Commentary Aristotle Physics
Lecture 14. Local motion is the first motion
This matter will be made clearer, however, if we start afresh from another point. We must consider whether it is or is not possible that there should be a continuous motion, and if it is possible, which this motion is, and which is the primary motion. For it is plain that, if there must always be motion and a particular motion is primary and continuous, then it is this motion that is imparted by the first mover, and so it is necessarily one and the same and continuous and primary.
Now, of the three kinds of motion that there are—motion in respect of magnitude, motion in respect of passion, and motion in respect of place—it is this last, which we call locomotion, that must be primary.
This may be shown as follows. It is impossible that there should be increase without the previous occurrence of alteration, for that which is increased, although in a sense it is increased by what is like itself, is in a sense increased by what is unlike itself.
Thus, it is said that contrary is nourishment to contrary, but growth is effected only by things becoming like to like. There must be alteration, then, in that there is this change from contrary to contrary.
But the fact that a thing is altered requires that there should be something that alters it—for instance, something that makes the potentially hot into the actually hot.
So, it is plain that the mover does not maintain a uniform relation to it, but is at one time nearer to what is altered and at another farther from it, and we cannot have this without locomotion.
If, therefore, there must always be motion, there must also always be locomotion as the primary motion, and if there is a primary as distinguished from a secondary form of locomotion, it must be the primary form.
Again, all passions have their origin in condensation and rarefaction; thus, heavy and light, soft and hard, and hot and cold are considered to be forms of density and rarity. But condensation and rarefaction are nothing more than combination and separation, processes in accordance with which substances are said to become and perish; and in being combined and separated, things must change in respect of place. And, further, when a thing is increased or decreased, its magnitude changes in respect of place.
Again, there is another point of view from which it will be clearly seen that locomotion is primary. As in the case of other things, so too in the case of motion, the word “primary” may be used in several senses.
A thing is said to be prior to other things when, if it does not exist, the others will not exist, while it can exist without the others; and there is also priority in time and priority according to substance. Let us begin, then, with the first sense.
Now, there must be motion continuously, and there may be continuously either continuous motion or successive motion—the former, however, in a higher degree than the latter. Moreover, it is better that it should be continuous rather than successive motion, and we always assume the presence in nature of the better, if it be possible.
Since, then, continuous motion is possible (this will be proved later; for the present let us take it for granted) and no other motion can be continuous except locomotion, locomotion must be primary. For there is no necessity for the subject of locomotion to be the subject either of increase or of alteration, nor need it become or perish. On the other hand, there cannot be any one of these processes without the existence of the continuous motion imparted by the first mover.
Second, locomotion must be primary in time, for this is the only motion possible for things.
It is true indeed that, in the case of any individual thing that has a generation, locomotion must be the last of its motions, for after its generation, it first experiences alteration and increase, and locomotion is a motion that belongs to such things only when they are perfected.
But there must previously be something else that is in process of locomotion to be the cause even of the generation of things that become without itself being in process of generation (as, for instance, the begotten is preceded by what begot it).
Otherwise, generation might be thought to be the primary motion on the ground that the thing must first become. But, though this is so in the case of any individual thing that becomes, nevertheless, before anything becomes, something else must be in motion, not itself generation, but being, and before this, there must again be something else.
And since generation cannot be primary—for if it were, everything that is in motion would be perishable—it is plain that no one of the motions next in order can be prior to locomotion.
By “the motions next in order,” I mean increase and then alteration, decrease, and corruption. All these are posterior to generation, and consequently, if not even generation is prior to locomotion, then no one of the other processes of change is so either.
Third, that which is in process of generation appears universally as something imperfect and proceeding to its principle, and so what is posterior in the order of generation is prior in the order of nature.
Now, all things that go through the process of generation acquire locomotion last. It is this that accounts for the fact that some living things—for instance, plants and many kinds of animals—are entirely without motion owing to lack of the requisite organ, while others acquire it in the course of their being perfected.
Therefore, if the degree in which things possess locomotion corresponds to the degree that they comprehend nature, then this motion must be prior to all others in respect of perfection of existence.
And not only for this reason, but also because a thing that is in motion loses its essential character less in the process of locomotion than it does in any other kind of motion. It is the only motion that does not involve a change of being in the sense in which there is a change in quality when a thing is altered and a change in quantity when a thing is increased or decreased.
Above all, it is plain that this motion—motion in respect of place—is what is in the strictest sense produced by that which moves itself.
But it is the self-mover that we declare to be the first principle of things that are moved and impart motion and the primary source to which things that are in motion are to be referred. It is clear, then, from the foregoing arguments, that locomotion is the primary motion.
1086. After showing that the first mover is immobile and that the first motion is perpetual, the Philosopher here begins to show which motion is the first and what kind of being the first mover is.
And it is divided into two parts:
in the first, he shows which is the first motion;
in the second, what kind of being the first mover is, at we have now to assert (266a10; [1141]).
About the first, he does two things:
first, he states his intention;
second, he carries out his proposal, at now, of the three (260a26; [1087]).
He says first that, in order that the consideration of the foregoing be more certain, we must begin from another starting point and consider whether there is any motion that may be infinitely continuous (and, if so, which it is), and which is the first of all motions.
And, lest anyone should think that the one that may be continuous and the one that is first are two different motions, in order to exclude this, he adds that it is plain that, since it is necessary that motion should always exist and that the first should be forever continuous (for it is caused by the first immobile mover), then it is necessarily one and the same motion that is eternally continuous and that is first.
1087. Then, at “now, of the three” (260a26), he proves the proposition:
first, with arguments;
second, by referring to the sayings of the ancients, at as to locomotion being the primary (265b17; [1139]).
About the first, he does two things:
first, he shows that local motion is the first;
second, he shows which local motion, at we have now to show (261a28; [1097]).
The first he proves in three ways:
first, through the properties of motions;
second, through the difference between prior and subsequent, at again, there is another (260b15; [1090]);
third, by reason of the order of mobiles, at above all, it is plain (261a23; [1096]).
1088. With respect to the first, he gives two arguments.
In regard to the first of these, he proceeds thus.
First, he proposes what he intends and says that, since there are three species of motion—one with respect to quantity that is called growth and decrease, another with respect to passible quality that is called alteration, and a third with respect to place that is called local motion—the last one must be the first of all.
Second, he proves this on the ground that it is impossible for growth to be the first motion, for growth cannot take place unless an alteration precedes it, because that by which something is increased is somehow dissimilar and somehow similar to it. That it is dissimilar is plain, because that by which something is increased is food, which is in the beginning contrary to what is nourished on account of the diversity of disposition. But, when it is added and causes increase, it is necessarily similar to it. Now the transition from dissimilar to similar does not take place except through alteration. Therefore, it is necessary that, before growth, there must occur alteration through which food is changed from one contrary disposition to the other.
Third, he shows that, before every alteration, there is a previous local motion, for if something is altered, it is necessary that there be something causing alteration that makes the potentially hot come to be actually hot. But, if this cause of alteration were always in the same way near at an equal distance to the thing altered, then it would not make it any hotter now than it was previously.
Therefore, it is plain that the mover in alteration does not remain the same distance from what is altered, but is at one time closer and at another time farther away—and this cannot happen without a change of place. If, therefore, motion must always exist, then local motion must always exist, since it is the first of all motions. And, if one local motion is prior to all other local motions, then, necessarily, if the foregoing is true, this first motion must be eternal.
1089. He gives the second argument at “again, all passions” (260b7). Alteration, as was proved in book 7, occurs with respect to passions and passible qualities, among which, according to the opinions of the ancients, density and rarity seem to be a principle, because the heavy and the light, the soft and the hard, and the hot and the cold seem both to result from the dense and the rare and to be distinguished by reason of them (for among the elements, the dense are found to be the heavy and the cold, and the rare are found to be the hot and the light). Now, this opinion is true to a certain extent if the passible qualities be arranged according to their proximity to the material principle, for the rare and the dense seem especially to pertain to matter, as is clear from what was said in book 4. But density and rarity seem to be instances of commingling and separation, according to which the ancient philosophers explained the generation and ceasing to be of substances. Aristotle uses this opinion as probable before manifesting the truth about generation and ceasing to be in De generatione et corruptione. But things commingled and separated seem by that very fact to be changed with respect to place. Hence, change of place is a principle of alteration.
But it should be noted that, although the commingling and separation that affect bodies actually existing pertain to local motion, yet the commingling and separation according to which the same matter is contained under larger or smaller dimensions do not pertain to local motion, but to the motion of alteration. And it was in this sense that, in book 4, Aristotle explained the account of the dense and of the rare. But here he is speaking according to what is probable according to the opinion of other philosophers.
Yet, just as local motion is required for alteration, so also is it required for growth. For it is necessary that the magnitude of what is increased or decreased be moved with respect to place, because what is increased expands into a larger place, while what decreases shrinks into a lesser place. Therefore, in this way, it is plain that local motion is naturally prior to both alteration and growth.
1090. Then, at “again, there is another” (260b15), he proves the same by distinguishing the prior and the posterior. And he says that, from this consideration, it will be clear that change of place is the first of motions, for just as in other things, so too in motion, one thing is said to be prior to another in various ways.
For in one way, something is said to be prior in the sense that, if it does not exist, neither do the other things, while it itself can exist without the others, as one is prior to two because two cannot exist unless there is one, but one can exist even if there are not two.
In a second way, something is said to be prior in time (namely, in the past) when something is more distant from the present now, or in the future, when something is closer to the present, as was said in book 4.
Third, something is said to be prior according to substance, that is, with respect to what completes a substance, as act is prior to potency, and the perfect to the imperfect.
1091. Second, at “now, there must be motion” (260b19), he proves that local motion is the first among the three above-mentioned kinds of motion:
first, as to the first;
second, as to the second, at second, locomotion (260b29; [1092]);
third, as to the third, at third, that which is (261a12; [1094]).
He thus says first (260b19) that, since it is necessary for motion always to exist, as was proved previously, this can be understood in two ways:
first, as meaning that there exists a continuous motion;
second, as meaning that there are motions that exist one after the other, and nothing exists between them.
Now, if motion is continuous, one saves the perpetuity of motion more; moreover, it is a better thing if it be continuous rather than successive, because the former possesses more unity and perpetuity, and in nature, we ought always to take what is better, if possible. But it is possible that there be a motion that is infinitely continuous, provided it be a local motion. (This is assumed for the present, but later it will be proved.) From this, it is plain that local motion must be taken to be the first motion.
For other motions are not required for the existence of local motion. In order that a thing be moved with respect to place, it need not be either increased or altered, because a body that is in local motion does not have to be subject to generation and corruption and we know that growth and alteration affect only things that are generated and corrupted. However, none of these motions can occur unless there is that eternal motion caused by the first mover, the motion that is none other than local motion. Consequently, local motion can exist without the others but not they without it. Therefore, it is first according to the first way of being prior.
1092. Then, at “second, locomotion” (260b29), he proves that it is prior in time.
About this, he does two things.
First, he shows that, absolutely speaking, it is prior in time, because what is perpetual is, absolutely speaking, prior in time to what is not perpetual. But only local motion can be perpetual, as has been said. Therefore, absolutely speaking, it is first in time.
1093. Second, at “it is true indeed that” (260b30), he dismisses an objection through which locomotion’s temporal priority seems to be made invalid. For if we consider some one body that is newly generated, local motion seems to be the last change to affect it. For first it is generated, then it is altered and increased, and finally it undergoes local motion, when it is now perfect, as is clear in man and in many animals.
But this does not disprove the statement that, absolutely speaking, local motion is first in point of time, because, before all those motions that are found in this generated thing, a local motion had to exist in some prior mobile, which is the cause of the generation for those that are generated, as the generator is the cause of what comes to be in such a way as not to be itself generated.
That the motion that precedes generation is a local motion and that, absolutely speaking, it is the first of motions he proves thus: generation is seen to be the first of motions in things that are generated, because a thing must first be made before it is moved—and this is true in everything generated. But there must be something moved prior to what is generated and that is itself not generated; or if it is generated, then there was also something prior to it. In this way, we must either go on to infinity, which is impossible, as was proved above, or come to some first thing.
But that first thing cannot be generation, for then it would follow that all changeable things are perishable, because everything that can be generated is able to perish. Therefore, if the first mobile is something generated, it follows that it is perishable, and as a consequence, so are all the subsequent mobiles. But, if generation is not absolutely first, it is clear that none of the motions that follow it is absolutely first. And I say “motions that follow” as meaning growth, alteration, decrease, and ceasing to be, all of which follow generation in time. If, therefore, generation is not prior to local change, it follows that none of the other changes can be absolutely prior to local change. And, so, since some change must be absolutely first, it follows that local change is first.
1094. Then, at “third, that which is” (261a12), he proves that local motion is first in the order of perfection. And this he proves in two ways.
First, everything that is coming to be, while it is coming to be, is imperfect and tending to its principle—that is, to a likeness to the principle of its making—which is naturally first. From this, it is clear that what is subsequent in the order of generation is prior in the order of nature. But, in the process of generation, in all things generable, local change is found to be last, not only in one and the same thing but also in the total progress of the nature of things that can be generated. Among these, some living things are completely immobile with respect to place on account of a lack of organ, as are plants, which do not have the organs required for progressive motion, and also many types of animals. But local motion is found in the perfect animals. If, therefore, local motion is present in things to the degree that they comprehend nature—that is, in things that attain to a greater perfection of nature—it follows that local motion is, among all motions, the first with respect to the perfection of substance.
1095. Second, at “and not only for this reason” (261a20), he proves the same thing in this way. The less a motion takes away from the mobile, the more perfect is its subject, and in this regard, a motion is somehow more perfect. But it is only according to local motion that nothing in the mobile subject is taken away, for in alteration, a change with respect to a quality in the subject takes place, and in growth and decrease, a change with respect to the quantity of the subject takes place. Moreover, the change involved in generation and ceasing to be affects the very form that constitutes the substance of the subject. But local motion is only with respect to place, which contains the subject externally. It remains, therefore, that local motion is the most perfect.
1096. Then, at “above all, it is plain” (261a23), he shows that local motion is first from the side of the mobile. For it is plain that what moves itself most properly moves itself according to local motion. Since, therefore, it is something that moves itself that is the principle of other movers and mobiles and is consequently the first among all things that are moved, it follows that local motion, which is proper to it, is first among all motions. In this way, therefore, he concludes from the foregoing that change of place is the first of all motions.