Nature, change and agency in Aristotle's Physics
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The concept of "nature as inner principle of change" is fundamental to Aristotle's theory of the physical world; it is the object of the present thesis to substantiate this claim by tracing the effects of this idea in Aristotle's rejection of materialism, in his doctrine of "natural places", in his definition of change and process in general, and (via the latter) in his notion of agency in general and the supreme Unmoved Mover in particular ((1)). Aristotle elucidates "natural" by . contrast with "artificial" ((2) - (3)), holding that natural substances not merely collectively ((4) - (5)) but as individuals each possess an 'innate impulse of change'. But this must be explained so as to allow for the fact that no change is entirely independent of external conditions ((6) - (7)). If, however, change were totally dependent on external conditions, its occurrence would be inexplicable ((8) - (9)), and the very concept of "change" would be incoherent. This latter conclusion emerges from an examination of the ancient paradox of becoming and Aristotle's treatment of it ((10) - (33)). The paradox is expounded ((11) -(14)). Aristotle answers it by showing that language assumes a continuing subject of change ((15) - (21)). But this assumption meets the problem only if the metaphysical category of substance is also assumed, and along with it some distinction between substance-constitutive and non-substance-constitutive characteristics ((22) - (27)). The former mark off their subject as a thing of a certain causal type; thus change, in presupposing a substantial subject (see also Appendix to Chapter 1), presupposes one that makes some causal contribution to its own changes ((28) - (33)). But Aristotle means more than this by 'nature as inner principle'. He holds a natural substance to be (like a craftsman) the autonomous determinant of certain changes; these therefore (by contrast with changes not so determined) are "natural", as manifesting the substantial nature ((34) - (36)). This problematic notion is taken for granted by Aristotle in the Vhys-ics ((37) - (39)), but can be seen to rest on his metaphysic of substance. It is a consequence of this that the natural change of a given substance be of one kind and display a unitary pattern reflecting the unity of the substance ((40)). This view cripples scientific method as we understand it ((41)), but Aristotle's idea of substance anyway cuts him off from the approaches successfully operated in later mechanics and chemistry ((42) - (45)). A summary of the ground so far covered ((46)) introduces a further sense in which Aristotle's natures are "inner" principles of change: the subject of change is not (as in artifice) external to the being which is the source of change ((47) - (54)).