As the editors of this volume note in the preface, “[t]his volume is the first collection of scholarly articles in any modern language devoted to Aristotle’s De caelo.” The reason for this neglect is not difficult to discern. Aristotle’s De caelo comprises four books: two on the locomotion of the heavens and heavenly bodies and two on the locomotion of the terrestrial elements. It is, as David Ross once noted, “one of [Aristotle’s] boldest essays in a priori construction.” In fact, Aristotle turned out to be largely mistaken in his conclusions regarding both types of motion and the composition of astronomical and earthly bodies, though he seems to have been aware that, at least in the former case, the relative inaccessibility of these bodies to us put speculation regarding their scientific properties at the outer limit of our powers. For this reason, it has seemed to many that De caelo belongs among those works of Aristotle the conclusions of which have been so thoroughly demolished by the advance of empirical science that their study is fit only for the historically curious. And yet, it is undeniably thrilling to read Aristotle’s complex and resourceful reasoning from the starting-points he has adopted to the way things must be.
The essays in this volume focus for the most part on specific claims made in De caelo. They are now appearing roughly a decade after the various workshops in which they were presented. The essay by Johansen is the only one that reaches back to Plato’s Timaeus in any substantive way. The essay by Freudenthal is the only one that explores in detail part of the reception of Aristotelian cosmology. And the essay by Lennox is the only one to argue at length about the relation between De caelo and other works of Aristotle. The essays by Broadie, Hankinson, and Freudenthal are easily the most philosophically and (in the case of Freudenthal) historically interesting. The editors have provided an admirably extensive bibliography on the manuscripts, editions, translations, and books and articles on De caelo and have also had the good idea of putting this bibliography online for additions and corrections ( www.ircps.org/dir/bowen.htm). The authors and the titles of the essays are:
Thomas K. Johansen, “From Plato’s Timaeus to Aristotle’s De caelo : The Case of the Missing World Soul’; Sarah Broadie, “The Possibilities of Being and Not-Being in De caelo 1.11-12”; Robert Bolton, “Two Standards for Inquiry in Aristotle’s De caelo ”; R.J. Hankinson, “Natural, Unnatural, and Preternatural Motions: Contrariety and the Argument for the Elements in De caelo 1.2-4”; Mohan Matthen, “Why Does the Earth Move to the Center? An Examination of Some Explanatory Strategies in Aristotle’s Cosmology”; Mary Louise Gill, “The Theory of the Elements in De caelo 3 and 4”; Pierre Pellegrin, “The Argument for the Sphericity of the Universe in Aristotle’s De caelo : Astronomy and Physics”; James G. Lennox, “ De caelo 2.2 and Its Debt to the De incessu animalium”; Mariska E.M.P.J. Leunissen, “Why Stars Have No Feet: Explanation and Teleology in Aristotle’s Cosmology”; Gad Freudenthal, “The Astrologization of the Aristotelian Cosmos: Celestial Influences on the Sublunary World in Aristotle, Alexander of Aphrodisias, and Averroes”.
Johansen in his essay contrasts the cosmology of Plato’s Timaeus and Aristotle’s De caelo on the role of soul. As Johansen notes, although Aristotle abandoned a single world soul employed by Plato to account for the orderliness of this universe, he is far from dispensing with psychic principles in his cosmology. In De caelo, the outermost sphere of the heavens must be ensouled as well as the planets, in order to account for their circular motion in imitation of the blissful life of the unmoved mover. Thus, the principle of teleological causation drives a central hypothesis of celestial locomotion. Unlike Plato, however, the animated heavens, for Aristotle, do not provide an ethical model for human life. As Johansen explains, however, the specific topics in Plato’s comprehensive world view expressed in Timaeus are, for Aristotle, apportioned out among a number of different works, and even different sciences, such that Aristotle in fact endorses the imitation of the divine life in Nicomachean Ethics, though not in De caelo.
Broadie examines Aristotle’s argument in De caelo 1.12 against those who hold that the world has a beginning but no end. In this far-reaching argument, he aims to show that if something is genēton (generated), it must be phtharton (destructible) and vice versa. Broadie shows that one part of the lengthy argument is intended to show that that which always is cannot ever not-be, and that which always is-not cannot ever be. If this were so, then something that was generated, and hence, was not, will at sometime not be. So, if the universe came to be, then it must come to an end at some time in the future. This argument, however, is followed by another argument to which the first is somehow supposed to contribute. The contribution of the first argument to the second is obscure, since in assuming the truth of the first as a premise, the second is rendered otiose. This leads to the suspicion that the two arguments were not originally developed as part of a single continuous whole. The principal evidence for this, as Broadie carefully and clearly shows, is that in the first argument the terms agenēton and aphtharton are used modally (as in, “necessarily is not generated and necessarily is not destroyed”) whereas in the second argument, “’ agenēton ’ applies to that which is now and of which it was not previously true to say ‘it is-not’, while ‘ aphtharton ’ applies to that which is now and of which it will not later be true to say ‘it is-not’.”
Bolton explores the particular problem of the scientific methodology employed in De caelo. This problem is that the empirical adequacy of scientific conclusions is hard to come by with astronomical phenomena. More precisely, there is a possible variety of mutually exclusive hypotheses relating to such questions as the causes of the motion of the heavenly bodies. Each single hypothesis taken on its own seems to be undetermined. This is certainly true for the mathematical or mathematized accounts of these phenomena. Bolton shows that Aristotle in De caelo repeatedly appeals to the “reasonable” εὔλογον as a criterion for the adequacy of astronomical explanations. This is especially so when he has recourse to Platonic or Pythagorean arguments. As Bolton shows, the criterion of reasonableness is not an alternative to induction, but rather a combination of reflection on perceptual data with the general principles of the study of nature established elsewhere. This approach is otherwise understood by Aristotle to be dialectic. In De caelo, dialectical argument proceeds by using as “commonly accepted premises” the general principles of physics, those that the “wise” or “learned” accept. And here we must suppose that these include those who accept that, for example, Aristotelian principles of motion are ineliminable in any adequate account of the phenomena of nature. Thus, the account in De caelo is at least “on the same level” as the “likely story” of Plato’s Timaeus.
Hankinson gives a highly nuanced and perspicuous account of Aristotle’s argument for the necessity of a fifth element. This argument aims to show that the evidently everlasting and unchanging basic nature of the heavens could not be accounted for if heavenly bodies and the sphere in which they are contained were composed of any of the four terrestrial elements. This is so because each of the latter has a contrary element (or property) from which it is generated and which in turn promotes or necessitates its destruction. As Hankinson shows, differing from what is sometimes claimed, Aristotle is committed to arguing that, since there are two basic types of locomotion—linear and circular—and since the terrestrial elements are associated with the former, i.e., up and down, there must be an element associated with the latter. Since the heavenly bodies, upon analysis, can be shown to move in a circular fashion, there is an easy path to the conclusion that they must be composed of a fifth element, the so-called aither.
Matthen considers the explanatory role of natural place. How, Matthen asks, can, say, the place at which Earth rests, namely, the center of the universe, have a power? It seems implausible that it should have any power since any place is just the innermost boundary of what contains any body, in this case, the mass of the Earth element. Matthen argues that the role or power of natural place is manifested in the stability and impassivity of the Earth when it rests at the center of the universe. Eschewing the traditional view of the final causality of place, Matthen wants to maintain what he calls a “ sui generis principle” with specific application to Earth, namely, “the Aristotelian Schema” according to which “when it is at the center (but not otherwise) the Earth constitutes a stable and impassive unity.”
Gill, too, treats the nature of elemental motion and of natural place. She argues against others, including Matthen, that for Aristotle the elements have only a principle of motion, not a principle of rest. When the elements are at rest in their natural places, this is an impediment to their motion, not the manifestation of a principle they have within. This makes the elements unlike living things, which, because they exist according to nature in the primary sense, have a principle of both motion and rest in them. For Gill, the natural place of an element functions as its form, its active principle, and its principle of rest. Thus, the actuality of an element is to be in its natural place. Since actuality is also a goal, we can equally say that its natural place, or being at its natural place, is the final cause of an element.
Pellegrin’s essay is a treatment of the roles of physical and astronomical theory in De caelo. According to Pellegrin, physical theory focuses on the causes of the heavenly phenomena, particularly the motion of the heavenly bodies, whereas astronomical theory focuses on the correlation of velocity and distance of planetary motion, thus making it primarily a mathematical science. Pellegrin argues for the primacy of physical theory over astronomical theory in De caelo, with the specific result that, for Aristotle, the more physical (and therefore less mathematical) an argument is, the stronger it will be. Pellegrin’s primary example of the application of physical theory is the argument for the sphericity of the universe. He shows how Aristotle argues from the thesis of the circular motion of the outermost heavens to the sphericity of the universe itself via another thesis, that of the interlocking network of spherical homocentric strata within the universe.
Lennox considers the seemingly odd question raised in De caelo : is it legitimate to apply the principles “left” and “right” to the “body of the heavens” and, if so, in what manner? Lennox draws on Aristotle’s De incessu animalium for his effort to see how Aristotle applies principles of animal motion to the heavenly bodies. His goal is expand our understanding of the logical and explanatory structure of Aristotle’s science of nature. We find in De incessu that the directions above-below, front-back, and right-left are present in complete bodies or three-dimensional magnitudes. Above is a principle of length, right is a principle of width, and front is a principle of depth. All three are more “honorable” than their opposites; that is why they are principles. Lennox shows how the directions can and cannot, according to Aristotle, be applied to the heavens. The question about left and right follows from Aristotle’s claim that these can be applied only to the locomotion of self-movers. So, if left and right are applicable to the heavenly bodies, as Aristotle claims, or even to the universe itself, then the heavens and the universe must be among the class of self-movers.
Leunissen examines the role of teleology is Aristotle’s cosmological theory broadly speaking. She notes that teleology is pervasive in the explanations offered in De caelo despite the fact that, in contrast with biology, the need for such explanations is far from obvious. Nevertheless, as Leunissen argues, the biological model is very much in Aristotle’s mind as he attempts to explain specific astronomical phenomena. She further contends that Aristotle is motivated by his desire to make cosmology a “proper natural science” which, therefore, would necessarily have recourse to teleological explanations. These explanations appear in those places where Aristotle attempts to account for certain features and motions of the heavens. They also appear in those places where he wants to explain the absence of certain features. The first sort is fairly obvious; the second is especially interesting since the reason given for the absence of certain features in the heavenly bodies is that if they were present, they would be useless. Stars have no feet because if they did, it would be in vain, and nature does nothing in vain.
Freudenthal’s learned and far-reaching study considers the path in intellectual history from Aristotle’s cosmology to the ancient and medieval rationales for astrology. He takes his story up to Averroes through the crucial stage of Peripatetic thinking in Alexander of Aphrodisias. The basic steps in the path as these. First, Aristotle argued for the claim that the heavens were composed of a fifth element. This radical division between the composition of the superlunary and sublunary bodies, when combined with the general claim in natural philosophy that interaction among bodies requires a commonality of elemental composition, was in some tension with the empirical observation that, nevertheless, the Sun did have a significant effect upon terrestrial life. Rather than abandon the obvious, later Peripatetics were more inclined to generalize the claim about heavenly causality and suppose that all the heavenly bodies must have some effect on things here below even if this effect was occult. In addition, especially in the thought of Alexander, the putative effective powers of the heavenly bodies were a convenient feature of an account of divine providence. This is where, as Freudenthal notes, quoting Maimonides, “astrology comes in.”
This collection, though hardly the place to start in the study of Aristotle’s cosmology, is a useful addition to the literature. The book is well edited and the articles focus on relatively few topics, resulting in some interesting overlapping of discussions and interpretative disagreements.