Kitap 9
18
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 writerse.g. Empedocles; cf. Aristot. Met. 5.23.3 n. 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.
19
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.Cf. Aristot. De Gen. et Corr. 337a 1-7. Other potentialities, according to the distinctions already made,Aristot. Met. 9.5.2. 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.
20
The same irrational potentialities can only produce opposite results by their presence or absence.
