LECTURE 10 (257 a 35-258 a 5)

HOW A THING MOVES ITSELF

1050. The Philosopher has shown that there is no infinite series of movers and mobile objects. Rather there is a first which is either immobile or which moves itself. He shows here that even if there is a first mover which moves itself, it is still necessary to admit a first mover which is immobile.

             This discussion is divided into three parts. First he shows that that which moves itself is divided into two parts, one of which moves and the other of which is moved. Secondly, where he says, 'And since that which . . .' (258 a 6), he shows how such parts are related to each other. Thirdly, where he says, 'From what has been said . . .' (258 b 4), he concludes that there must be a first immobile mover.

             Concerning the first part he makes two points. First he shows that in that which moves itself one part moves and the other is moved, because a whole cannot move itself. Secondly, where he says, 'But it is not . . .' (257 b 13), he rejects other ways in which one might think that a thing moves itself.

             Concerning the first part he makes three points. First he states that a whole self-mover does not move its whole self. Secondly, where he says, '. . . for then, while being . . .' (257 b 3), he proves his position. Thirdly, where he says, 'Therefore, when a thing . . .' (257 b 12), he concludes to his main point.

             1051. Since whole and part are found only in divisible things, he concludes from what was proven in Book VI that whatever is moved must be divisible into things which are always divisible. For this is the nature [ratio] of a continuum, and whatever is moved is a continuum, if it is moved per se. (It is not impossible for an indivisible thing to be moved per accidens, for example, a point or whiteness.)

             This was explained above in Book VI. Everything which he said before Book VIII he called 'universal in nature'. But in Book VIII he begins to apply to things what he has said above about motion in general. Therefore, since that which is moved is divisible, a whole and a part can be found in everything which is moved. Hence if there is something which moves itself, whole and part will be found in it. But the whole cannot move the whole itself (that is, it cannot totally move itself).

             1052. Next where he says, '. . . for then, while being . . .' (257 b 3), he proves his position with two arguments, the first of which is as follows.

             The motion of a thing which moves itself all together and at once is one in number. If, therefore, a thing moves itself such that the whole moves the whole, then it follows that the mover and the thing moved are one and the same in respect to one and the same motion, whether it be local motion or alteration.

             But this seems to be inconsistent, because a mover and a thing moved are opposed to each other. But opposites cannot be in the same thing in the same way. Hence it is not possible that the mover and the moved be the same in respect to the same motion. For when a thing both moves and is moved, the motion by which it moves is different from the motion by which it is moved. For example, when a stick which is moved by a hand moves a stone, the motion of the stick and the motion of the stone differ in number. Thus, it would follow further that one will teach and be taught at the same time with respect to one and the same knowable object. Similarly, one will heal and be healed with respect to numerically one and the same health.

             1053. Next where he says, 'Moreover, we have established . . .' (257 b 6), he gives the second argument, which is as follows.

             It was established in Book III that what is moved is mobile, that is, it exists in potency. For that which is moved is moved insofar as it is in potency and not in act. For a thing is moved because, when it is in potency, it tends toward act. But that which is moved is not in potency in such a way that it is in no way in act, because the motion itself is a certain act of the mobile object insofar as it is moved. But this act is imperfect, because it is its act insofar as it is still in potency.

             But that which moves is already in act, for what is in potency is reduced to act only by that which is in act. A mover, for example, heats when it is hot, and that which has a generated species generates, as a man generates that which has a human species, and the same is true of other things. Therefore, if a whole moves itself as a whole, it follows that the same thing in the same respect is both hot and not hot, for insofar as it is a mover it is actually hot, and insofar as it is moved it is potentially hot.

             And the same applies to all other cases in which the mover is 'univocal', that is, the same in name and in nature [ratio] as that which is moved. For example, just as heat causes heat, so man generates man.

             He says this because there are some agents which are not univocal in name and in nature [ratio] with their effects. For example, the sun generates a man. Even though the species caused by such agents is not the same in nature [ratio], nevertheless in a certain higher and more universal way it is the same. And so, it is universally true that the mover is in act in a certain way with respect to that to which the mobile object is in potency. Therefore, if a whole moves itself as a whole, it follows that the same thing is simultaneously in act and in potency, which is impossible.

             From this he concludes to his main point; namely, in that which moves itself, one part moves and another is moved.

             1054. Next where he says, 'But it is not . . .' (257 b 13), he rejects certain ways in which someone might think that a thing moves itself.

             First he shows that in a thing which moves itself each part is not moved by another. Secondly, where he says, 'But as a matter . . .' (257 b 27), he shows that in a thing which moves itself no part moves itself.

             Concerning the first part he makes two points. First he states his intention. Secondly, where he says, 'In the first place . . .' (257 b 15), he proves his position.

             He says, therefore, first that it is clear from what follows that a thing does not move itself in such a way that each part of it is moved by the remaining part. For example, if A B moves itself, then A moves B, and B moves A.

             1055. Next where he says, 'In the first place . . .' (257 b 15), he proves his position by four arguments. It should be noted that to reach this conclusion he repeats the arguments given above to show that not every mover is moved by another. Hence from the foregoing he here briefly summarizes four arguments.

             The first of these he takes from the first argument above which he gave in a double order to show that a thing is not moved by another to infinity. For otherwise there would not be a first mover. And when the first mover is removed, so are the subsequent movers. Hence here he also sets forth the same inconsistency.

             He says that if in the first thing moved (which is given as a mover of itself) each part is reciprocally moved by another, then there is no first mover. This is so because, as was said above, a prior mover is the cause of motion more than a later mover.

             He also proved above that a thing moves in two ways. In one way a thing moves because it is moved by another, for example, a stick moves a stone because it is moved by a hand. This is a second mover. In another way a thing moves because it is moved by itself, as a man moves. And this is the disposition of a first mover. Moreover, that which moves, but not because it is moved by another, is further removed from the last thing which is moved, and is closer to the first mover, than an intermediary which moves because it is moved by another.

             This argument ought to be developed as follows. If in a whole which moves itself each part moves the other reciprocally, then one part does not move more than another. But a first mover moves more than a second mover. Therefore, neither of them will be a first mover. But this is inconsistent, because then it would follow that that which is moved by itself is not closer to the first principle of motion (which follows no being) than that which is moved by another. But it was shown above that that which moves itself is first in the genus of mobile objects. Therefore, it is not true that in things which move themselves each part is moved by another.

             1056. Next where he says, 'In the second place . . .' (257 b 20), he develops two arguments for the same thing from the first argument which he gave above to show that not every mover is moved such that 'being moved' is in the mover per accidens. In the above argument he developed two conclusions; first, a mover need not be moved; and second, motion is not eternal. From these two conclusions he formulates two arguments.

             First he says that it is not necessary for a mover to be moved by itself except per accidens. And he observes that unless the first mover is understood to be moved by itself, it will not be necessary for the first mover to be moved per accidens. For some have held that every mover is moved, but this occurs per accidens.

             When, therefore, it is held that in a self-mover the part which moves is moved by a contrary and equal motion from another part, this will occur only per accidens. But, as we agreed above, that which is per accidens can not-be. Therefore it happens that that part which moves is not moved. Hence it follows that one part of the self-mover is moved, and the other part moves and is not moved.

             1057. Next where he says, 'In the third place . . .' (257 b 23), he gives another argument which corresponds to the second conclusion drawn above, that is, the conclusion that motion is not eternal. Here, however, he argues in the reverse order.

             If motion must be eternal, it is not necessary that a mover be moved in return when it moves. What is necessary is that a mover be either' immobile or that it be moved by itself.

             The reason for this condition is clear from the argument advanced above. For if a mover does not move unless it is moved, and if there is no 'being moved' in it except per accidens, then it follows that it happens to be not moved. Consequently, it does not move, and hence there will be no motion. But it was shown above that motion is eternal. Therefore, it is not necessary for a mover, when it moves, to be moved in return. And so it is not true that each part of a self-mover is moved by another.

             1058. Next where he says, 'In the fourth place . . .' (257 b 25), he gives the fourth argument which he takes from the argument given above to show that 'being moved' is not present per se in a mover which is moved. For otherwise it would follow that the mover is moved by the same motion by which it moves, as was explained above.

             Thus, by abridging this argument here, he says that if each part is moved by another, it follows that it moves and is moved in respect to the same motion. Hence it follows that that which heats becomes hot, which is impossible.

             Therefore, if each part of a self-mover is moved by another, it follows that a thing moves and is moved in respect to the same motion. For in a self-mover there is one motion, and the part which moves must be moved in respect to that motion.

             1059. Next where he says, 'But as a matter . . .' (257 b 27), he rejects another way of explaining this; namely, in a self-mover a part moves itself.

             First he states his position. Secondly, where he says, 'For, if the whole . . .' (257 b 29), he proves his position.

             He says, therefore, first that if there is a first self-mover, it cannot be said either that one part of it moves itself, or that each one of many parts moves itself.

             1060. Next where he says, 'For, if the whole . . .' (257 b 29), he proves his position with two arguments, the first of which is as follows.

             A whole is moved by itself either because one of its parts is moved by itself or because the whole is moved by itself.

             If it is moved because of its part, then that part will be the first self-mover, because that part when separated from the whole will move itself. And the whole will not be the first self-mover, as was granted.

             If, then, it is said that the whole moves itself by reason of the whole, then it is only per accidens that some parts move themselves. But what is per accidens is not necessary. Therefore, in the first thing which moves itself, it must be admitted that the parts are not moved by themselves. Therefore, of the whole first self-mover one immobile part will move, and the other will be moved. For it is possible for a moving part to be moved only if it is moved by another part which moves, or if it moves itself.

             It must be noted that Aristotle, by rejecting these two ways, intends to conclude that a moving part in a self-mover is immobile; not, however, that a self-mover is divided into two parts, of which one moves and the other is moved. For it was sufficiently explained in the beginning that a whole does not move itself as a whole.

             And so it is clear that it was not necessary for Aristotle to make a five-fold division, as some have said. One alternative is that the whole moves the whole; the second is that the whole moves a part; the third is that a part moves the whole; the fourth is that two parts alternately move themselves; the fifth is that one part moves and the other is moved. For if the whole does not move the whole, for the same reason it follows that the whole does not move a part, nor a part the whole, because in either case it will follow that a moved part moves itself. Hence the fact that the whole does not move the whole is sufficient to conclude that one part moves and the other is moved. But to conclude that the part which moves is not moved, he proves two other things; namely, the moving part is not moved by something which is moved, and it is not moved by itself.

             1061. To prove this second point he introduces a second argument where he says, 'Further, if the whole moves itself . . .' (258 a 3). The argument is as follows.

             If it is granted that the moving part of a self-mover moves itself as a whole, then from the above proof it will follow further that one part of it moves and the other is moved. For it was shown above that a whole does not move itself in any other way except that one part of it moves and the other is moved. Let the moving part of a self-mover be AB. From the foregoing argument it follows that one part of it will be the mover, namely A, and the other part will be moved, namely B. If, then, the whole AB moves itself, as was granted, it follows that the same thing is moved by two movers, that is, by the whole, which is AB, and by the part, which is A. But this is impossible. Therefore, it follows that the moving part of a self-mover is absolutely immobile.