Commentary Aristotle Physics
These two are the same as the two he mentioned above, when he said if the same thing is found in things that are other, or if differing things are found in differing things. For it is clear that there is a same reason of identity and diversity in species and in definition.
949. Then, at and further, where alteration (249a29), he discusses the comparison of alterations.
About this, he does two things:
first, he shows that one alteration is as fast as another;
second, he investigates from what aspect equality of quickness in alteration is considered, at but what alteration (249b2; [950]).
He first asks, therefore, about alteration, how one alteration is as fast as another. And he proves that two alterations are equally fast. For being healed is to be altered. But one can be healed swiftly and another slowly, and likewise, some come to be healed at the same time. Therefore, one alteration is as swift as another, for what is moved in an equal time is said to be moved with equal speed.
950. Then, at but what alteration (249b2), because equality of speed in local motion requires equality not only of time but also of magnitude traversed, and assuming that, in alteration, equality of time is required for equality of speed, he asks what else is required: but what alteration? What is it that must be reached in equal time in order that an alteration be called equally swift?
And the reason for this question is that, in quality, with which alteration is concerned, the equal is not found such as to enable us to say that, when an equal quantity is reached in equal time there is an equally fast alteration, as indeed happens in local motion as well as in growth and decrease. But, just as equality is found in quantity, so likeness is found in quality.
To this question he responds at “however, let us say” (249b4). And first he answers the question, saying that alterations should be called equally swift if, in an equal time, it is the same change that has been changed—that is, altered.
951. Second, at “are we, then, to find” (249b5), he raises a question about this answer. Since it has been said that there is an equally swift alteration if it is the same thing that has been altered in an equal time, and since, in that which has been altered, there are two things to consider—namely, the quality with respect to which alteration occurred and the subject in which the quality exists—this question arises. Should a comparison of this sort be regarded from the viewpoint of the identity of the quality or from that of the identity of the subject in which the quality exists?
952. Then, at “in the case that we have” (249b5), he answers one part of the question and says that, with respect to the quality received in alteration, two types of identity must be considered in order that alterations be equally swift.
First, the same specific quality must be involved, for example, the same health of the eye or of something similar;
second, the quality that is taken must be present in the same way, and neither more nor less.
But, if the passions—that is, the passible qualities in question—differ specifically, such as if one alteration involves becoming white and another healthy, then in these two cases nothing is the same; they are neither equal nor alike. Hence, a diversity of these qualities causes a diversity in species of alteration, such that the alterations are not one, just as it was said above that a straight motion and a circular one are not one local motion. Consequently, whenever you wish to compare either local motions or alterations, you have to consider the species of alterations or of local motion to see whether they are the same or many. And this may be considered from the things in which motions occur, for if the things that are in motion—that is, in which motion occurs per se, and not per accidens—differ specifically, then the motions differ specifically; if they differ generically, so do the motions differ generically; if they differ numerically, then also the motions differ numerically, as was pointed out in book 5.
953. Third, at “but there still remains” (249b14), having determined one part of the question he raised, he now attacks the other: in order that alterations be adjudged similar or equally swift, should regard be paid only to the quality to see if it is the same, or also to the subject that is altered? That is, if a certain portion of this body becomes white in a certain time and an equal part of another becomes white in the same or in equal time, should the alterations be judged equally swift?
And he answers that attention must be paid to both the quality involved and the subject, but in different ways. For from the viewpoint of the quality, we judge an alteration to be the same or different according to whether the quality is the same or not; but we judge an alteration to be equal or unequal if the part of the subject altered is equal or unequal. For if a large part of this body becomes white and a small part of another becomes white, the alterations will be specifically the same, but they will not be equal.
954. Then, at and now we must consider (249b19), he shows how comparison should be made with respect to generation and ceasing to be:
first, according to his own opinion;
second, according to the opinion of Plato, at if we adopt the theory (249b23; [955]).
He says first (249b19) that, in generation and ceasing to be, in order that a generation be called equally swift, we must consider whether, in an equal time, the same thing is generated and is something indivisible as to species—for example, if a man is begotten in equal time in both generations, they are equally swift. But generations are not equally swift just because an animal is generated in equal time, for some animals, on account of their perfection, require more time for being generated. But generation is said to be swifter if something else is generated in an equal time—for instance, if in the same time in one part of which a dog is generated, and in another part of which a horse is generated, the horse is generated more quickly.
And, since he had said that, in alteration, two things must be considered from the viewpoint of the quality involved—namely, whether it is the same health and whether it exists in the same way and not more or less—while here he says that, in generation, only one thing has to be considered, namely, whether it is the same that is being generated, he now gives the reason for this difference, saying, because we do not have two things in which there is an otherness called unlikeness.
It is as if he said that the reason that the only thing to be considered in generation is whether it is the same thing that is being generated is that, in generation, we do not have something that could vary with regard to two things, according to which a difference could be discerned in the way that unlikeness occurs in alteration through the fact that one and the same quality can vary according to more and less. For a substance, which is the proper terminus of generation, is not capable of more and less.
955. Then, at “if we adopt the theory” (249b23), he discusses the comparison of generations according to the opinion of Plato, who supposed that number is the substance of a thing. For he thought that the one that is the principle of number is the substance of a thing. Now, what is one is entirely of one nature and species. Therefore, if number, which is nothing more than an aggregate of units, is, according to Plato, the substance of things, it follows that a number will be called larger or smaller according to the species of quantity, but as to substance, it will be of like species. And hence it is that Plato declared that one is the species, but that the contraries through which things differ are the large and the small, which are considered from the side of the matter. Accordingly, it will follow that, just as one and the same health has two aspects, inasmuch as it receives more and less, so also substance, which is number (since it is of the same species on account of unity), will have two aspects according as the number is larger or smaller. But, in substance, no general word exists to signify both, that is, the diversity which arises from the largeness and smallness of number. In qualities, when more of one is in a subject or when it is in any way outstanding, the quality is said to be more—for example, “more white” or “more healthy.” And, in quantity, excellence is described as greater, as a greater body or a greater surface. But, in this sense, there is no common word to signify excellence in substance—which is due to the largeness of number, according to the Platonists.