Commentary Aristotle Physics
But Aristotle does not have any use for this argument, because someone could say, if he wants, that it happens in some things that they exist at one time and they do not at another without their being generated or ceasing to be, speaking per se, and consequently without their being moved per se. For if something not divisible into parts, namely, something not composed of matter and form, is at one time in a certain way and at another time is not, then necessarily, every such thing—without any self-change—does at one time exist and at another time not exist, as may be said of a point, and of whiteness, and of anything of this sort, for it has been shown in book 6 that whatever is moved can be divided into parts, and in Metaphysics 7 that whatever is generated is composed of matter and form. Such non-divisible things, therefore, are neither generated nor changed per se, but per accidens, when other things are generated or changed.
From this, it is also plain that, if something is moved neither per se nor per accidens, it is eternal, and that, if it is eternal, it is moved neither per se nor per accidens, insofar as it is eternal. If, therefore, it is conceded that it is contingent that something exist at one time and not at another without its being generated or ceasing to be, then let it also be conceded to be contingent that certain immobile moving principles that are yet mobile per accidens exist at one time and do not exist at another. Nevertheless, it is not at all possible that all such principles that are movers and immobile be such that they exist at one time and not exist at another.
1074. Then, at “since there must clearly” (258b22), he proves his proposition. And he says that, if some things that move themselves exist at one time and not at another, then there must be a cause of their generation and ceasing to be, by virtue of which they exist at one time and do not exist at another, because whatever is moved has a cause of its motion. But what exists at one time and not at another, if it is a composite, is generated and ceases to be. Now, a thing that moves itself must possess magnitude, since it is moved, and it has been shown in book 6 that nothing indivisible into parts is moved.
But, from the foregoing, it cannot be held that it is necessary for the mover to have magnitude, and thus it is not moved per se, if it exists at one time and does not exist at another. But, if there is a cause of the generation and corruption of things that move themselves, then there must also be a cause to account for their generation and corruption being continued forever.
But it cannot be said that the cause of this continuity is one of those immobiles that do not always exist, nor can it be said that the causes of the eternal generation and corruption of some things that move themselves are certain immobile movers that do not always exist and that the causes of other such generations and corruptions are certain other such immobile movers. And he explains this when he says that not one, nor all of them, can be the cause of this continuous and eternal generation.
That one of them cannot be the cause he thus proves. What does not exist forever cannot be the cause of what is always, perpetual, and necessary. That all cannot be the cause he proves by the fact that all such perishable principles, if generation is perpetual, are infinite and do not all exist at once. But it is impossible for one effect to depend on an infinitude of causes.
And again, things that do not exist at once cannot be the cause of one thing, although it could be said that, when things do not exist all at once, some dispose and some cause, as is plain with respect to drops that fall successively and wear away a stone. But, if a number of things are a direct cause of anything, they must exist all together.
Accordingly, it is manifest that, if there are a million principles that are movers and immobile, and if there are many things that move themselves, of which some perish and others come to be, and among these, some are mobile and some movers, nevertheless there must be something above all of them that, by its power, contains all the things that are generated and perish in the above-mentioned way and that would be the cause of the continual change affecting them by which they sometimes are and sometimes are not and through which these latter are the causes of coming to be and of motion for others, with these others being the cause for yet others.
For every generator is a cause of generation to the thing generated, but it is from some imperishable first principle that perishable generators possess the characteristic of being causes of generation. If, therefore, the motion through which some things at one time exist and at another do not is perpetual, as has been shown above, and a perpetual effect cannot exist except from a perpetual cause, then, necessarily, the first mover is perpetual, if it is one; and if there are more than one first movers, they too are perpetual.
1075. Then, at “we ought, however” (259a8), he shows that one perpetual principle ought to be posited rather than many. And he says that, just as finite principles ought to be preferred to infinite ones, so should one first principle be preferred rather than many. For if the same effects happen or follow from positing finite principles as from positing infinite principles, one should assume that the principles are finite rather than infinite, for in things that are according to nature, the preference must be given to what is better, if it is possible, because things that are according to nature are disposed the best. Now, a finite principle is better than an infinite one, and one is better than many. But one first immobile principle, if it is perpetual, is sufficient for causing the perpetuity of motion. Therefore, many first principles should not be posited.
1076. Then, at “the following argument” (259a13), he concludes from the foregoing that it is necessary that there be one first mover that is imperishable. And, although this seems to be sufficiently proved from the foregoing, yet someone could cavil that the cause of the continuity of generation is a perpetual first self-mover whose own mover is not perpetual and one, but is rather diverse movers, some of which cease to be and some of which come to be. But he intends to dismiss this, for if motion is perpetual, as he had proved above, then necessarily the motion of the first self-mover, which is posited as the cause of the entire perpetuity of motion, is eternal and continuous. For if it were not continuous, it would not be eternal. However, what is successive is not continuous, but in order that a motion be continuous, it must be one; and in order to be one, it must be from one mover and in one mobile. But, if the mover is different, the motion will not be a whole continuous motion, but a successive one. Therefore, it is absolutely necessary that the first mover be one and perpetual. But an immobile mover that is moved per accidens is not perpetual, as has been said above. It remains, therefore, that the first mover is utterly immobile, both per se and per accidens2245.
Lecture 13. The first mover is eternal and immobile, while the first motion is eternal
Moreover, a conviction that there is a first unmoved something may be reached not only from the foregoing arguments, but also by considering again the principles operative in movers.
Now, it is evident that, among existing things, there are some that are sometimes in motion and sometimes at rest.
This fact has served above to make it clear that it is not true either that all things are in motion or that all things are at rest or that some things are always at rest and the remainder always in motion. On this matter, proof is supplied by things that fluctuate between the two and have the capacity of being sometimes in motion and sometimes at rest.
The existence of things of this kind is clear to all, but we wish to explain also the nature of each of the other two kinds and show that there are some things that are always unmoved and some things that are always in motion.
In the course of our argument directed to this end, we established the fact that everything that is in motion is moved by something, and that the mover is either unmoved or in motion, and that, if it is in motion, it is moved either by itself or by something else and so on throughout the series; and so we proceeded to the position that the first principle that directly causes things that are in motion to be moved is that which moves itself, and the first principle of the whole series is the unmoved.
Further, it is evident from actual observation that there are things that have the characteristic of moving themselves, such as the animal kingdom and the whole class of living things.
This being so, then, the view was suggested that perhaps it may be possible for motion to come to be in a thing without having been in existence at all before, because we see this actually occurring in animals: they are unmoved at one time and then again they are in motion, as it seems.