Commentary Aristotle Physics
Lecture 4
How there is motion in quantity, quality, and place, and the meaning of “immobile”
Since, then, motion can belong neither to substance nor to relation nor to agent and patient, it remains that there can be motion only in respect of quality, quantity, and place, for with each of these we have a pair of contraries.
Motion in respect of quality let us call “alteration,” a general designation that is used to include both contraries.
And by “quality,” I do not here mean a property of substance (in that sense, that which constitutes a specific distinction is a quality), but a passive quality in virtue of which a thing is said to be acted on or to be incapable of being acted on.
Motion in respect of quantity has no name that includes both contraries, but it is called increase or decrease according as one or the other is designated; that is to say, motion in the direction of complete magnitude is increase, while motion in the contrary direction is decrease.
Motion in respect of place has no name either general or particular: but we may designate it by the general name of “locomotion,” although strictly that term applies to things that change their place only when they have not the power to come to rest and to things that do not move themselves locally.
Change within the same kind from a lesser to a greater or from a greater to a lesser degree is alteration, for it is motion either from a contrary or to a contrary, whether in an unqualified or in a qualified sense.
For change to a lesser degree of a quality will be called change to the contrary of that quality, and change to a greater degree of a quality will be regarded as change from the contrary of that quality to the quality itself.
It makes no difference whether the change be qualified or unqualified, except that, in the former case, the contraries will have to be contrary to one another only in a qualified sense;
and a thing’s possessing a quality in a greater or in a lesser degree means the presence or absence in it of more or less of the opposite quality.
It is now clear, then, that there are only these three kinds of motion.
The term “immobile” we apply in the first place to that which is absolutely incapable of being moved (just as we correspondingly apply the term “invisible” to sound);
in the second place to that which is moved with difficulty after a long time or whose motion is slow at the start—in fact, what we describe as hard to move;
and in the third place to that which is naturally designed for and capable of motion but is not in motion when, where, and as it naturally would be so.
This last is the only kind of immovable thing of which I use the term “being at rest,” for rest is contrary to motion, such that rest will be privation of motion in that which is capable of motion.
The foregoing remarks are sufficient to explain the essential nature of motion and rest, the number of kinds of change, and the different varieties of motion.
678. Having shown that there is no motion in substance or in relation or in action and passion, the Philosopher now tells in which genera motion does exist.
And about this, he does three things:
first, he arrives at the intended conclusion;
second, he shows how motion is found in each of three genera, at “motion in respect of quality” (226a26; [679]);
third, he answers a difficulty, at “change within the same kind” (226b1; [682]).
He says first (226a23) that, since motion is neither in substance nor in relation nor in acting and being acted upon, as has been explained, there remain but three genera in which there is motion: quantity, quality and place, for in each of these genera, there is apt to be the contrariety that motion requires.
He has already explained both why he omits the three genera of time, position, and habit and how there is contrariety in the three genera in which motion is found.
679. Then, at “motion in respect of quality” (226a26), he explains how motion is found in the three genera:
first, in quality;
second, in quantity, at “motion in respect of quantity” (226a29; [680]);
third, in place, at “motion in respect of place” (226a32; [681]).
He first says, therefore, that motion in the genus of quality is called “alteration.” And he refers to this genus by the common name of “alteration” because, in Latin, the word alterum, meaning “other,” is customarily applied to things that differ in respect of quality.
And we are speaking of quality not in the sense in which it is found in the genus of substance, where the substantial difference is said to be predicated in regard to that which qualifies, but in the sense of a passive characteristic (contained in the third species of quality), in virtue of which something is said to receive or not receive a quality such as hot and cold, black and white, and so on. It is in respect to these that things are said to be altered, as will be shown in book 7.
680. Then, at “motion in respect of quantity” (226a29), he shows how there is motion in quantity. And he says that motion in respect to quantity does not have a name for its genus, as quality has the generic name “alteration.” Rather, it is named according to its species, which are growth and decrease. The motion from imperfect size to perfect is called “growth”; the one from perfect size to imperfect is called “decrease.”
681. Then, at “motion in respect of place” (226a32), he explains how there is motion in respect of place. He says that such motion has neither a common name for its genus nor a particular name for its species, yet he gives it the general name “bearing”—although this is not the generic name of every type of local motion. For it is properly used of things that are so moved in respect of place that it is not due to their own power that their local motion stops—in other words, things that are moved not by themselves, but by others.
The reason that the common name could be applied to motion in quality is that qualities are contrary in the very account of their species according to which they are contained under the genus of quality. But quantities are contrary not according to the very characteristics of their species, but according to perfect and diminished, as was said above; and it is according to these that the species of quantity derive their name. However, in place, the only contrariety that exists is founded on motion in respect to which two termini are most distant. Consequently, because such contrariety is based on something entirely foreign to place, no motion in this genus could possess a name based either on the genus or on the species under the genus.
682. Then, at “change within the same kind” (226b1), he clears up a point about which there could be doubt and shows to which species of motion should be reduced a change from a lesser to a greater or from a greater to a lesser degree, such as when something white becomes less white or more white. At first sight, it might seem that it should be reduced to increase and decrease. But he shows that it should be reduced to alteration, saying that any change within the same species of quality—for example, change to whiteness or to more or less whiteness—is alteration.
He proves this by the fact that alteration, which is change from one contrary to the other in respect of quality, can occur in two ways:
first, unqualifiedly, as when something changes from white to black or vice versa;
second, qualifiedly, when something changes from more white to less white, and vice versa.
And that such a change is a change from contrary to contrary he now proves. When something is changed from more white to less white, such a thing is said to be changed from one contrary to its opposite because it is approaching the true contrary, which is black. And when it is changed from less white to more white, it is as though it were changed from one contrary to its opposite, namely, from black to white. For it becomes more white by becoming further removed from black and acquiring more perfect possession of whiteness.
In order for there to be alteration, it makes no difference whether the change is unqualifiedly or qualifiedly from contrary to contrary (namely, from more to less or less to more), except that, in the former case, the termini of the alteration must be two actual contraries; but the change in regard to more and less involves the subject’s having or not having one or another of the contraries in a greater or lesser degree.
Finally, at “it is now clear” (226b8), he concludes that it is now clear that there are only these three kinds of motion.
683. Then, at the term “immobile” (226b10), he explains the various senses of “immobile,” giving three.
The term “immobile” is applied in the first place to what is absolutely incapable of being moved, like God, just as we correspondingly apply the word “invisible” to sound.
In a second sense, it is applied to what is moved with difficulty, and this in two ways: either because, after it has begun to be moved, it continues slowly and with great difficulty (as when we call a lame person immobile), or because it is difficult to get it started on account of both the labor and the time involved, as when we say that a mountain or a large rock is immobile.
In a third sense, something is called immobile when it is capable of being easily moved but it is not in motion when and where and in the manner in which it is capable. This alone is called “rest,” since rest is the contrary of motion. Here, “contrary” is used in a wide sense, in the sense that includes even privation. Hence, he concludes that rest is privation of motion in that which is capable of motion. For “contrary” and “privation” are applied only to things that are susceptible of opposites.
Finally, at “the foregoing remarks” (226b16), he summarizes and says that it is now clear from what was said what motion is and what rest is and what are the varieties of change and which of them can be called motion.