world, and these 
approaches were often evolving. Lehoux acknowledges this and he does not endeavor to explain 
the scientific theories of all of the characters he examines; in fact he says that he will only 
examine the most significant of the interconnections, so in some ways this critique may be unfair 
(Lehoux 2012, 2). Nevertheless, the reader needs to be attuned to the fact that there is not a 
single web of knowledge, but many webs of knowledge, and that historical actors make sense of 
the world in very different, and constantly shifting, ways.  

In the final chapters of the book Lehoux changes the lens he uses to examine the ancient 
world by situating Roman science within philosophy of science debates on realism. He raises 
two main questions: (1) Can a historian be a realist and offer a fair portrayal of ancient science? 
And, (2) How does the criteria for realism hold up against ancient scientific theories? 
Concerning the first question, Lehoux analyzes how the historian can offer a fair consideration of 
ancient science, but at the same time believe that our modern scientific theories are 
approximately true. This idea is closely tied to the second question, which asks how the 
philosopher of science should approach ancient science. Lehoux examines a Hippocratric work, 
On Ancient Medicine, in which the author states that the accuracy of current medical theories 
demonstrates that they are “rightly and truly uncovered, and not the product of accident” 
(Lehoux 2012, 205).2 This idea is similar to Hillary Putnam’s famous miracle argument: “The 
positive argument for realism is that it is the only philosophy that doesn’t make the success of 
science a miracle” (Putnam 1975, 73; see Lehoux 2012, 204). The similarity of these ideas, one 
an observation by a Roman author and the other a weighty argument in the philosophy of 
science, leads Lehoux into an exploration of what separates modern views that our science is 
approximately true from the Romans’ confidence in the truth of their own theories. He shows 
that some of the theories proposed by authors such as Galen and Ptolemy fare surprisingly well 
against criteria of what constitutes a scientific theory that is viable, mature, and approximately 
true. In the end, Lehoux sketches out a broad strategy for the historian/realist where modern 
scientific models are viewed with a pragmatic theory of truth and a coherence-based 
epistemology. That is to say that only the parts of our theories that are verifiable, testable, and 
cohere should be considered to be true, or approximately true. While Lehoux’s discussion of the 
place of Roman science in modern philosophical debates represents a departure from the themes 
covered in the rest of the book, the last two chapters nevertheless offer much food for thought for 
historians and philosophers alike.  

Science does not take place in a vacuum. Underlying ideas, many of which may be so deeply 
rooted that they are unknown to the scientists, play an essential role in the development of 



Shaping Worldviews  14 
 

 

theories. The historian’s role is not to condemn ancient ideas as silly or naïve, but to make sense 
of those ideas with the larger social, political, and religious context in mind. Lehoux examines 
the title question, “What did the Romans know?” from almost every angle, revealing a Roman 
world more intricate and intellectually complex than is often assumed. His fresh writing style 
holds the reader’s attention and his peppering of modern references keeps the reader on her toes. 
This is a thought-provoking work and one that explores many critical questions for the historian 
and philosopher of ancient science. 

 
 

Notes 
 

1. According to Ptolemy: “To sum up, if one assumes any motion whatever, except 
spherical, for the heavenly bodies, it necessarily follows that their distances, measured 
from the earth upwards, must vary, wherever and however one supposes the earth itself to 
be situated. Hence the sizes and mutual distances of the stars must appear to vary for the 
same observers during the course of each revolution, since at one time they must be at 
greater distance, at another at a lesser. Yet we see that no such variation occurs” (Ptolemy 
1998, 39). 

 
2. Lehoux includes both the original Greek text and an English translation. 

 
 
Works Cited 
 

Lehoux, Daryn. 2012. What Did the Romans Know? An Inquiry into Science and 
Worldmaking. Chicago: University of Chicago Press. 

 
Ptolemy. 1996. Ptolemy’s Theory of Visual Perception: An English Translation of the Optics 

With Introduction and Commentary. Trans. and commentary by Mark A Smith. 
Philadelphia: American Philosophical Society.  

 
–––. 1998. Ptolemy’s Almagest. Trans. by G. J. Toomer. Foreword by Owen Gingerich. 

Princeton, NJ: Princeton University Press. 
 
Putnam, Hilary. 1975. Mathematics, Matter, and Method. Cambridge: Cambridge University 

Press.  
 
 


