Kitap 12
10
Now if there is a regular cycle, there must be somethingThe sphere of the fixed stars, Aristot. Met. 12.8.9; cf. Aristot. De Gen. et Corr. 336a 23ff. which remains always active in the same way; but if there is to be generation and destruction, there must be something elseThe sun, which has its own yearly orbit in the ecliptic, and a daily rotation round the earth, which is explained most economically with reference to the rotation of the sphere of the fixed stars. Cf. Aristot. Met. 12.5.3 n., Aristot. De Gen. et Corr. 336a 23ff. which is always active in two different ways. Therefore this must be active in one way independently, and in the other in virtue of something else, i.e. either of some third active principle or of the first.
11
It must, then, be in virtue of the first; for this is in turn the cause both of the third and of the second. Therefore the first is preferable, since it was the cause of perpetual regular motion, and something else was the cause of variety; and obviously both together make up the cause of perpetual variety. Now this is just what actually characterizes motions; therefore why need we seek any further principles?
