This, however, takes place in a twofold respect: for either it is not through that which itself moves, but through something else which moves the mover; or it is through itself. And this is either the first after the last, or it moves through many media. Thus, a staff moves a stone, and is moved by a hand, which is moved by a man; but man no longer moves because he is moved by something else. We say, therefore, that both move, as well that which is the last, as that which is the first of the movers. But that is more a mover which is the first; for it moves that which is the last mover, but this does not move the first. And without the first mover indeed, the last will not move, but the first will move without the last. Thus a staff will not move unless a man moves it. If, therefore, it is necessary that every thing which is moved should be itself moved by something, it is also necessary that it should either be moved by that which is moved by another, or that it should not be moved by it. And if it is moved by that which is moved by another, it is necessary that there should be some first mover, which is not moved by any thing else. But if the first mover is a thing of this kind, it is not necessary that the other likewise should be so: for it is impossible that a thing which moves, and which is itself moved by another should proceed to infinity; since of infinites there is no first. If, therefore, every thing which is moved is moved by something, but that which first moves is indeed moved, yet not by another, it is necessary that it should itself be moved by itself. Again, it is possible also to discuss this affair as follows: Every thing which moves, moves something, and through something; for that which moves, either moves through itself or through another. Thus a man moves, either through himself, or through a staff·; and the wind throws something down, either by itself, or through a stone which it impels. But it is impossible for that which moves to move, without that which moves from itself. If, however, a things moves itself from itself, it is not necessary that there should be something else through which it moves. But if that through which it moves is something ditfetent, there is something which moves not from any thing else, but from itself; or there will be a procession to infinity. If, therefore, something moves being moved, it is necessary to stop, and not proceed to infinity; for if a staff moves in consequence of being moved by a hand, the hand moves the staff. But if through this it moves something else, there is also something else which moves this. Since, however, it always moves something else through something, it is necessary that should be prior, which itself moves itself. If, therefore, this is indeed moved, but there is not any thing else which moves it, it is necessary that it should move itself. Hence, according to this reasoning, either that which is moved, is immediately moved by that which moves itself, or some time or other it will arrive at a thing of this kind. In addition to what has been said, to those who consider, the following particulars also will be found to happen: for if every thing which is moved, is moved by that which is moved, either this will be inherent in things accidentally, so as for that which is moved to move, yet, not because it is itself moved; or it will not be inherent in things from accident, but essentially. In the first place, therefore, if it is inherent accidentally, it is not necessary for that which is moved also to be moved. And if this is admitted, it is evident that it may be possible, some time or other, that nothing may be moved; for accident is not necessary, but may not exist. If, therefore, we admit that to be which is possible, nothing impossible will happen, but perhaps that which is false. But for motion not to exist is impossible; for it was before demonstrated, that it is necessary motion should always exist. And this happens conformably to reason: for it is necessary that there should be three things, viz. that which is moved, that which moves, and that by which it moves. With respect to that which is moved, therefore, it is necessary indeed that it should be moved, but it is not necessary that it should move. But with respect to that by which it moves, it is necessary that it should both move and be moved: for this is co-changed, since it subsists at the same time, and according to the same with that which is moved; as is evident in things which are locally moved: for it is necessary that they should thus touch each other, as far as to a certain thing. But that which moves so as not to be that by which it moves, is immoveable. Since, however, we see that which is last, which indeed may be moved, but does not possess the principle of motion; and since we also see that which is moved indeed, but by another, and not by itself, it is reasonable, not to say necessary, that there should be a third thing which moves, being immoveable. Hence Anaxagoras also speaks rightly, when he says, that intellect is impassive and unmingled; because he makes intellect to be the principle of motion; for thus alone can it move, being: immoveable, and have dominion, being unmingled.
If, however, that which moves is not moved according to accident, but from necessity; and if unless it is moved, it will not move, it is necessary that that which moves, so far as it is moved, should either be so moved, as to be moved according to the same or a different species of motion. I say, for instance, either that which heats must also be itself heated, and that which imparts health must also be made healthy, and that which carries must be itself carried; or that which imparts health must be carried, and that which carries must be increased. It is evident, however, that this is impossible: for it is necessary to speak dividing as far as to individuals; just as if something should teach how to geometrize, this same thing should also be taught to geometrize; or if any thing throws, that it should also be thrown, according to the same mode of throwing; or not in this manner indeed, but a different thing from a different genus; as, for instance, for that which carries, to be increased, but that which increases this, to be changed in quality by something else; and for that which causes this to be changed in quality, to be moved according to some other motion. But it is necessary to stop; for motions are finite. To say, however, that a reversion again takes place, and that a thing which produces change in quality is carried, is to do the same thing, as if any one should immediately say, that which carries is carried, and that which teaches is taught: for is is evident, that every thing which is moved, is also moved by a superior mover, and that it is more moved by that which is prior among movers. This, however, is impossible; for it will happen that the teacher will learn; of which two it is necessary that the one should possess, and that the other should not possess science. Farther still, it will happen, which is still more absurd, that whatever is motive will be moveable, if every thing which is moved, is moved by that which is moved: for it will be moveable. And this is just as if someone should say, that every thing which has the power of imparting health, is also capable of being made healthy; and that every thing which has the power of building may be built, either immediately, or through many media. I say, for instance, it is just as if every thing which is motive, is moveable by something else, yet it is not moveable with the same motion by which it moves a thing near, but with a different motion; just as if that which has the power of imparting health could learn. This ascent, however, will sometime or other be terminated in the same form, as we have before observed. One, therefore, of these is impossible; and the other fictitious: for it is absurd that a thing which is capable of producing a change in quality, should necessarily be capable of being increased. It is not therefore necessary, that a thing which is moved should always be moved by another, which also is itself moved. The procession, therefore, will stop. Hence that which is first moved, will either be moved by that which is at rest, or it will itself move itself. However, though it should be necessary to consider, whether that which itself moves itself is the cause and principle of motion, or that which is moved by another, every one should admit the former: for that which is a cause through itself, is always prior to that which is a cause through another.
