XENARCHUS, ALEXANDER, AND SIMPLICIUS ON SIMPLE MOTIONS, BODIES AND MAGNITUDES

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    Some of the ideas of this paper were presented to a conference on de Caelo and the commentators organized by the CNRS in Paris in June, 2000. Others were first floated at a faculty seminar at Austin in April 2001; I would like to thank my audience there, in particular Alex Mourelatos, Steve White, and Richard Sorabji, for their helpful and friendly comments: Richard also read and remarked upon a written version. Finally, Tim O'Keefe read the penultimate draft and made a number of valuable suggestions, of both style and substance.

Abstract

Abstract  Aristotle accounted for the fundamental dynamics of the cosmos in terms of the tendencies of the various elements to distinct types of natural motions, and (in the case of the sublunary elements) to rest in their natural places. In so doing, he introduced a fifth element, the ether, with a natural and unceasing tendency to revolve, as the matter for the heavenly bodies. This paper deals with some of the objections raised to this model, and to its conceptual underpinnings, raised by Xenarchus of Seleuceia, an unorthodox Peripatetic of the 1st century BC, and of the attempts of later philosophers to rebut them. In so doing it casts light on a little-known, but historically important and interesting, episode in the development of physical dynamics.

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