Commentary Aristotle Physics
Lecture 9. Not every mover must be moved
Now, this may come about in either of two ways.
Either the mover moves not on its own account, which is to be referred to something else that moves the mover, or the mover moves on its own account.
Further, in the latter case, either the mover moves the next to last thing or there may be one or more intermediate links.
For instance, the stick moves the stone and is moved by the hand, which again is moved by the man; in the man, however, we have reached a mover that is not so in virtue of being moved by something else.
Now, we say that the thing is moved both by the last and by the first mover in the series, but more strictly by the first, since the first mover moves the last, whereas the last does not move the first, and the first will move the thing without the last, but the last will not move it without the first. For instance, the stick will not move anything unless it is itself moved by the man.
If, then, everything that is in motion must be moved by something and the mover must either itself be moved by something else or not, and in the former case there must be some first mover that is not itself moved by anything else, while in the case of the immediate mover being of this kind there is no need of an intermediate mover that is also moved
(for it is impossible that there should be an infinite series of movers, each of which is itself moved by something else, since, in an infinite series, there is no first term), then if [as was said] everything that is in motion is moved by something and the first mover is moved but not by anything else, it must be moved by itself.
This same argument may also be stated in another way as follows.
Every mover moves something and moves it with something, either with itself or with something else.
For instance, a man moves a thing either himself or with a stick, and a thing is knocked down either by the wind itself or by a stone propelled by the wind.
But it is impossible for that with which a thing is moved to move it without being moved by that which imparts motion by its own agency.
On the other hand, if a thing imparts motion by its own agency, it is not necessary that there should be anything else with which it imparts motion.
Whereas if there is a different thing with which it imparts motion, there must be something that imparts motion not with something else, but with itself, or else there will be an infinite series.
If, then, anything is a mover while being itself moved, the series must stop somewhere and not be infinite. Thus, if the stick moves something in virtue of being moved by the hand, the hand moves the stick; and, if something else moves with the hand, the hand also is moved by something different from itself.
So, when motion by means of an instrument is at each stage caused by something different from the instrument, this must always be preceded by something else that imparts motion with itself.
Therefore, if this last mover is in motion and there is nothing else that moves it, it must move itself.
So, this reasoning also shows that, when a thing is moved, if it is not moved immediately by something that moves itself, the series brings us at some time or other to a mover of this kind.
And, if we consider the matter in yet a third way, we shall get this same result as follows.
If everything that is in motion is moved by something that is in motion, either this being in motion is an accident of the movers in question (such that each of them moves something while being itself in motion, but not always because it is itself in motion) or it is not accidental, but an essential attribute.
Let us consider the former alternative. If, then, it is an accident, it is not necessary that that which causes motion should be in motion; and, if this is so, it is clear that there may be a time when nothing that exists is in motion, since the accidental is not necessary, but contingent.
Now, if we assume the existence of a possibility, any conclusion that we thereby reach will not be an impossibility, though it may be contrary to fact. But the non-existence of motion is an impossibility, for we have shown above that there must always be motion.
Moreover, the conclusion to which we have been led is a reasonable one.
For there must be three things—the moved, the mover, and the instrument of motion.
Now the moved must be in motion, but it need not move anything else.
The instrument of motion must both move something else and be itself in motion (for it changes together with the moved, with which it is in contact and continuous, as is clear in the case of things that move other things locally, in which case, the two things must up to a certain point be in contact).
And the mover—that is to say, that which causes motion in such a manner that it is not merely the instrument of motion—must be unmoved.
Now we have visual experience of the last term in this series, namely, that which has the capacity of being in motion but does not contain a motive principle, and also of that which is in motion but is moved by another and not by itself.
It is reasonable, therefore—not to say necessary—to suppose the existence of the third term also, that which causes motion but is itself unmoved.
So, too, Anaxagoras is right when he says that Mind is impassive and unmixed, since he makes it the principle of motion, for it could cause motion in this sense only by being itself unmoved, and could have supreme control only by being unmixed.
We will now take the second alternative. If the motion is not accidentally in motion, but necessarily—such that, if it were not in motion, it would not move anything—then the mover, insofar as it is in motion, must be in motion in one of two ways. It is moved as that is moved either with the same kind of motion, or with a different kind.
I mean that either what is heating is itself becoming hot, what is making healthy is becoming healthy, and what is causing locomotion is in the process of locomotion, or else what is making healthy is in the process of locomotion, and what is causing locomotion is in the process of increase.
But it is evident that this is impossible.
For if we adopt the first assumption, we have to make it apply within each of the individual species into which motion can be divided.
For instance, we must say that, if someone is teaching some lesson in geometry, he is also in process of being taught that same lesson in geometry, and that, if he is throwing, he is in process of being thrown in just the same manner.
Or if we reject this assumption, we must say that one kind of motion is derived from another: for instance, that what causes locomotion is increase; what causes increase is being altered by something else; and what causes this alteration is the suffering of some other kind of motion.
But the series must stop somewhere, since the kinds of motion are limited.
And if we say that it’s reversible and that what causes alteration is in the process of locomotion, this is the same as saying that what causes locomotion is in the process of locomotion and that one teaching is being taught.
For it is clear that everything that is moved is moved by the mover that is further back in the series as well as by that which immediately moves it; in fact, the earlier mover is that which more strictly moves it.
But this is, of course, impossible, for it involves the consequence that one who is teaching is in process of learning what he is teaching, whereas teaching necessarily implies possessing knowledge, and learning implies not possessing it.
Still more unreasonable is the consequence involved that, since everything that is moved is moved by something that is itself moved by something else, everything that has a capacity for causing motion has as such a corresponding capacity for being moved— that is, it will have the capacity to be moved in the sense in which one might say that what has a capacity for making healthy and exercises that capacity has, as such, a capacity for being made healthy, or that what has a capacity for building has as such a capacity for being built.
It will have the capacity for being thus moved either immediately or through one or more links.
(As it will if, while everything that has a capacity for causing motion has as such a capacity for being moved by something else, the motion that it has the capacity for suffering is not that with which it affects what is next to it, but a motion of a different kind; for instance, that which has a capacity for making healthy might as such have a capacity for learning, but the series could be traced back, as we said before, until, at some time or other, we arrived at the same kind of motion).
Now, the first alternative is impossible, and the second is fantastic: it is absurd that what has a capacity for causing alteration should as such necessarily have a capacity, let us say, for increase.
It is not necessary, therefore, that what is moved should always be moved by something else that is itself moved by something else.
Therefore, there will be an end to the series. Consequently, the first thing that is in motion will derive its motion either from something that is at rest or from itself.
But, if there were any need to consider which of the two (that which moves itself or that which is moved by something else) is the cause and principle of motion, everyone would decide the former.
For that which is itself independently a cause is always prior as a cause to that which is so only in virtue of being itself dependent upon something else that makes it so. We must, therefore, make a fresh start and consider the question: if a thing moves itself, in what sense and in what manner does it do so?
1037. After showing that whatever is moved is moved by another, the Philosopher now begins to show that it is necessary to reach a first immobile mover.
And his treatment is divided into two parts.
In the first, he shows that it is necessary to reach a first that either is immobile or moves itself;
in the second, he shows that, even if a first that moves itself is reached, it is further necessary to reach a first mover that is immobile, at “now, everything that is” (257a33; [1050]).
About the first, he does two things:
first, he shows that it is not possible that things be moved by another to infinity;
second, he shows that not every mover need be moved, at “and, if we consider” (256b3; [1042]).
About the first, he does two things:
first, he explains the proposition by ascending in the order of mobiles and movers;
second, he shows it by descending, at “this same argument” (256a21; [1041]).
About the first, he does two things:
first, he sets out things needed for manifesting his proposition;