Commentary Aristotle Physics
Again, the conclusion seems to be false. For the greater the power of a body, the longer it can endure. If, therefore, the power of no body were infinite, no body could endure to infinity. Now, this is plainly false, both according to his own opinion and according to the tenets of the Christian faith, which posits that the substance of the world will endure to infinity.
It could also be objected that the division and addition that he uses have no correspondence in reality, but since this was sufficiently discussed previously, it can be passed over at the present time.
1148. Thus, answering these doubts in order, it must be said with respect to the first one that the Philosopher in this place does not intend an ostensive demonstration, but one that leads to an impossibility—that is, one in which, since an impossibility follows from something given, that which was given is concluded to be impossible. For it is not true that the first supposition can possibly coexist with the conclusion. Thus, the supposition that there was some power that could remove the genus from a species would allow us to conclude that this power could make man not be animal; but, because this is impossible, the supposition too is impossible. From this, then, it cannot be concluded that it is possible for a power to exist that could make man not be animal. So, too, from the fact that an infinite power exists in a magnitude, it follows of necessity that motion exists in non-time; but since this is impossible, it is impossible for an infinite power to exist in a magnitude; nor can it be concluded from this that it is possible for an infinite power to move in non-time.
1149. To the second doubt, Averroes responds in his commentary at this place that the argument of Aristotle here proceeds from power under the account of its infinity. But finite and infinite belong to quantity, as was proved in book 1. Hence, finite and infinite do not properly belong to a power that is not in a magnitude.
But this answer is contrary both to the intention of Aristotle and to the truth. It is contrary to Aristotle’s intention because, in the preceding demonstration, Aristotle proved that a power that causes motion for an infinite time is infinite, and from this, he later concludes that the power moving the heavens is not a power existing in a magnitude.
It is also against the truth. For since every active power is according to some form, magnitude—and consequently its finiteness and infinity—belong to a power in the way it belongs to form. But magnitude belongs to form both per se and per accidens: it belongs per se according to the perfection of the form, as a whiteness is called “great” even in a small amount of snow, according to the perfection of its proper account; it belongs per accidens according to the extension that a form has in a subject, as a whiteness can be called “great” on account of the size of its surface.
Now, this second magnitude cannot belong to a power not in a magnitude, but the first magnitude certainly can, because the less non-material powers are restricted through union with matter, the more perfect and more universal they are.
But swiftness of motion does not follow upon a magnitude of power that is per accidens by extension with the magnitude of the subject; rather, it follows one that is per se, according to its proper perfection, for the more perfect a thing is in act, the more vehemently is it active. Hence, it cannot be said that a power that does not exist in a magnitude, because it is not infinite with the infinity of magnitude that depends on the magnitude of the subject, therefore cannot cause an increase of swiftness to infinity, that is, move in non-time.
Hence, the same Commentator solves this same difficulty in another way in Metaphysics 11, where he says that a heavenly body is moved by a twofold mover—that is, by a conjoined mover, which is the soul of the heavens, and by a separated mover, which is not moved either per se or per accidens. And, because that separated mover has infinite power, the motion of the heaven acquires from it a perpetual duration; but because the conjoined mover has finite power, the motion of the heaven acquires from it a determinate swiftness.
But even this answer is not sufficient. For since both seem to follow upon an infinite power—namely, that it act for an infinite time (as the preceding demonstration concluded) and that it act in non-time (as this demonstration seems to conclude)—the doubt still remains as to why the soul of the heaven, which acts in virtue of an infinite separated mover, obtains from it the ability to act for an infinite time rather than the ability to act with infinite swiftness, that is, in non-time.
1150. In answer to this doubt, it must be said that every power not in a magnitude acts through intellect, for so the Philosopher proves in Metaphysics 11 that the heaven is moved by its mover. But no power in a magnitude acts as though through intellect, for it was proved in De anima 3 that the intellect is not a power of any body.
Now, this is the difference between an agent that acts through intellect and a material agent: the action of the material agent is proportioned to the nature of the agent, for heating proceeds in proportion to the heat, but the action of an intellectual agent is not proportioned to its nature, but to the form apprehended, for a builder does not build as much as he can, but as much as the account of the conceived form requires.
Consequently, if an infinite power existed in a magnitude, it would follow that the motion produced by it would be in proportion to it, as the present demonstration shows. But, if an infinite power is not in a magnitude, a motion does not proceed from that power in proportion to its power, but according to the account of the thing apprehended, that is, according as it fits the end and nature of the subject.
Another point that should be noted is that, as was proved in book 7, only things having magnitude are moved; hence the swiftness of motion is an effect received from the mover into something having magnitude. But it is plain that nothing having magnitude can receive an effect equal proportionately to the power that is not in a magnitude, because every corporeal nature is related to the incorporeal as a certain particular to what is absolute and universal. Hence, if there is an infinite power that is not in a magnitude, it cannot be concluded that, from it, there results an infinite swiftness in a body that is the effect proportionate to such a power, as has been said.
But there is nothing to prevent a magnitude from receiving the effect of a power existing in a magnitude, because the cause is proportioned to the effect. Hence, if it were supposed that an infinite power existed in a magnitude, it would follow that a corresponding effect would exist in a magnitude, namely, an infinite swiftness. But this is impossible; therefore, the first too is impossible.
1151. From this, the resolution of the third doubt is clear. For to be moved for an infinite time is not repugnant to the account of a moved magnitude, for it befits a circular magnitude, as was shown above. But to be moved with an infinite speed—that is, in non-time—is contrary to the account of a magnitude, as was proved in book 6. Hence, the first mover, possessing infinite power, is, according to Aristotle, the cause of a motion that lasts an infinite time, but not one that has infinite speed.
1152. The fourth doubt is, according to Averroes in his commentary, answered by Alexander’s saying that a heavenly body acquires eternity from a separated mover having infinite power, as well as perpetuity of motion. Hence, just as it is not from the infinity of a heavenly body that it is perpetually moved, so, too, it is not from the infinity of the heavenly body that it endures forever. Both are from the infinity of the separated mover.
Now, Averroes tries to refute this answer, both in his commentary on this passage and in Metaphysics 11, and says that it is impossible for something to acquire perpetuity of existence from another, because it would follow that something perishable in itself could be eternal. Yet something can acquire perpetuity of motion from another, for motion is an act existing in a mobile but caused by a mover. He thus says that, in a heavenly body considered in itself, there is no potency to non-existence, because its substance has no contrary, but there is a potency to rest, because rest is contrary to its motion. And that is why it does not have to acquire perpetuity of existence from another, but must acquire perpetuity of motion from another.
That a heavenly body has no potency to non-existence happens, he says, because a heavenly body is not composed of matter and form as though of potency and act. Rather, says he, such a body is matter existing in act, while its form is its soul, in such a way that it is not constituted in being through the form, but only in motion. Consequently, says he, there is present in it not a potency to existence, but solely a potency to place, as the Philosopher says in Metaphysics 11.
1153. But this solution conforms neither to the truth nor to the intention of Aristotle.
It is not in conformity with truth on a number of counts:
first, because he says that a heavenly body is not composed of matter and form—which is utterly impossible. For it is plain that a heavenly body is something actual, otherwise it would not be in motion—something that is in potency only is not a subject of motion, as was proved in book 6. But whatever is actual is either a subsisting form, as are the separated substances, or has form in something else, which is related to the form as matter and as potency to act. Now, it cannot be said that a heavenly body is a subsistent form, because then it would be understood in act, and neither sensible nor existing under quantity. Therefore, it must be a composite of matter and form, and of potency and act. Consequently, in some sense, it has a potency to non-existence.
But, even if a heavenly body were not a composite of matter and form, it would still be necessary to place in it, in some sense, a potency in respect of existence. For every simple self-subsisting substance necessarily either is its own existence or shares in existence. But a simple substance that is self-subsistent existence itself cannot be but one, just as whiteness, if whiteness were a subsistent being, could be but one. Consequently, every substance after the first simple substance participates in existence. But every participant is composed of the participant and what it participates in, and the participant is in potency to what it participates in. Therefore, in every substance, however simple, other than the first simple substance, there is a potency to existence.