Commentary Aristotle Physics
1168. Then, at “moreover, the mover” (267b6), he shows where the beginning of the first continuous motion is. And, because it was proved that the first motion is circular and belongs to a circular magnitude, the first beginning of this motion must be either in the middle (that is, the center) or on the circle, because both are principles of a circular magnitude. For in a circular magnitude, lines are extended from the center to the circumference. Hence, one of these must be taken as principle, and the other as terminus.
Then he shows by the following argument that the principle of the first motion is on the circle. Every motion, the closer it is to the moving principle, the swifter it is, because it receives a stronger impression from the mover. But we perceive in the motion of the whole firmament, which motion proceeds from the first immobile mover, that the closer some mobile approaches the outermost circumference, so much the swifter is its motion. Therefore, the mover is on the circle and not in the center.
The major premise of this argument is plain. But, in order to make the minor plain, it must be considered that a twofold motion is found in heavenly bodies:
one is the motion of the entire firmament in its daily revolution from east to west, and this is the first motion;
the other is the motion by which the stars are moved contrariwise from west to east.
Now, in this second motion, the closer a heavenly body is to the center, the swifter its motion, as is evident from the calculations of astronomers, who assign one month for the motion of the Moon, one year for the motions of the Sun, Mercury, and Venus, two years to Mars, twelve years to Jupiter, thirty to Saturn, and thirty-six thousand years to the fixed stars.
But, with respect to the motion of the entire firmament, it is the opposite. For the farther a heavenly body is from the earth, the swifter is its motion, because it traverses a larger magnitude in the same time. For the circumferences of circles are greater the farther they are from the center, and yet all the heavenly bodies are revolved with the motion of the whole in the same period of time. Consequently, the outermost bodies are swifter. Hence, what remains is that the principle of the first motion is not in the center but on the circumference.
1169. But now a difficulty arises about this conclusion. For the first mover, as he will conclude below, is indivisible and has no magnitude, and its power does not exist in a magnitude. But whatever is such does not seem to have a definite position in a body. Hence, it does not befit the first mover to be in one part of the first mobile more than in another.
But it should be stated that the first mover is said to be in some part of its mobile not through any determination of its substance, but through its efficient causality of motion, because it begins to move at some part of the object it acts upon. And it is for that reason that the first mover is said to be in the heavens rather than in the earth, and rather in the east, where the motion begins.
And this is not to be understood as though the mover fixes itself to some definite part of the mobile, since there is no definite part of the mobile always in the east, but the part now in the east is later in the west. Thus, it is clear that the power of the mover is said to be in the east by virtue of the inflow of motion, and not through any determination of its substance.
It should also be noted, with respect to the motion of a sphere, that, simultaneously with its motion, it has a kind of immobility:
for the parts are moved as to change of place both as to subject and as to account, but the whole is moved as to change of place in account but not as to subject, as was shown in book 6.
And he mentions here that these two things are attributed to the two principles of the spherical magnitude, for the principle of the motion has its seat on the circumference, while the principle of immobility derives from the fixity of the center.
1170. Then, at “there is a further difficulty” (267b9), he raises a doubt about the foregoing.
First, he raises it;
second, he solves it, at “either such a mover must” (267b11; [1171]).
For he had said previously that an immobile mover can cause continuous motion, and so here (267b9) he subsequently asks whether a moved mover can cause a continuous motion in such a way, namely, that it be truly continuous without any interruption, such as the interruption that occurs when someone pushes a body and then pushes it again. For it is clear that this motion, which is in this way continuous from the standpoint of the mobile, is not truly continuous, because the motions are not continuous, but one follows the other; for the one pushing does not continually push, but at intervals, in such a way that one push is consecutive to another.
1171. Then, at “either such a mover must” (267b11), he resolves this difficulty and shows that no moved mover can cause a continuous motion. For it is necessary to say that a mobile that is seemingly being moved continuously is being moved either immediately through the whole motion by a moved mover, or else through many intermediates, one in contact with the other, as was said with respect to projection. And this division is valid whether the moved mover acts by pushing or pulling or both (as in twirling), as was explained in book 7. Nor does it happen that a thing is moved locally by a moved mover in more than one way per se and not per accidens (for something being carried is being moved per accidens).
And because he had said that, in things that are projected, the mover is constantly different, and this seems to be false because the projected body seems to be continually moved by an air that remains one, he therefore adds, in order to refute this, that it is because air or water are easy to divide that now one and now another (so to speak) mover acts, but yet it acts as if being continually moved, so long as the motion of the projectile lasts; and, although the air seems one, nevertheless it is different through division.
And, in either case—that is, whether the moved mover acts by pushing or by pulling—the motion cannot be one, but must be consecutive for the reason given above, when the motion of projection was discussed, namely, on account of the diversity of movers. What remains, therefore, is that only the motion from an immobile mover can be forever continuous, because this mover remains always similar, according to the same disposition in itself. For that reason, it can maintain itself always and continuously in a similar way with respect to the mobile, namely, so as to move it uniformly.
But it should be noted that the Philosopher here attributes eternity of continuous motion to the immobility of the mover, whereas above he attributed it to its infinite power. For eternity of continuous motion, if regarded with respect to the motion’s repetition, looks to the immobility of the mover, since, if it always remains constant with itself, it can always repeat the same motion. But the infinite power of the mover regards the motion’s whole perpetuity or infinity per se, as was said above.
It should be noted, too, that, because no moved mover can cause a perpetual, continuous motion, he therefore intends to prove in Metaphysics 11 a number of immobile movers according to the number of the heavenly motions, as though that consideration followed upon this.
1172. Then, at “now that these points” (267b17), from the premises already demonstrated, he argues for the main conclusion. And he says that, from the foregoing, it is plainly impossible for the first immobile mover to have any magnitude or to be a body or to be a power residing in a body. For if it had any magnitude, it would be either finite or infinite. But it was proved in book 3, when nature in common was discussed, that an infinite magnitude is not possible. What remains, therefore, is that, if it does have magnitude, it will have a finite magnitude. But that such is not so he proves on the ground that it is impossible for a finite magnitude to possess infinite power, such as the first immobile mover must necessarily have. Therefore, it cannot have a finite magnitude.
But that the first immobile mover must have infinite power he proves from something previously demonstrated: it is impossible for something to be moved for an infinite time by a finite power. Now, the first mover causes a motion that is perpetual and continuous and is one and the same for infinite time, for otherwise, this motion would not be continuous. Therefore, it has infinite power. Thus, it does not have a finite magnitude, and an infinite magnitude is impossible.
It is plain, therefore, that the first mover is indivisible, both as having no part (as even a point is indivisible) and as wholly without magnitude, as though existing outside the genus of magnitude.
And thus does the Philosopher, in his general consideration of natural things, terminate at the first principle of the whole of nature, who is the one above all things, the ever-blessed God. Amen.