Anaxagoras makes the Good a principle as causing motion; for Mind moves things, but moves them for some end, and therefore there must be some other Good—unless it is as we say; for on our view the art of medicine is in a sense health. It is absurd also not to provide a contrary for the Good, i.e. for Mind. But all those who recognize the contraries fail to make use of the contraries, unless we systematize their theories.And none of them explains why some things are perishable and others imperishable; for they make all existing things come from the same first principles. Again, some make existing things come from not-being, while others, to avoid this necessity, make all things one. Again, no one explains why there must always be generation, and what the cause of generation is.
Moreover, those who posit two principles must admit another superior principle, and so must the exponents of the Forms; for what made or makes particulars participate in the Forms? And on all other views it follows necessarily that there must be something which is contrary to Wisdom or supreme knowledge, but on ours it does not. For there is no contrary to that which is primary,since all contraries involve matter, and that which has matter exists potentially; and the ignorance which is contrary to Wisdom would tend towards the contrary of the object of Wisdom; but that which is primary has no contrary.
Further, if there is to be nothing else besides sensible things, there will be no first principle, no order, no generation, and no celestial motions, but every principle will be based upon another, as in the accounts of all the cosmologists and physicists.And if the Forms or numbers are to exist, they will be causes of nothing; or if not of nothing, at least not of motion.
Further, how can extension, i.e. a continuum, be produced from that which is unextended? Number cannot, either as a moving or as a formal cause, produce a continuum. Moreover, no contrary can be essentially productive and kinetic, for then it would be possible for it not to exist;and further, the act of production would in any case be posterior to the potentiality. Therefore the world of reality is not eternal. But there are real objects which are eternal. Therefore one of these premisses must be rejected. We have described how this may be done.
Further, in virtue of what the numbers, or soul and body, or in general the form and the object, are one, no one attempts to explain; nor is it possible to do so except on our theory, that it is the moving cause that makes them one. As for those who maintain that mathematical number is the primary reality,