Commentary Aristotle Physics
Therefore, if a subject should be passing from one change to another—for example, from getting sick to getting white—while it is at the same time changing from health to sickness, it will be passing from one change into another change. For while the subject is still partially in the terminus from which, it is being moved to the terminus to which, just as, while it still has some health, it is being moved to sickness.
Now, if the very motion from health to sickness is the terminus from which of some motion, then, while that change (from health to sickness) is still going on, the subject is at the same time passing from this change into another change, which succeeds in the subject to the first change. But it is evident that, when the first change shall have ended—that is, when someone has now already changed from health to sickness—some other change could succeed it. And this is not strange, for after the first change is over, the subject might remain at rest or it might be affected by another change. Therefore, if there is a passing from the first to the second change, it will follow that the motion goes from the first change to an indeterminate goal. And this is against the true account of per se motion, because every motion is from a definite terminus to a determinate goal, for a body does not change per se from white to just anything, but to black or to something intermediate. It is evident, therefore, that two changes cannot be the per se termini of a change.
671. He proves this same point again with another argument: if the passing from a previous changing to a subsequent change were motion per se, then it would not be necessary that the passing be always to a contingent change—that is, one that could co-exist with the previous change, as becoming white can co-exist with becoming sick, but getting well cannot co-exist with getting sick because these are contrary changes.
But it is possible that, just as becoming white can follow becoming sick in the same subject, so also could becoming well. And this is what he says: that the passing from one change to another will not always be to a contingent change, since it is sometimes to a non-contingent, and that non-contingent change proceeds from something definite to some other definite thing; that is, it is between two other termini. Hence, that non-contingent change into which something passes from the change called getting sick will be getting well, which is the opposite of getting sick.
Now, that this is strange is evident from what we have said above: while the first change is still going on, it is being changed to the second change, and thus, while something is being moved to sickness, it will be changing to another change called getting well. But the goal of getting well is health (for it is from something to something, as was said).
Hence, it remains that, while something is being moved to sickness, it is at the same time being moved to health, which means it is being moved toward two contraries at the same time and intends them at the same time—which is impossible. Consequently, it is clear that no change from one change to another is per se.
However, that such a thing can take place per accidens, as he had said before, he makes clear when he says that this can happen per accidens, as when a subject is now affected by one change and later by another—for example, if someone is changed per accidens from remembering to forgetting or to any other change—because the subject of the change is sometimes changed to knowledge and sometimes to something else, such as to health.
672. At in the second place (225b33), he presents two conditional propositions before giving the second of the six reasons he promised. The first of these is that, if there is change of change and generation of generation, it would be necessary in either case to go on to infinity, because, for the same reason, the second generation will have another generation, and so on to infinity.
The second conditional is that, if generations and changes are so arranged that there is change of change and generation of generation, then, if there is a last change or generation, there necessarily had to be a first.
This second conditional he now proves. Let fire be the thing that is unqualifiedly generated; if, then, there is a generation of generation, it is necessary to say that that unqualified generation was itself generated and that its coming to be came to be.
When, however, that generation was being generated, the fire was not existing (for it is being assumed that the fire is being unqualifiedly generated), because a thing does not exist while it is coming to be, but it exists for the first time after it has come to be.
Therefore, as long as the generation of fire was in the state of coming to be, the fire had not yet come to be; therefore, it was not yet existing. And, again, the very generation of its generation was itself coming to be, for the same reason.
Consequently, just as, when the generation of the fire was coming to be, the fire did not exist, so also, as long as the generation of the generation was taking place, the generation of the fire was not existing.
From this it is clear that generation of fire cannot exist till that generation is completed, and for the same reason, the previous generation of the generation of the fire, and so on to the first. Consequently, if there was no first generation, there will be no last—that is, no generation of the fire. But, if an infinite process be posited in cases of generation, there will be no first change and no first generation, because there is no first in the realm of the infinite. Hence, it follows that there is no following stage to be had among generations and among changes. But, if there is no generation or change, nothing comes to be and nothing changes. Consequently, if there were generation of generation or change of change, nothing would ever come to be or change.
Note, however, that this argument does not exclude the possibility of one change following another to infinity per accidens, which has to be admitted according to the opinion of Aristotle, who posited eternal motion. But the argument intends to show that there is no per se change to infinity, for in that case, a present change would depend on an infinitude of preceding changes and would never end.
673. He gives the third reason at “third, if a thing” (226a6), and it is this. One and the same motion has as its contraries both motion and rest; for example, both descending and rest in the lower place are contrary to ascending. In the same way are generation and ceasing to be contrary. But contraries are apt to affect the same thing. Therefore, whatever comes to be can cease to be.
But, if there is coming to be of coming to be, then coming to be must come to be. Therefore, coming to be ceases to be. But what ceases to be must be, for just as only what is not comes to be, so only what is ceases to be. Therefore, it is necessary that when what comes to be comes to be—that is, when something comes to be and the coming to be exists—then the very coming to be ceases to be, not indeed as soon as the coming to be is finished or some time after it is finished, but during the coming to be—which seems absurd.
But it should be observed that coming to be is as a terminus of what comes to be as a substance does, because coming to be is a change tending to substance. But the subject of coming to be is not what comes to be, but its matter. Hence, Aristotle is not departing from his proposition that there is no change of change as of a terminus.
674. He gives the fourth reason at “fourth, there must be” (226a10). In every coming to be, there must be matter from which that which comes to be is generated, just as every change requires some matter or subject. For example, in alteration, the subject is the body, if you are dealing with bodily qualities, or the soul, if you are dealing with qualities of soul. If, therefore, generation comes to be, there must be some matter of the generation itself (namely, which passes into the form), as the matter of generated fire passed into the form fire. However, such matter is not discoverable.
In the same vein, he makes use of another middle term: in every coming to be or change, there must be involved a goal toward which something is moved. And this goal must be something definite and capable of being pointed out. But neither change nor coming to be is such a goal. Therefore, it is not possible that there be either change of change or coming to be of coming to be.
675. He gives the fifth reason at “but in what sense” (226a14), which is this: genus is to genus as species is to species. If, therefore, there is coming to be of coming to be, then the coming to be of teaching is itself teaching. But this is evidently false, since teaching is the generation of science and not of teaching. Therefore, neither can there be a coming to be of coming to be.
676. He gives the sixth reason at “finally, since there are” (226a16), and it is this: if there is change of change, whether as of a subject or as of a terminus, then, since there are three species of motion, as was said above (motion to where and quantity and quality), it will follow that one of these species could be the subject and terminus of some other species, or even of its own species. Therefore, it will follow that local motion can be altered or even be moved locally. Such a thing is more plainly absurd when you get down to cases than when you speak in general. Therefore, it cannot be admitted that there is change of change or coming to be of coming to be.
677. Then, at “to sum up, then” (226a19), he shows in what sense there can be change of change. He says that, since there are three ways in which something can be moved, as was said above—namely, in respect to an accident or in respect to a part or per se—it is only per accidens that there could be change of change, that is, only inasmuch as the subject of the change changes. For example, if someone, while he is becoming healthy, would run or learn, then the healing process would be running or learning per accidens, just as a musician builds per accidens. But it is not our intention to treat of per accidens motion, for we have already decided to pass it by.