In his recent book Aristotelian explorations, Geoffrey Lloyd devoted a chapter to "Heavenly aberrations: Aristotle the amateur astronomer". 1 The purpose of this paper is to point out two further major supposed aberrations that are rarely recognized but have serious consequences, one in Aristotle and one in Plato. IThe problem in Aristotle stems from the difficulties he faces in giving a coherent account of interaction between the celestial and terrestrial realms.' He has to be able to explain how the heavenly bodies can generate heat and light and transmit them to the terrestrial realm without compromising their status as unchanging, eternal entities. The answer he gives in De caelo 11/7 is that just as missiles in flight become heated and affect the air around them, so the air that lies beneath each celestial body is heated by their motion. Aristotle does not specifically state that this heating causes ignition in De caelo 11/7, but De caelo 289a24 ff. talks of missiles and motion igniting (ekpuroutai) and affecting the air in the same way. He naturally emphasises that the celestial bodies themselves cannot ignite. In Meteorologica 1/3, we are straightforwardly told that the motions of the celestial bodies' set on fire (ekpuroutai) the parts of the lower world nearest to them, and that motion can inflame (ekporoun) air. This I shall call "the ignition theory" of the generation of celestial light.There are some well known physical objections to the coherence of Aristotle's account in De caelo.' Given what he says about the arrangement and natural place of the elements, is it not fire rather than air that is closest to the heavenly bodies?' If there are no terrestrial elements in the celestial realm, how are bodies other than the Moon able to affect the terrestrial realm, especially as there are retroactive spheres specifically designed to prevent the transmission of their motion?' As far as possible I wish to leave the physical issues on one side, however, and concentrate on the implications this theory has for astronomy.' IIAt no point when discussing the ignition theory in De caelo does Aristotle dtaw any distinction between the bodies that generate their own light and those that do not, and he does not mention reflected light at all. De caelo 11/7 speaks quite generally of the stars, meaning all the celestial bodies, using plurals throughout, and at 298a28 refers to "the upper bodies which are carried in spheres" and how their motion heats
The nature of the receptacle, presented at Timaeus 48e-53b, is controversial. It is unclear whether the receptacle is supposed to be matter, or whether it is supposed to be space, or whether it is in some way both matter and space. Plato seems to intend some reform of the way in which we refer to the phenomena, but the nature of that reform is far from clear. 1 Can the evidence of Aristotle help us here ? Aristotle and some of his commentators have some interesting and significant things to say about the receptacle and its contents, more perhaps than is generally recognised. Some commentators believe that the receptacle passage, Timaeus 48e-53b, is self-contained and can be taken in isolation from the rest of the Timaeus. In my view that is quite wrong. Geometrical atomism (GA) is introduced at 53c. By geometrical atomism I mean the theory that the elements (earth, water, air, fire) can be analysed into three-dimensional particles of definite shape (cubes, octahedra, eikosahedra, tetrahedra, which I shall call 'atoms', in the modern sense), and that these particles can be further subdivided into planes, and that these planes can be further subdivided into one of two types of triangle. GA does not sit entirely easily with the receptacle passage. It may develop or modify the receptacle theory, and certainly it has a considerable bearing on the nature of the receptacle. At the very least we need to think carefully about how the entities proposed by GA relate to the receptacle. What is undeniable is that the rest of the Timaeus (53c ad fin) discusses the phenomena in terms of GA and not the receptacle. We get an analysis of objects, human beings, human perception, and of qualities as a result of the interaction of objects and human beings, entirely in terms of GA without any mention of the receptacle. In my view we often underrate the importance of GA in relation to the receptacle. It may well be the case that Plato was primarily interested in philosophy rather than science, and that, to us, the receptacle is interesting 'live' philosophy, while GA is merely redundant 'dead' science. However, Plato in the Timaeus was interested in at least the broad outlines of a teleological account of the cosmos and humans, and GA is certainly an important and integral part of that. What we find philosophically interesting in the Timaeus is no sure guide to what 1 There is a large literature on the receptacle. The most interesting recent contributions, which have references to the earlier literature, are K. A. Algra,
Whether the astronomy of the Timaeus had any significant influence on Eudoxus' theory of homocentric spheres is a matter of contention. Some commentators deny any such influence.' Here I argue for a view of the Timaeus' astronomy, and of Eudoxus' astronomy, whereby Eudoxus' work was as much a natural development of the Timaeus as Callippus' work was of Eudoxus. I also argue for an important interpretative principle. This is that Plato, Eudoxus and Callippus could not account for all the phenomena they were aware of, and were aware of that fact. If the Timaeus presents a prototype, Eudoxus can then be seen to develop this astronomy, making the model more sophisticated and complex while staying within the cosmological principles, and attempting to solve the key problems which were left unsolved by the Timaeus model. He does this in much the same way as Callippus made Eudoxus' model more complex and sophisticated, and attempted to solve the leading problems in that model. I also consider some further objections to a significant interaction between Plato and Eudoxus, based on supposed philosophical differences, dating, and the evidence of later commentators. I conclude that these provide no significant obstacle to considering there to be a fruitful liaison between Plato and Eudoxus. I The model proposed by the Timaeus was a significant advance on any previous model we are aware of, including Plato's model in the Republic's myth of Er.' Most notably J. Mittelstrass. Die Refrung der Phanomene (Berlin 1963). W. R. Knorr, 'Plato and Eudoxus on the planetary motions', J.Hisr.Astron. 21 (1990) 313-29, L. Zhmud, 'Plato as "architect of science", Phronesis 43/3 (1998)211-44. Ancient approaches to Plato 's 'Timaeus' 5 6 ANCIENT APPROACHES TO PLATO'S TIMAEUS Philolaus.' Republic, myth of Er.3n The basic problem with these models can be put like this. The earth effectively has two motions, a daily rotation and its annual orbit of the sun.4 The axes of those motions are not identical.Earth's axes. The earth's axis of rotation is offset from the plane of its orbit around the ~ i -If we treat the earth as being central and stable, and so transfer these motions to the heavens, there need to be two axes of rotation, one for the fixed stars and one for the sun and the other bodies of the solar system. This, in effect, is what we get for the first time in the Timaeus. See Aristotle, Cael. 293a18ff.. cf. Meraph. A 5 986a10-12. See Plato, Republic 616b ff. Ignoring the motion of the earth's axis of rotation, the effect of which (the precession of the equinoxes) had yet to be discovered. Winter Equinoxes Summer Solstice Solstice 23.5 Due West 23.53 ' One can also have good explanations of the phases of the moon and the periods of the planets, but previous models had managed these as well.
This work is a study of theoretical treatments of how the world came to be, from the Presocratics to late antiquity. It takes the theories as quasi-scientific proposals, based at least in part on scientific criteria. 'A key argument of this book', explains Gregory, 'will be that there are perennial philosophical and scientific problems relating to cosmogony' [2]. Recognizing that most interpreters of ancient Greek philosophy view cosmogony 'as a single issue', and see it as ancillary to philosophical questions, the author wishes to show that cosmogony can be a complex subject that motivates debates among thinkers [1].
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