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[1050b]
[1]
(and hence also
happiness, since happiness is a particular kind of life). Evidently,
therefore, substance or form is actuality. Thus it is obvious by this
argument that actuality is prior in substantiality to potentiality;
and that in point of time, as we have said, one actuality presupposes
another right back to that of the prime mover in each case.It is also prior in a deeper sense; because that which is eternal is
prior in substantiality to that which is perishable, and nothing
eternal is potential. The argument is as follows. Every potentiality
is at the same time a potentiality for the opposite.1 For whereas that
which is incapable of happening cannot happen to anything, everything
which is capable may fail to be actualized.Therefore that which is capable of being may
both be and not be. Therefore the same thing is capable both of being
and of not being. But that which is capable of not being may possibly
not be; and that which may possibly not be is perishable; either
absolutely, or in the particular sense in which it is said that it may
possibly not be; that is, in respect either of place or of quantity or
of quality. "Absolutely" means in respect of substance.Hence nothing which is
absolutely imperishable is absolutely potential (although there is no
reason why it should not be potential in some particular respect; e.g.
of quality or place); therefore all imperishable things are actual.
Nor can anything which is of necessity be potential; and yet these
things are primary, for if they did not exist, nothing would
exist.
[20]
Nor can motion
be potential, if there is any eternal motion. Nor, if there is
anything eternally in motion, is it potentially in motion (except in
respect of some starting-point or destination), and there is no reason
why the matter of such a thing should not exist.Hence the sun and stars and the whole
visible heaven are always active, and there is no fear that they will
ever stop—a fear which the writers2 on physics entertain. Nor do the
heavenly bodies tire in their activity; for motion does not imply for
them, as it does for perishable things, the potentiality for the
opposite, which makes the continuity of the motion distressing; this
results when the substance is matter and potentiality, not
actuality.Imperishable things are resembled in
this respect by things which are always undergoing transformation,
such as earth and fire; for the latter too are always active, since
they have their motion independently and in themselves.3 Other potentialities, according to the
distinctions already made,4 all admit of the
opposite result; for that which is capable of causing motion in a
certain way can also cause it not in that way; that is if it acts
rationally.The same
irrational potentialities can only produce opposite results by their
presence or absence.Thus if there are
any entities or substances such as the dialecticians5
describe the Ideas to be, there must be something which has much more
knowledge than absolute knowledge, and much more mobility than motion;
1 Cf. 19.
2 e.g. Empedocles; cf. Aristot. Met. 5.23.3 n.
3 Cf. Aristot. De Gen. et Corr. 337a 1-7.
5 For this description of the Platonists cf. Aristot. Met. 1.6.7.
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