But that in which a thing is first changed, is predicated in a two-fold respect: one, that in which primarily the mutation is perfect; for then it is true to assert, that it has been changed; but the other, that in which it began to change. Hence, that which is said to be first according to the end of the mutation, is inherent, and is; for it is possible that mutation may be perfected, and there is an end of mutation, which has been shown to be indivisible, because it is a boundary. But in short, there is not mutation which is predicated with reference to the beginning; for there is not a beginning of mutation, nor a time in which a thing is changed. For let A D be a first time. This, therefore, is not indivisible; for it would happen that nows would adhere to each other. Again, if it is at rest in the whole time A C, (for let it be supposed to be at rest) it will also be at rest in A. So that if A D is without parts, it will at the same time be at rest, and have been changed; for it is at rest; in A, but is changed in D. Since, however, A D is not without parts, it must necessarily be divisible, and have been changed in every part of it: for A D being divided, if it has been changed in neither part, neither will it have been changed in the whole; but if it changes in both, it will also change in the whole; and if it is changcd in one of these, it is not first changed in the whole. So that it is necessary it should have been changed in every part. It is evident, tlrerefore, that the time in which a thing is first changed; because the divisions are infinite. Hence, neither of that which is changed, is tbere any first part which is changed: for let D F be that which is first changed of D E; since it has been shown that whatever is changed is divisible. But let the time in which D F is changed be H I. If therefore D F is changed in the whole time, that which is changed in half the time will be less, and prior to D F. And again, there will be another part prior to this, and another prior to that, and thus perpetually. So that there will be nothing first changed, of that which changes. That there is not, therefore, any thing first, neither of that which changes, nor of the time in which it is changed, is evident from what has been said. But that which changes, or that according to which it changes, will no longer subsist in a similar manner: for there are three things which are considered in mutation; that which changes, that in which, and that according to which it changes; as, for instance, man, and the time, and that which is white. Man, therefore, and the time, are divisible. But concerning that which is white there is another reason; except that all divisible things are according to accident: for that to which quality or whiteness happens, is divisible: for with respect to such things as are said to be divisible essentially, and not according to accident, neither in these will there be that which is first; as, for instance, in magnitudes: for let there be a magnitude A B, and let it be first moved from B to C. If, therefore, B C is indivisible, that which is without parts will adhere to that which is without parts. But if it is divisible, there will be something prior to C, into which it will have been changed, and again something prior to that, and thus perpetually, because division never fails. So that there will not be a first into which it will be changed. The like also will take place in the mutation of quantity; for this too is in continuity. It is evident, therefore, that in that motion alone which is according to quality it is possible for the essentially indivisible to subsist.
