Book 13
17
We have now examined and analyzed the questions concerning numbers to a sufficient extent; for although one who is already convinced might be still more convinced by a fuller treatment, he who is not convinced would be brought no nearer to conviction.
18
As for the first principles and causes and elements, the views expressed by those who discuss only sensible substance either have been described in the PhysicsAristot. Physics 1.4-6. or have no place in our present inquiry; but the views of those who assert that there are other substances besides sensible ones call for investigation next after those which we have just discussed.
19
Since, then, some thinkers hold that the Ideas and numbers are such substances, and that their elements are the elements and principles of reality, we must inquire what it is that they hold, and in what sense they hold it.
20
ThoseThe Pythagoreans and Speusippus. who posit only numbers, and mathematical numbers at that, may be considered laterAristot. Met. 14.2.21, Aristot. Met. 14.3.2-8, 15, 16.; but as for those who speak of the Ideas, we can observe at the same time their way of thinking and the difficulties which befall them. For they not only treat the Ideas as universal substances, but also as separable and particular.
