Commentary Aristotle Physics
That is the reason that animals are not always moved by themselves, for with respect to any animal moving itself, there is found some previous mover that is being moved and causes motion. For if it were entirely immobile, it would always maintain itself in the same way in causing motion, and consequently, the motion also of the animal would be perpetual. But, because this extrinsic mover that moves animals is itself moved, it does not always move in the same way.
Hence, neither do animals always move themselves in the same way, for in all these things, the first mover that is the cause of the animal’s moving itself, such as the soul, causes motion in such a way that it is itself being moved not per se, but per accidens, for the body is changed with respect to place, and when the body has been changed, that which exists in the body, namely, the soul, is also changed per accidens. And, thus, the whole that moves itself is changed of necessity, such that it does not maintain itself in the same disposition for causing motion.
1081. Then, at “hence, we may confidently” (259b20), he proves his proposition from the foregoing.
First, he proves that the first mover is immobile;
second, that the first motion is perpetual, at and, further, if there (259b32; [1083]).
About the first, he does two things:
first, he proves the proposition;
second, he dismisses an objection, at we must distinguish (259b28; [1082]).
He says first (259b20) that, from the foregoing, we can know that, if some principle is an immobile mover nevertheless moved per accidens, it cannot cause a continuous and perpetual motion. For the reason assigned for saying that animals do not always move is that they are moved per accidens. But it has been shown above that the motion of the universe must be continuous and perpetual. Therefore, it is necessary that the first moving cause in the whole universe be immobile in such a way as not to be moved even per accidens.
But, as was said above, a motion that is immortal and unceasing ought to be found in natural things, and the whole being, that is, the disposition of this universe, should be maintained in its disposition and in the same state. For from the immobility of the principle that is posited as remaining immobile, it follows that the entire universe has an eternal permanence, insofar as it is joined to the first immobile principle and receives an influence from it.
1082. Then, at “we must distinguish” (259b28), he excludes an objection. For he had said that, if a mover is moved per accidens, it does not move with a sempiternal motion. Now, this seems to give rise to an objection, because, according to his position, the motions of the inferior orbs (such as the sun and moon and other planets) are eternal, and yet their movers seem to be moved per accidens, if we follow what he had just said. For he said that the reason that the soul of an animal is moved per accidens is that the animal’s body is moved by an external principle, which is not from the soul. In like manner, it appears that the orb of the sun is moved by some other motion as though carried along by the motion of the first orb, insofar as it revolves from east to west; this is not the way it is moved by its proper mover, but contrariwise, from west to east.
He dismisses this objection, saying that being moved per accidens can be attributed to something either with respect to itself or with respect to something else, and this is not the same. Now, being moved per accidens can be attributed to the movers of the orbs of the planets not in the sense that these movers are moved per accidens, but that the orbs moved by them are moved per accidens in being influenced by the motion of the superior orb. And this is what he says: to be moved per accidens by something else is attributed to certain principles of heavenly motions in the case of the movers of the orbs that are moved by more than one motion, namely, by their own and by that of the superior orb.
But the other case—namely, that a thing be moved per accidens with respect to itself—is found only in perishable things, as in the souls of animals. The reason for this diversity is that the movers of the superior orbs are not made to exist through being united to bodies, and their connection with the latter is unvarying; therefore, although the bodies of the orbs are moved, the motors are not moved per accidens. But the souls that move animals depend for their existence on being united to their bodies, and they are connected in a way subject to variation, and accordingly, as the bodies are affected by change, the souls themselves are said to be changed per accidens.
1083. Then, at “and, further, if there” (259b32), he proves that the first motion is perpetual. And he does this with two arguments, the first of which depends on the foregoing. A motion that is not perpetual is found to be from a mover that is moved per se or per accidens, as is evident from above. Since, therefore, the first mover is immobile and perpetual, and is moved neither per se nor per accidens, then, necessarily, the first mobile, which is moved by this utterly immobile mover, is moved with a perpetual motion.
Now, it should be noted that he above proved the immobility of the first mover by means of the perpetuity of motion, shown above. Here, on the contrary, through the immobility of the first mover, he proves the perpetuity of motion. But this would be arguing in a circle if the same motion were meant in both arguments.
Hence, it must be said that, above, he proves the immobility of the first mover from the perpetuity of motion in general; that is why he said that, among the things that exist, there is an unceasing and immortal motion. But here, through the immobility of the first mover he proves the perpetuity of the first motion. From this, it is plain that what the Commentator says is false, namely, that, in the beginning of book 8, Aristotle proved that the first motion is perpetual.
1084. The second argument is given at “indeed, this is clear also” (260a1), and it is taken from the perpetuity of generation. And he says that the first motion is perpetual for another reason, namely, that the only way temporal generation and ceasing to be and changes of this sort can exist is that something move and be moved, for it has been proved above that every change is caused by some mover. Therefore, coming to be and ceasing to be and change of this kind ought to be from a mover. But they cannot be immediately from the immobile mover, because the immobile will always cause the same motion and in the same way, for its relation to the mobile is not variable; and, given a relation between mover and moved that remains the same, the motion remains always the same. However, coming to be and ceasing to be are not always in the same state, but at one time something is generated and at another it ceases to be. Therefore, these changes are not immediately from the immobile mover, but from a mobile mover.
Now, whatever is moved by a moved mover that in turn is moved by the immobile mover can retain perpetuity in spite of the alternation of diverse motions, because, since the mobile mover stands in varying relation to the things moved, it will not always cause the same motion. Rather, since it occupies differing positions (if moved with local motion), or assumes differing forms (if moved with a motion of alteration), it will produce a contrary motion in other things and will cause them to be at one time at rest and at another time in motion. He says contrary positions or forms because it has not yet been proved by what form of motion the first mobile is moved; but he will inquire into this later.
Thus, therefore, insofar as it is moved, it is a cause of the diversity of motions; but insofar as it is moved by the immobile mover, it is the cause of the perpetuity in this diversity of changes. Therefore, the very perpetuity of generation shows that the first motion is perpetual and brought about by the immobile mover.
But it should be understood that these arguments by which Aristotle tries to prove that the first motion is perpetual do not conclude of necessity, for it can happen without any change in the first mover that it not always cause motion, as was shown above in the beginning of this book 8.
1085. Then, at “the foregoing argument” (260a11), he draws a conclusion that he left unsettled above, namely, why some things are always in motion and some not always. And he says that the cause of this is now plain from what has gone before. Things that are moved by an immobile and eternal mover are always in motion; things that are moved by a changed mover are not always in motion—for the immobile, as previously stated, since it remains absolutely alike and in the same state, will cause a motion that is one and simple.