Commentary Aristotle Physics
Lecture 6
It cannot be said that some things are always at rest and all other things are always moved
Nor again can it be that some things are always at rest, others always in motion, and nothing sometimes at rest and sometimes in motion. This theory must be pronounced impossible on the same grounds as those previously mentioned: we see the above-mentioned changes occurring in the case of the same things.
We may further point out that the defender of this position is fighting against the obvious, for on this theory there can be no such thing as increase;
nor can there be any such thing as motion by force, if it is impossible that a thing can be at rest before being set in motion unnaturally. This theory, then, does away with generation and corruption.
Moreover, motion, it would seem, is generally thought to be a sort of generation and corruption, for this to which a thing changes comes to be, or in which it comes to be, and that from which a thing changes ceases to be, or there ceases to be occupancy of it. It is clear, therefore, that there are cases of occasional motion and occasional rest.
We have now to take the assertion that all things are sometimes at rest and sometimes in motion and to confront it with the arguments previously advanced.
We must take our start, as before, from the possibilities that we distinguished just above. Either all things are at rest, or all things are in motion, or some things are at rest and others in motion.
And if some things are at rest and others in motion, then it must be that either all things are sometimes at rest and sometimes in motion, or some things are always at rest and the remainder always in motion, or some of the things are always at rest and others always in motion while yet others, again, are sometimes at rest and sometimes in motion.
Now, we have said before that it is impossible that all things should be at rest. Nevertheless, we may now repeat that assertion.
We may point out that, even if it is really the case, as certain persons assert, that the existent is infinite and motionless, it certainly does not appear to be so if we follow sense perception, since many things that exist appear to be in motion.
Now, if there is such a thing as false opinion or opinion at all, there is also motion, and similarly if there is such a thing as imagination, or if it is the case that anything seems to be different at different times, for imagination and opinion are thought to be motions of a kind.
But to investigate this question at all—to seek a reasoned justification of a belief with regard to which we are too well off to require reasoned justification—implies bad judgment of what is better and what is worse, what commends itself to belief and what does not, what is ultimate and what is not.
It is likewise impossible that all things should be in motion or that some things should be always in motion and the remainder always at rest. We have sufficient ground for rejecting all these theories in the single fact that we see some things that are sometimes in motion and sometimes at rest.
It is evident, therefore, that it is no less impossible that some things should be always in motion and the remainder always at rest than that all things should be at rest or that all things should be in motion continuously.
It remains, then, to consider whether all things are so constituted as to be capable both of being in motion and of being at rest, or whether, while some things are so constituted, some are always at rest and some are always in motion; for it is this last view that we have to show to be true.
1014. Having disposed of two members of the foregoing division, the Philosopher now rejects a third, that in which it was posited that things are divided into two dispositions only, in such a way that some things are always at rest and others always in motion, and there is not a third class of things that are sometimes in motion and sometimes at rest.
He rejects this in two ways.
He does this first (254a3) in the same way that he rejected the two previous positions, on the ground that they are contrary to sense observation. For we see by the senses not only that some things are in motion (which destroys the first position, namely, of those who posit all things to be always at rest) and that some are at rest (by which is destroyed the second position, that all things are always in motion) but also that the aforementioned changes or variations from motion to rest, and from rest to motion, occur in the same things. This shows that there are some things that are sometimes moved and sometimes at rest.
1015. In a second way, at “we may further point out” (254a8), he rejects the same opinion on the ground that the one who would engender this doubt would resist what is evident in nature.
In the first place, it would deny the motion of growth, for we see that growth takes place in things that are not always growing, because, were they always growing, they would be tending not to a definite quantity but to the infinite.
In the second place, it would deny forced local motion, for a motion is not by force unless something is moved outside of its nature when previously it was naturally at rest; for a forced motion is nothing more than a departure from natural rest. If, therefore, nothing at rest can be moved, it will follow that what is naturally at rest cannot later be moved by force.
In the third place, generation and ceasing to be would be excluded by this opinion. For the former is a change from non-being to being, and the latter from being to non-being. Therefore, in order that a thing cease to be, it ought previously to have been existing for a time, and in order that a thing be generated, it ought previously not to have been existing for a time. But whatever is a being or a non-being for some time is at rest (where rest is taken in a very general sense). If, therefore, nothing at rest can be moved, it follows that nothing that does not exist for some time can be generated, and that nothing that exists for a time can cease to be.
In the fourth place, this position destroys all motion universally, because every motion involves generation and ceasing to be either absolutely or in a qualified sense. For what is being moved toward something as toward a terminus is being made this, so far as alteration and growth are concerned, or being made to be in which, so far as local motion is concerned; for example, what is being changed from black to white, or from small to large, becomes white or large, but whatever is being moved to a place comes to exist in that place. But, when something is changed from its terminus from which, then, when it is a case of alteration and growth, a this has ceased to be, and when it is a case of local motion, a there has ceased to be. Therefore, because in every motion there is generation and ceasing to be, this position consequently rejects all motion.
Because such things are impossible, it becomes clear that some things are being moved, but not always, and that some things are at rest not always, but sometimes.
1016. Then, at “we have now to take” (254a15), he studies the other two members of his division.
First, he reveals his intention;
second, he pursues it, at “now, of things that cause motion” (254b7; [1021]).
About the first, he does three things:
first, he shows to which opinion the fourth member pertains;
second, he summarizes what has been said in this chapter, at “we must take our start” (254a16; [1017]);
third, he states what remains to be said, at “it remains, then” (254b4; [1020]).
He therefore says first (254a15) that to posit that all things are sometimes at rest and sometimes in motion pertains to the ancient arguments that we touched upon in discussing the eternity of motion. For Empedocles seems to be the chief protagonist of this opinion that all things are at some times moved by friendship and by discord and in the meantime are at rest.
1017. Then, at “we must take our start” (254a16), he sums up what has been said in this chapter.
First, he recalls the divisions previously made;
second, he recalls the rejection of the first member, which posited all things at “now, we have said” (254a23; [1018]);
third, he recalls the rejection of the other two members, at “it is likewise impossible” (254a33; [1019]).
He first says, therefore (254a16), that, in order to make clearer the intention of what follows, we must begin with what has just been determined and use the same principle as before: beings must maintain themselves in one of three dispositions, that is, either that all are at rest or all in motion or some at rest and some in motion.
And this third is again divided into three members, for if all things are such that some are at rest and others in motion, then necessarily, all must be at one time at rest and at another in motion, or some are always at rest and others always in motion—or to these two a third member may be added, namely, that there are others of which some are at rest not always, but sometimes, while the others are in motion sometimes but not always.
1018. Then, at “now, we have said” (254a23), he rejects the first member and says that it was said above that it is not possible for all things to be always at rest; but something else must now be added.
And he says two things against this position.
First, some motion must be posited at least in the soul. For, should anyone want to say that, according to truth, it is a fact that nothing is being moved (as the followers of Melissus did, who posited that being is infinite and immobile), yet it is also a fact that this does not appear to be so according to sense, for many things appear to the senses to be moving. If, therefore, anyone declares as false the opinion by which we believe that some things are in motion, it still follows that motion exists. For if there is false opinion, there is motion; and universally, if there is opinion, there is motion; and, likewise, if there is imagining, there is motion. The reason is that imagining is a motion of the sensitive part and is produced by the sense in act. Opinion also is a certain motion of the reason and proceeds from several acts of reasoning. But it follows even more strongly that there is motion in opinion and imagining if things appear to be this at one time and that at another. This happens when things at one time seem to us to be at rest and at another time not to rest. Thus, it entirely follows that motion exists.
He says, second, against the opinion at issue, that to have the intention of destroying this opinion and to look for an argument to prove those things that we ought to hold in a respect surpassing the need for proof, since they are accepted as self-evident, I say is no different from judging poorly between what is better and what is worse in morals, or between what is credible and incredible in logical matters, and between a principle and a non-principle in matters of demonstration. For whoever looks for arguments to prove things that are self-evident and, consequently, held as principles, does not recognize them for principles so long as he intends to prove them through other principles. Likewise, it seems that he does not recognize what is credible and what is incredible, because he is trying to prove what is per se credible through something else, as though it were not per se credible. Nor does he seem capable of distinguishing between the better and the worse who tries to prove the more evident by means of the less evident. But it is self-evident that some things are in motion. Therefore, we should not address ourselves to trying to prove this by arguments.
1019. Then, at “it is likewise impossible” (254a33), he rejects two more members of his original division.
And he says that, just as it is impossible for all things to be always at rest, so too is it impossible for all things to be always in motion, or for some things to be always in motion and some always at rest such that nothing is sometimes in motion and sometimes at rest. Against all this, sufficient credence arises from one medium: the fact that we see that some things are sometimes in motion and sometimes at rest. Hence, it is clear that it is impossible to say that all things are continually at rest—which was the first member—or that all things are continually in motion—which was the second member—or that some are always in motion and the remainder always at rest without any mediate possibility.
1020. Then, at “it remains, then” (254b4), he shows what is left to be said, and he concludes from the foregoing that, since three members of the division cannot stand, what remains is to consider which of the other two is the truer—whether all things are capable of both motion and rest, or whether some are capable of both motion and rest while still others are always at rest and others always in motion. This last is what we intend to demonstrate. In this way, it will be shown that the first motion is eternal and the first mover immobile.