Diodorus Kronus on Motion against Aristotle’s Kinematics

Marion, Florian
(2017) First Dublin Graduate Conference in Ancient Philosophy. Physis and Psychê in Ancient Philosophy: Causes, Generation, and Change — Location: University College Dublin/Trinity College Dublin, Dublin (31.March.2017)

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Megaric Philosopher Diodorus Kronus forcefully argued against the very subsistence of motion. The strength of the argument explains why Sextus Empiricus preferred it to Zeno’s in his discussion of change and motion (AM, X, 85-120). Scholars usually consider De Int, 9 and Phys, 6 to be Aristotle’s response to Diodorus’ argument. However, a close reading of Phys, 6.10 shows us that: 1) Aristotle actually predates Diodorus; the way the argument is expressed in Aristotle differs from Diodorus formulation. Aristotle’s text is rather a discussion of Plato’s Parm, 138d-139a (perhaps 156c-e as well). Only in AM, X, 142-143 does Sextus report Diodorian argument expressed in Aristotle’s way. 2) Diodorus’ argument against motion is actually a reply to Aristotelian Kinematics and Dynamics, viz. a defence of the traditional Megaric rejection of δύναμις (Met, Θ, 3). We shall investigate why Aristotle cannot easily reply to the difficulty brought up by Diodorus by analysing the several meanings of ‘δύναμις’ and ‘τόπος’, and by discussing shortly finalism. This makes the absence of response from Neoplatonic commentators to Diodorus’ argument understandable: the argument poses too strong a difficulty for their kinematics, which is heavily inspired by Aristotle. However, Damascius’ writings still display a reminiscence of the argument, which may have inspired him the twist he imposes to Aristotle’s physics (In Parm, II, 241, 29-242, 15; Simpl, In Phys, 796, 32-797, 13). Quite unlike what is the case for the kinematics, their dynamics is not threatened by the argument, even only the Platonic thesis of psychic self-motion likely dissolves the Diodorian obstacle. Ultra-orthodox Plotinus, unlike them, finds support in the argument to reply to Alexander’s Neo-Aristotelianism (In Phys, scholium 435) and the exegetic tendencies of his pupil Porphyry (Enneads, VI, 1 [42], 16). Ironically, in reason of his hylomorphic reading of the Timaeus, Plotinus doesn’t understand the mathematical background of Plato’s Dynamics which assimilate the ideas of motion and algorithm, viz. the mathematical motion is essentially independent of time. Only some Islamic “Platonizing” mathematicians like Thābit ibn Qurra and Ibn al-Haytham have pursued the Platonic intuition. This is clear in the context of the discussion of the Euclidean fifth postulate where they introduce explicitly motion into geometry (unlike ’Umar al-Khayyām and Neoplatonic commentators who hold onto the Aristotelian Doctrine of Phys, II, 2, 193b22-194a7; Met, A, 8, 989b31-33). They also maintained a theoretical distance between geometry and mechanics, as well as asserted the thesis that kinematics is nothing but the examination of the geometrical figures of the completed movements. To them, a portion of geometry is essentially dynamical (even, for al-Haytham, geometry must be entirely revised and systematized by means of the fundamental notion of motion), as another portion of mathematics – algorithmics. This overview of these Platonizers makes it clear how Diodorus’ argument against motion could be used as an amphibious objection to Aristotelian Kinematics and Dynamics, implying a rejection of the Neoplatonic ideal of a deep harmony between Plato and Aristotle and, consequently, a strong support of the Platonic self-motion of the soul.
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Marion, F. (2017). Diodorus Kronus on Motion against Aristotle’s Kinematics. First Dublin Graduate Conference in Ancient Philosophy. Physis and Psychê in Ancient Philosophy: Causes, Generation, and Change, University College Dublin/Trinity College Dublin, Dublin.