Monday, March 31, 2014


Alan C. Bowen, Simplicius on the Planets and their Motions: In Defense of a Heresy. Philosophia antiqua, 133. Leiden; Boston: Brill, 2013. Pp. xviii, 329. ISBN 9789004227088. $175.00.

Reviewed by Nathan Sidoli, Waseda University (

Version at BMCR home site


This book presents Bowen's translation and interpretation of a famous, and notoriously difficult, passage of Simplicius' Commentary on Aristotle's On The Heavens ('In de caelo'), namely the digression on the early history of Greek mathematical astronomy, In de caelo 2.12, along with the two forgoing sections, 2.10 and 11, which Bowen includes in order to set 2.12 in its proper context. As well as providing a careful reading of these passages, the book provides us with an argument that Simplicius' treatise must be understood in the context of contemporary philosophical arguments and is not unproblematically useful as evidence for the early history of Greek astronomy.

The work begins with an introduction that situates Simplicius' Commentary as a defense of aspects of Aristotle's thought in the face of arguments advanced by John Philoponus against the divinity and eternity of the heavens, and concludes with a discussion of Simplicius' sources for the history of astronomy and the claim that there is no way to objectively use Simplicius' text as evidence for the early history of Greek astronomy (pp. 3-93). This is followed by the translation (pp. 94-177), which is in turn followed by the commentaries (pp. 181-298). The commentaries – which are variously philological, technical, philosophical, and historiographical – are referred to by footnotes in the translation, and each commentary is in turn referenced back to its footnote. There are also two sections of diagrams to help readers follow the train of thought, although there are no diagrams in the manuscript sources for Simplicius' Commentary (pp. 22-5, 181-97).

The sections of Simplicius' Commentary covered in this book are some of the most frequently studied passages in the treatise. The reason for this has to do with Simplicius' treatment, in In de caelo 2.12, of a research program involving homocentric spheres that was apparently developed by mathematicians such as Eudoxus and Callippus during the 4th century BCE. Starting in the early part of the 20th century, historians of astronomy have attempted to use these passages to (re)construct an episode in the early history of the Greek effort to model astronomical phenomena using homocentric spheres. This type of scholarship involves massaging and correcting the text in various ways, proposing different ways of parsing Simplicius' quotations of his sources, and developing mathematical models that can predict various planetary phenomena. Some of the issues with this approach are that the text allows for multiple readings and that it has never been entirely certain what set of phenomena, or data, the classical mathematicians were attempting to explain.

The core of Bowen's argument is that this way of reading these passages is neither useful, nor historically sound. Instead, he argues that we have to understand Simplicius' treatment of the theory of homocentric spheres as a digression within a broader set of discussions meant to address arguments advanced by Philoponus. Essentially, Philoponus, as a Christian trained in late-ancient Platonic philosophy, had argued that Aristotle must have been wrong about the eternity and divinity of the heavens – and in particular in his claim that the heavens are composed of the special element, aether. Philoponus claimed that Aristotle must have been misguided in his belief that the heavens are made of an element whose nature is such that it always revolves regularly around its own center, because such a position was clearly contradicted by the more recent work of mathematicians, which had culminated in the Almagest of Claudius Ptolemy. These arguments put Simplicius in the awkward position of having to admit that, although Aristotle was wrong about homocentric spheres, there is still a sense in which he was right about the nature of aether – that is, even in Ptolemy's theories, aether can be described as rotating regularly about a center, although this center is often not the center of the body, or sphere, in question. Furthermore, Simplicius claims that Aristotle was right to follow the lead of the mathematicians, since this is all that philosophers can do before there is a sound physical theory on the basis of which mathematicians could derive correct models of the heavenly bodies.1 On these grounds, he makes a case that his contemporaries are right to follow the work of later mathematicians, even where this disagrees with Aristotle – indeed, Simplicius himself accepts Ptolemy's models, while admitting that they in turn may later themselves be found wanting. In all of this, Simplicius presents a rather fanciful reading of Aristotle's On the Heavens in order to preserve this treatise as a vital part of the sacred curriculum of Platonic philosophy, despite its glaring discrepancies with contemporary beliefs about the nature of the heavens.

Although In de caelo 2.12 has been translated into English a number of times, and 2.10 and 11 are both included in Mueller's translation,2 Bowen's new translation is a useful contribution to our understanding of the treatise. For one thing, the text is often rather involved, so it will be valuable to scholars to be able to compare the places where Bowen's reading disagrees with Mueller's. Furthermore, Bowen has checked his reading of the text against the indirect tradition in the form of Latin translations of parts of the commentary made by Grosseteste and Moerbeke, which were, in turn, based on Greek sources that are different from ours. Hence, this translation is also an advance over Bowen's own previous translation of these sections.3 Furthermore, Bowen's detailed commentaries help the reader navigate the sometimes labyrinthine course of Simplicius' thought. Nevertheless, as Bowen himself says, the primary reason for giving a full translation and commentary is that it allows him to separate all the interpretive details of reading this text from the main thrust of his argument, which is that the text must be read in light of late Athenian Platonism (pp. 15-16).

There are a number of longer commentaries, in which Bowen sets out his own views on the history of Greek astronomy and its (re)construction by both ancient and modern scholars, but here I will discuss only one of these, in which Bowen argues that there is no compelling evidence that Greeks of the 4th and 3rd centuries BCE were aware of planetary retrogradation (pp. 230-48). Initially he argues only that it cannot be proven that fourth-century Greeks knew of the detailed phenomenon of retrogradation on the basis of contemporary documents, which is strictly true, but he then later goes on to claim specifically that awareness of stations and retrogradation entered the Greek sphere from Mesopotamia in the late 2nd or early 1st century BCE (p. 298). In order to arrive at this position, Bowen applies the fairly strict historiographical principle that nothing that later authors say about earlier authors can be accepted if it is not also supported by independent documents from the reported period. I call this principle 'strict' because none of the technical sources of early planetary theory survive, so that for contemporary sources we are forced to rely on the writings of philosophers, poets, and others whose statements about planetary phenomena and theories are plagued with a certain vagueness of language, or understanding, or both. From these writings we can only be sure that fourth-century Greeks were aware that (1) the planets meander (pp. 233, 241), that (2) Venus and Mercury are sometimes before, and sometimes behind, the sun (p. 234, 241), and that (3) at least some of these Greeks believed that (2) happens because Venus and Mercury are sometimes overtaken by the sun like runners in a race (p. 237, 243). At stake is the question of what kinds of observations, or data, classical theorists had at their disposal when they thought about modeling the motions of the planets. It seems to me that there is a range of possibilities. At one extreme is the possibility that classical Greeks were making and preserving continuous runs of carefully dated and systematically recorded observations, and hence knew rather precisely the phenomena of planetary stations and retrogradations. Although in the past views more or less equivalent to this position have been held, it is now seen as unlikely to most historians. Bowen's position, that the fourth-century Greeks were completely unaware of retrogradation, however, seems to me another extreme. Once it was realized that Venus is sometimes before, and sometimes behind, the sun in its path through the stars, it would take only a small number of crude observations to realize that it must be at least stopping, if not, indeed, retrograding, with respect to the fixed stars. Since consideration of the well-attested parapegmata would make it clear that the sun is moving through the fixed stars at a fairly regular pace, one would only have to notice the regular, and significant, difference in intervals from evening appearances to morning appearances, as opposed to from morning appearances to evening appearances, and put this together with a very rough measure of elongation, to realize that, in reference to the star calendar of the paragemata, it is natural to think of Venus as moving, for a short while, in the opposite direction from the sun when it goes from eastern appearance to western appearance, and as continuously in the same direction as the sun when it goes from western appearance to eastern appearance.4 In order to hold that this phenomenon was completely unknown, we would have to believe that fourth-century Greeks were almost completely unconcerned with planetary phenomena. It seems to me that there are many possibilities between these two extremes, many of which involve considering that the early Greek theorists were aware of retrogradations at least as general phenomena, if perhaps not as a precisely recorded behavior. Indeed, it is hard to imagine what could have been the point of producing mathematical models at all if the only thing that they were meant to show was that the planets meandered. Nevertheless, Bowen's point that the sources are unclear about precisely what phenomena the early theorists were trying to model is well taken, even if his insinuation that those who believe the early Greeks knew about retrogradation are inebriated may be taking the point too far (pp. 231, 247).

An important lesson from this book is Bowen's emphasis of the extent to which Simplicius' account of early Greek astronomy has shaped what we think we know about the history of Greek astronomy. Whether or not a reader agrees with all of Bowen's arguments, his general point that Simplicius was almost certainly rereading his own understanding of planetary theory into previous thinkers, who themselves may have had very different sets of concerns, is certainly sound. Simplicius himself was centuries removed from the theorists whose work he discusses, and his sources treated the history of the mathematical sciences using methods that are not well known to us, but which may well have involved speculative (re)construction. Hence, we cannot read Simplicius' historical account as a straightforward attempt to relate the historical facts and conditions of the fourth-century theorists. Whatever historical information Simplicius may be including, or obscuring, in his account, his primary purpose was to address issues in a contemporary philosophical debate about the nature of the heavens, not present a detailed historical understanding of homocentric modeling.

This book is a careful study of Simplicius' In de caelo 2.10-12 in the context of challenges to late-ancient Platonism raised by John Philoponus. It will be valuable to scholars interested in the efforts of the Athenian Platonists to create a synthesis of the thought of Plato, Aristotle and Ptolemy, in the history of ancient Greek astronomy and its sources, and in the historiography of early science.


1.   It should be noted that by a physical theory that could serve as the basis of a correct mathematical model of the heavens, Simplicius meant a physical theory in the ancient sense – that is, one involving an articulation of the essential nature of the objects involved – not a mathematization of the motions of bodies and forces – as was developed in the early modern period, when astronomy was finally set on a physical foundation.
2.   I. Mueller, Simplicius, On Aristotle's On The Heavens 2.10-14 (Ithaca: Cornell University Press, 2005).
3.   A. Bowen, 'Simplicius' Commentary on Aristotle's De caelo 2.10-12: An Annotated Translation', SCIAMVS 4 (2003), 23-58 and 9 (2008), 25-132.
4.   For a treatment of parapegmata, see D. Lehoux, Astronomy, Weather, and Calendars in the Ancient World. Cambridge, Cambridge University Press, 2007.

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