Commentary Aristotle Physics
Lecture 8
The contrariety of motions
We have further to determine what motions are contrary to each other, and to determine similarly how it is with rest.
And we have first to decide whether contrary motions are motions respectively from and to the same thing, such as a motion from health and a motion to health (where the opposition, it would seem, is of the same kind as that between generation and ceasing to be);
or motions respectively from contraries, such as a motion from health and a motion from disease;
or motions respectively to contraries, such as a motion to health and a motion to disease;
or motions respectively from a contrary and to the opposite contrary, such as a motion from health and a motion to disease;
or motions respectively from a contrary to the opposite contrary and from the latter to the former, such as a motion from health to disease and a motion from disease to health.
For motions must be contrary to one another in one or more of these ways, as there is no other way in which they can be opposed.
Now, motions respectively from a contrary and to the opposite contrary—for instance, a motion from health and a motion to disease—are not contrary motions, since they are one and the same. (Yet their essence is not the same, just as changing from health is different from changing to disease.)
Nor are motions respectively from a contrary and from the opposite contrary, contrary motions, for a motion can go at the same time to a contrary or to an intermediate (of this, however, we shall speak later).
But changing to a contrary rather than changing from a contrary would seem to be the cause of the contrariety of motions, the latter being the loss of contrariness, and the former the gain.
Moreover, each several motion is called rather from the goal than from the starting point of change—for instance, motion to health we call convalescence, and motion to disease we call sickening.
Thus, we are left with motions respectively to contrary goals and motions respectively to contraries from the opposite contraries.
Now, it would seem that motions to contraries are at the same time motions from contraries (though their essence may not be the same—“to health” is distinct, I mean, from “from disease,” and “from health” from “to disease”).
Since, then, change differs from motion (motion being change from a particular subject to a particular subject), it follows that contrary motions are motions respectively from a contrary to the opposite contrary and from the latter to the former—for instance, a motion from health to disease and a motion from disease to health.
Moreover, the consideration of particular examples will also show what kinds of processes are generally recognized as contrary.
Thus, falling ill is regarded as contrary to recovering one’s health, and being taught as contrary to being led into error not by oneself, these processes having contrary goals (it being possible to acquire error, like knowledge, either by one’s own agency or by that of another).
Similarly, we have upward locomotion and downward locomotion, which are contrary lengthwise, locomotion to the right and locomotion to the left, which are contrary breadthwise, and forward locomotion and backward locomotion, which too are contraries.
On the other hand, a process simply to a contrary—for instance, that denoted by the expression “becoming white”—where no starting point is specified, is a change, but not a motion.
And, in all cases of a thing that has no contrary, we have as contraries change from and change to the same thing. Thus, generation is contrary to ceasing to be, and losing to gaining. But these are changes and not motions.
And, wherever a pair of contraries admits of an intermediate, motions to that intermediate must be held to be in a sense motions to one or other of the contraries, since the intermediate serves as a contrary for the purposes of the motion, in whichever direction the change may be.
For instance, grey in a motion from grey to white takes the place of black as starting point, and in a motion from white to grey, it takes the place of black as goal, and in a motion from black to grey it takes the place of white as goal.
For the middle is opposed in a sense to either of the extremes, as has been said above.
Thus, we see that two motions are contrary to each other only when one is a motion from a contrary to the opposite contrary and the other is a motion from the latter to the former.
715. After discussing unity and diversity of motions, the Philosopher now discusses contrariety of motions, which is a kind of diversity, as is evident from Metaphysics 10.
His treatment is divided into two parts: in the first, he shows how to understand contrariety in motion and in rest; in the second, he raises some questions about such contrariety, at “again, a further difficulty” (230a18; [737]).
About the first, he does two things: first, he settles the problem of contrariety of motion;
second, about contrariety of states of rest, at “but, since a motion appears” (229b23; [727]).
About the first, he does three things: first, he distinguishes diverse ways according to which contrariety of motion might be taken; second, he rejects some of these ways, at “now, motions respectively” (229a16; [717]); third, he assigns the true way in which motions and changes are contrary, at “since, then, change differs” (229a30; [722]).
716. He says first (229a7) that it is now time to decide how one motion is contrary to another, as well as how it is with rest, that is, how rest is contrary to motion and rest to rest.
But, in this treatment, we must first distinguish the ways according to which the idea of contrariety in motions can be taken universally.
And he distinguishes five ways.
The first of the five is that one idea of contrariety in motions is based on one motion approaching a definite terminus and another departing from the same terminus: whether contrary motions are motions respectively from and to the same thing, such as a motion from health and a motion to health. According to this, generation and corruption seem to be contrary, because generation is a motion to being, and ceasing to be from being.
The second way is that the idea of contrariety of motions is based on contrariety of the termini from which the motions begin: or motions respectively from contraries, such as a motion from health and a motion from disease.
The third way is that contrariety of motions is based on the contrariety of the goals at which they are terminated: or motions respectively to contraries, such as a motion to health and a motion to disease.
The fourth way is to take contrariety of motions according to the contrariety existing between the start of one and the goal of the other: or motions respectively from a contrary and to the opposite contrary, such as a motion from health and a motion to disease.
The fifth way is based upon contrariety on the part of both termini of each motion: or motions respectively from a contrary to the opposite contrary and from the latter to the former, such as a motion from health to disease and a motion from disease to health.
Now, contrariety among motions is necessarily based either on one of these five ways or on more than one, for there is no other possible way of one motion being contrary to another.
717. Then, at “now, motions respectively” (229a16), he rejects two of these five.
He first rejects the fourth way, which based contrariety on the opposition between the start of one and the goal of the other.
Second, he rejects the second, which based contrariety on the opposition between the start of one and the start of the other, at “nor are motions respectively” (229a20; [718]).
Third, he concludes how two of the remaining ways are related, at “thus, we are left with” (229a27; [721]).
He says first (229a16), therefore, that a motion that begins at one contrary cannot be called contrary to a motion that tends to the opposite contrary, such as to say that a change from health is contrary to a change to sickness. For nothing is contrary to itself; but a motion from health is one and the same as a motion to sickness, although their essence is not the same, that is, they differ in definition, inasmuch as a change from health is not the same idea as a change to sickness: one gives the idea of the starting point and the other the goal of the same motion. Consequently, contrariety of motion must not be taken from the viewpoint of the contrariety existing between the start of one and the end of the other.
718. Then, at “nor are motions respectively” (229a20), he shows that contrariety must not be taken from the contrariety existing between the two starting points of two motions.
This is for three reasons.
The first is the following. Two motions that tend to the same goal are not contrary; but two motions that start from contraries can tend to one and the same goal, for a motion can go at the same time—that is, equally—either to a contrary or to what is intermediate between the contraries, as will be said later. Thus, two motions that start from contraries could terminate at the same intermediate. Consequently, motions are not contrary just because they start at terms that are contrary.
719. He gives the second reason at “but changing to a contrary” (229a22), which is this. The idea of contrariety in motion must be based on that which more evidently makes the motion contrary, but contrariety between goals at which motions end seems to be a greater cause of contrariety in motions than is contrariety between termini from which motions start.
For when I say that motions begin at contrary terms, I am stressing the removal of contrariety, but when I say that motions are approaching contrary goals, I am stressing the receiving of contrariety. Therefore, contrariety of motions is not based solely on the termini from which they start.
720. He gives the third reason at “moreover, each several motion” (229a25), and it is this. Things receive contrariety from that from which they take their name and species, for contrariety is a difference based on form, as is clear in Metaphysics 10. But every motion is called, that is, gets its name, and species from the goal more than from the starting point, as healing is a motion to health and getting sick is a motion to sickness. This point was mentioned before. Therefore, contrariety of motions is taken rather from the goal than from the terminus at which they start. Thus, our conclusion is the same as before.
721. Then, at “thus, we are left with” (229a27), he concludes that, having rejected the two ways that were based on the contrariety of termini, there remain two other ways, the third and the fifth.
Of these, one is based solely on the contrariety of goals, which he touches on at “to contrary goals”; and the other on the contrariety of both sets of termini, which he touches on at “to contraries from the opposite contraries.”
The first way was not based on any contrariety of termini, but on approach and departure from the same terminus. He further concludes that perhaps these two remaining ways are really the same in subject, because motions that tend to contrary goals also start at contraries; but perhaps they are not the same in account, because of the various relationships that exist between motions and their termini, as was said above. For example, a motion to health is really the same as a motion from sickness, but they differ in account. The same is true for a motion from health and a motion to sickness.
722. Then, at “since, then, change differs” (229a30), he explains how to take contrariety in motion: first, when the motion tends toward a contrary; second, when it tends toward the intermediate, at “and, wherever a pair of contraries” (229b14; [726]).
About the first, he does two things: first, he explains what makes for contrariety in motions; second, in changes, at “on the other hand” (229b10; [724]).
About the first, he does two things: first, he explains his proposition with a syllogism; second, by induction, at “moreover, the consideration of” (229b2; [723]).
As to the first, he gives this reason (229a30). The contrariety of things is based on their specific nature and definition. But the specific definition of motion is that it is a change that takes place from a definite affirmed subject to a definite affirmed subject and that two termini are involved. (On this point, motion differs from change, which does not always require two affirmed termini.) Therefore, we are left with the fact that, for contrariety of motion, there must be contrariety on the side of both termini. In other words, a motion that goes from contrary to contrary is, strictly speaking, contrary to one that is from contrary to contrary; for example, one that is from health to sickness is contrary to one from sickness to health.
723. Then, at “moreover, the consideration of” (229b2), he proves the same by induction.
He does so first of all in bodily alterations, for to fall ill is contrary to getting well. In these two examples, the first is from health to sickness and the other from sickness to health. This is also evident in changes that occur in the soul, for to learn is contrary to being led into error, not by oneself but by another. These two motions are also from contraries to contraries, because learning is a motion from ignorance to knowledge, and being deceived is from knowledge to ignorance.
He says not by oneself because, just as it is possible in the case of knowledge for a person to acquire it by himself (and this is called “discovery”) or with someone’s help (and this is called “learning”), so also it can happen that a person is led into error sometimes by himself and sometimes by another. It is the latter that is properly opposed to learning.
Continuing, we take an example from local motion. For an upward motion is contrary to a downward (and these are contrary in respect of length); a motion to the right is contrary to one to the left (and these are contrary in respect of breadth); and a motion forward is contrary to one backward (and these are contrary in respect of depth).
But notice that Aristotle is here speaking of differences of position as they apply to man: up and down are measured in respect to man’s length; left and right in respect to his breadth; fore and after in respect to his thickness, which is called height or depth.
Moreover, it should be noted that, even in natural motions, there is a contrariety based on up and down; but, in regard to right and left or forward and backward, the contrariety is not according to nature, but according to motions that originate from the soul, which has motions toward these contrary directions.
724. Then, at “on the other hand” (229b10), he shows how there is contrariety in changes.
First, he explains how to take contrariety of change in things in which contrariety is found;
second, how to take it in things in which there is no contrariety, at “and, in all cases” (229b11; [725]).
He says first (229b10) that, if contrariety is taken merely from the goal, such that what tends to a contrary is said to be contrary, such a process does not make for contrariety of motion, but of change, which is generation and ceasing to be, as becoming white and becoming black are contrary. Now, the contrariety of these instances of generation is not based on the contrariety of the starting point, because the starting point in generation is not something affirmed, but something negated, for the white comes to be from the non-white, not from something affirmed. For a change from subject to subject is not change, but motion.
725. Then, when he says “and, in all cases” (229b11), he shows that in things in which there is no contrariety—for example, in substances and the like—contrariety of change is based on approach and departure from the same terminus. And this is what he says: in those things in which there is no contrariety, contrariety of change is taken from recession to the thing and accession to the same; for instance, accession to the form of fire, which pertains to the generation of fire, and receding from the same form, which pertains to its ceasing to be, are contraries. Hence, generation is contrary to ceasing to be and any loss is contrary to any gain. But these are changes, not motions.
It is therefore evident that, of the five ways listed above: the second and fourth are of no use; one of the remaining is suitable for knowing contrariety of motions; and the other two are suitable for contrariety of changes.
726. Then, at “and, wherever a pair of contraries” (229b14), he decides about contrariety of motion from the viewpoint of the intermediate between contraries. And he says that, wherever a pair of contraries admits of an intermediate, motions to that intermediate must be held to be somehow motions to one or other of the contraries, for the intermediate serves as a contrary for the purposes of motion, no matter in which direction the change may be. For example, grey in a motion from grey to white takes the place of black as starting point, but in a motion from white to grey, it takes the place of black as goal. For the middle is, in a sense, opposed to either of the extremes, as has been said above; in comparison to white it is black, and in comparison to black it is white, as was said above.
Finally, he concludes what he mainly intended: a motion is contrary to a motion when they are from contrary extremes.