Since, however, all mutation is from something into something (but this is evident from the name; for it denotes something after another; and the one signifies prior, but the other posterior) hence that which is changed may be changed in a fourfold respect: for it may be changed either from a subject into a subject; or from a non-subject into a non-subject; or from a non-subject into a subject; or from a subject into a non-subject. But I call the subject that which is rendered manifest by affirmation. Hence it is necessary, from what has been said, that there should be three mutations, that which is from a subject into a subject, that which is from a subject into a non-subject, and that which is from a non-subject into a subject; for that which is from a non-subject into a non-subject, is not mutation, because it is not according to opposition; since they are neither contraries, nor is there contradiction. The mutation, therefore, which is from a non-subject into a subject, according to contradiction, is generation; the simple indeed, that which simply is; but a certain mutation, that which is of a certain thing. Thus the mutation which is from non-white into white is the generation of white; but the mutation from non-being simply into essence, is generation simply, according to which we say, a thing is simply generated, and is not generated some particular thing. But the mutation from a subject into a non-subject is corruption; simply indeed, the mutation from essence into non-being; but a certain mutation, that which is into the opposite negation, as was also said in generations. If, therefore, non-being is predicated multifariously, and neither that which is according to composition or division can be moved, nor that which is according to capacity, which is opposed to being simply considered according to energy; (for that which is not white, or not good, may at the same time be moved according to accident, since that which is not white may be man; but that which is simply not this particular thing, can by no means be moved; since it is impossible for that which is not to be moved;)–if this be the case, it is also impossible for generation to be motion; because that is generated which is not: for though it should be especially generated according to accident, yet, at the same time, of that which is simply in generation, or becoming to be, it is true to say that it is non-being. In a similar manner also with respect to being at rest. But all these absurdities happen from admitting that non-being is moved. And if every thing which is moved is in place; but non-being is not in place; for it would be somewhere; hence, neither is corruption motion: for either motion or rest is contrary to motion; but corruption is contrary to generation. Since, however, all motion is a certain mutation; and there are three mutations, which we have enumerated, but of these, the mutations according to generation and corruption, are not motions; and these are those which subsist according to contradiction; this being the case, it is necessary that the mutation which is from a subject into a subject, should alone be motion. But the subjects are either contraries, or have an intermediate subsistence: for privation is supposed to be a contrary; and it is manifested by affirmation, as the naked, the white, and the black.
