What however the first lation is must now be shown: and, at the same time, that which is now and was before supposed, that there may be a certain continued and perpetual motion, will be evident by the same method. That no one, therefore, of the other motions can be contintued, is from these things manifest. For all motions and mutations are from opposites into opposites. Thus, for instance, the boundaries to generation and corruption, are being and non-being; but the boundaries to change in quality are the contrary passive qualities; and to increase and diminution, either magnitude or parvitude, and the perfection and imperfection of magnitude, are the boundaries. But contrary motions are those which are into contraries. And that which is not always moved with this motion, but had a prior existence, must necessarily prior to this have been at rest. It is evident, therefore, that the thing which is changed, will be at rest in the contrary. The like also takes place in mutations; for corruption and generation simply assumed, are opposed to that which is simply assumed, and each particular to each. Hence, if it is impossible to be at the same time changed according to contrary mutations, mutation will not be continued, but there will be time between them; for it is of no consequence whether the mutations according to contradiction, are contrary, or not contrary; if only, it is impossible that they can at the same time be present to the same thing: for this is not at all useful to the argument. Nor if it is not necessary to be at rest in contradiction, neither is mutation contrary to rest: (for non-being perhaps is not at rest; but corruption is a motion to non-being) but only if time subsists between; for thus the mutation is not continued. For neither is contrariety useful in things which are prior, but the not being able to exist together at the same time. But it is not proper to be disturbed, because the same thing will be contrary to many, as, for instance, motion to permanency, and to the motion which is to a contrary; for this alone ought to be assumed, that a contrary motion is, in a certain respect, opposed both to motion and rest, just as the equal and the moderate are opposed to that which surpasses, and to that which is surpassed; and that neither opposite motions, nor mutations, can subsist together at the same time. Again, in geaeration and corruption, it may seem to be perfectly absurd, if it is necessary that what is generated should immediately be corrupted; and remain, for no time. Hence, from these things credibility may be obtained in other mutations; for it is natural that the thing should similarly take place in all of them.
