If, however, there is any thing of such a nature, as always to move being immoveable, and it is itself perpetual, it is also necessary, that the nature which is first moved by this should be perpetual. But this is manifest, indeed, because there would not be generation and corruption, and mutation in other things, unless something moved being moved; for that which is immoveable, will always move with the same and with one motion, after the same manner, because it is not always changed with reference to that which is moved; but that which is moved by the immoveable, or by that which is now moved, because it is differently affected with respect to things, will not be the cause of the same motion, but, through being in contrary places or forms, will cause each of other things to be moved with contrary motions, and at one time to be at rest, and at another to be moved. From what has been said also, that becomes evident of which we doubted in the beginning, viz. why all things were not either moved or at rest; or some things were always moved and others always at rest; and some things were sometimes moved, and sometimes not. For the cause of this is now manifest; because some things indeed are moved by that which is perpetually immoveable, and therefore are always changed; but others are moved by that which is moved and changed, and therefore are themselves necessarily changed. But another thing, as we have observed, is immoveable; as being that which remaining simply, and after the same manner, and in the same, produces one simple motion.
