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))