Commentary Aristotle Physics
Lecture 12. The first mover is immobile and one
Since there must always be motion without intermission, there must necessarily be something—one thing, or maybe a plurality—that first imparts motion, and this first mover must be unmoved.
Now, the question whether each of the things that are unmoved but impart motion is eternal is irrelevant to our present argument.
But there must necessarily be some such thing that, while it has the capacity of moving something else, is itself immobile with respect to any change from without, which can affect it neither in an unqualified sense nor in an accidental one.
If anyone likes, let us suppose that, in the case of certain things, it is possible for them at different times to be and not to be, without any process of generation and corruption (in fact, it would seem to be necessary, if a thing that has not parts at one time is and at another time is not, that any such thing should, without undergoing any process of change, at one time be and at another time not be).
And let us further suppose it possible that some principles that are unmoved but capable of imparting motion at one time are and at another time are not. Even so, this cannot be true of all such principles, since there must clearly be something that causes things that move themselves at one time to be and at another not to be. For since something not divisible into parts cannot be in motion, that which moves itself must as a whole have magnitude, though nothing that we have said makes this necessarily true of every mover.
So, the fact that some things become and others perish, and that this is so continuously, cannot be caused by any one of those things that, though they are unmoved, do not always exist: nor again can it be caused by any of those that move certain particular things while others move other things.
The eternity and continuity of the process cannot be caused either by any one of them singly or by the sum of them, because this causal relation must be eternal and necessary, but the sum of these movers is infinite and they do not all exist together.
It is then clear that, though there may be countless instances of the corruption of some principles that are unmoved but impart motion, and though many things that move themselves perish and are succeeded by others that come into being, and though one thing that is unmoved moves one thing while another moves another, there is nevertheless something that comprehends them, and that as something apart from each one of them and which is the cause of the fact that some things are and others are not and of the continuous change, and this causes the motion of the other movers, while they are causes of the motion of others.
Thus, motion being eternal, the first mover, if there is but one, will be eternal also; if there are more than one, there will be a plurality of such eternal movers.
We ought, however, to suppose that there is one rather than many, and a finite rather than an infinite number.
When the consequences of either assumption are the same, we should always assume that things are finite rather than infinite in number, since, in things constituted by nature, that which is finite and that which is better ought, if possible, to be present rather than the reverse.
Here it is sufficient to assume only one mover, the first of unmoved things, which, being eternal, will be the principle of motion to everything else.
The following argument also makes it evident that the first mover must be something that is one and eternal. We have shown that there must always be motion. That being so, motion must also be continuous, because what is always is continuous, whereas what is merely consecutive is not continuous.
But, further, if motion is continuous, it is one; and it is one only if the mover and the moved that constitute it are each of them one, for in the event of a thing’s being moved now by one thing and now by another, the whole motion will not be continuous, but successive.
1069. Having shown that, in things moved by another, there is no proceeding to infinity, but a first must be reached that is either immobile or a mover of self, and having shown that, of a thing that moves itself, one part is an immobile mover, and that, consequently, in either case, there is a first mover that is immobile, and because, among self-movers that exist among us (namely, perishable animals), it happens that the motion-causing part in the thing that moves itself—namely, the soul—is perishable and moved per accidens, the Philosopher now wishes to show here that the first mover is imperishable and is not moved either per se or per accidens.
About this, he does two things:
first, he proposes what he intends;
second, he proves it, at if anyone likes, let us suppose (258b16; [1072]).
About the first, he does three things:
first, he reviews what has been previously shown;
second, he passes over something that seemed useful for his proposition, at now, the question (258b12; [1070]);
third, he explains his proposition, at but there must necessarily (258b13; [1071]).
He says first (258b10) that it was shown above that motion always exists and never fails. And, since all motion is from a mover, and since in movers there is no proceeding to infinity, it is necessary that there be a first mover. And, since it has not yet been proved that the first mover is one, he accordingly lets it remain doubtful whether it is one or many. Further, it has been shown that the first mover is immobile, whether, by ascending from moved to movers, one immediately reaches a first immobile mover, or whether what is reached is a first mover that moves itself, one part of which is an immobile mover.
1070. Some have opined that all moving principles in things that move themselves are imperishable, for Plato posited all the souls of animals to be perpetual. And, if this opinion were true, Aristotle would have his proposition clinched at once, so far as the first mover’s being eternal is concerned. But the opinion of Aristotle is that, among the parts of the soul, only the intellect is imperishable, even though other parts of the soul are movers.
Consequently, he passes over this at “now, the question” (258b12), where he says that, as far as the present argument is concerned, it is of no moment whether each of the principles that move themselves and are immobile is imperishable, even though some have posited this by positing that all souls are imperishable. And he says that this does not affect the present argument, because he will prove his proposition without using this supposition.
1071. Then, at “but there must necessarily” (258b13), he explains what he intends to prove. And he says that, by considering the things that follow, it can be shown that, even though not every immobile mover is imperishable, there must be something immobile in such a way that it is in no way moved from without, either absolutely or per accidens, and yet is a mover of something else.
When he says, “immobile with respect to any change from without,” he does not mean to exclude a motion—that is, an operation—that is in the one operating in the sense that to understand is called a “motion,” and in the sense that the appetite is moved by the desirable object. A motion of this sort is not excluded from the first mover that Aristotle is discussing.
1072. Then, at “if anyone likes, let us suppose” (258b16), he proves what he had said, namely, that there exists a first mover that is eternal and entirely immobile.
First, he proves this through self-movers that at one time exist and at another time do not;
second, he proves through moving principles that sometimes are causing motion and sometimes not, at moreover, a conviction (259a21; [1077]).
About the first, he does three things:
first, he shows that there must be a first mover that is eternal;
second, he shows that such a mover should be one rather than many, at we ought, however (259a8; [1075]);
third, he shows both at once—that is, that there is one first mover, and that it is eternal—at “the following argument” (259a13; [1076]).
About the first, he does two things: first, he rejects an argument by which some could try to prove this proposition;
second, he goes on to explain his proposition, at since there must clearly (258b22; [1074]).
1073. Now, someone could proceed as follows (258b16). Whatever cannot be at one time and not be at another is eternal; but the first mover, since it is immobile (as has been shown above), cannot be at one time and not be at another time, for whatever is such is generated and ceases to be, which involves its being moved. Therefore, the first mover is eternal.