Fig. 13. Four Kinds of Change in Aristotle.
Aristotle, Physics
Part 2 (Book II, Chapter 2; Book III, Chapter 1)
MCKEON: At our last meeting we started to discuss Aristotle’s analysis of motion. One thing that was apparent is that this is a different approach than that of Plato, who deals first with motion of the entire universe, then with the interrelated motions of the parts, and last with the problem of motions that an organic whole would have apart from these latter and determined by itself. What we’ve done thus far here has been, rather, to talk about nature as a principle of motion, principle in the sense of a cause of motion. In Latin, principle originally meant a beginning point; and causes are always principles, but principles are not always causes. So notice, we are not beginning with cosmic motion, though Aristotle does have a treatise on cosmic motion, called the De Caelo. We’re beginning, rather, by differentiating natural motion from other kinds of motion.
I won’t say anything more about what we’re doing since we now turn to chapter 2 of book II, and this is a chapter that I think we can go through rapidly. I’d like to get you to ask what he’s doing here. Bear in mind that what we did in chapter 1 was to raise a series of problems about what “nature” means, what “by nature” means, and what “according to nature” means; and we distinguished them in order to get nature as a principle of motion, the “natural” being that which operated according to that principle. But there would not be a coincidence in the meaning of the various terms that we have defined; rather, we’ve distinguished them. Mr. Goren?
GOREN: Yes?
MCKEON: What’s he trying to do now in chapter 2?
GOREN: He has finished this distinction. Now he goes on to ask whether there is a difference between the mathematician and the astronomer.
MCKEON: The mathematician and who?
GOREN: The physicist and the mathematician.
MCKEON: Does he get into any other science?
GOREN: He talks about optics and geometry.
MCKEON: Well, those would all be considered mathematical sciences.
GOREN: At the very end of this section, I believe, he talks about the primary type of philosophy.
MCKEON: What’s the other name for primary philosophy?
GOREN: Metaphysics.
MCKEON: Metaphysics. So, I take it that your answer is that having talked about nature, he wants to know the ways in which what we would call nature here would enter into physics, mathematics, metaphysics.
GOREN: I believe so, yes.
MCKEON: All right. Let’s take the first one: why do you have a problem here? . . . Well, go on and tell me what the difference is between the way in which the mathematician and the physicist deal with the same initial experience.
GOREN: The mathematician deals with physical lines as mathematical, whereas the physicist deals with . . .
MCKEON: How does he do that?
GOREN: He abstracts such concepts as “curved” from the material of the object which is curved.
MCKEON: All right, he abstracts from matter. Does he abstract from motion?
GOREN: Yes.
MCKEON: He abstracts from matter and motion; therefore, he deals with form separated from matter and motion. What did you decide that the physicist did?
GOREN: The physicist deals, he said, with mathematical figures as physical, that is . . .
MCKEON: Having that word physical describing the physicist’s process causes you to think that he treats matter?
GOREN: The physicist dare not ignore the matter.
MCKEON: All right. What does he deal with, then?
GOREN: His material may be in motion?
MCKEON: Yes?
STUDENT: He deals with both.
MCKEON: He deals with the matter and the form, and that’s what we said that nature was. It was more form than matter, but you couldn’t leave the matter out.
All right, we have, then, the same original experience. In other words, there’s no place that the mathematician could get his forms except from the natural objects; but his process is one of abstraction—Aristotle uses the Greek word for abstraction—, abstracting the form from the matter. If the mathematician does one thing, the physicist does another. What do you think the word in physics would be that would take the place of abstraction? . . . This is not in your reading; therefore, you can use your imagination. It’s a word that Aristotle practically invented in one sense; it existed before but not in a technical sense. It’s a word he uses constantly. Does a physicist abstract?
STUDENT: Would we say, maybe, that he makes the world intelligible?
MCKEON: What does he do if he doesn’t abstract?
STUDENT: Hypothetic.
MCKEON: Well, hypothetic is an adjective that works with a verb. How do you “hypothetic” in physics?
STUDENT: Deduction?
MCKEON: No. It’s the opposite: it’s induction. That is, Aristotle uses the word induction in a technical sense of the word. And what he’s saying here is that beginning with the same experience, the mathematician abstracts, the physicist inducts, that is, he arrives at a universal law which takes into account the matter as well as the form. One final word and then I’ll let you off the hook, Mr. Goren. What is the reference to “curved” and “snubbed,” which occurs at 194a5–6? How are the curved and the snubbed related?
GOREN: “Curved” is an abstraction such as a mathematician might use. “Snubbed” seems necessarily to imply some material.
MCKEON: Why? I mean, after all, a snubbed nose is really a curved nose.
GOREN: Well, that wasn’t quite clear to me as I read.
STUDENT: I take it that it’s a physical reference, understanding what “snubbed” means.
MCKEON: Why?
STUDENT: Well, “curved” can be any object with a curve; but for “snubbed,” in order that I give meaning to it, it has to refer to the particular physical object.
MCKEON: Again, what we’re interested in is, What kind of a term is this and why does a knowledge of snubbed differ from a knowledge of curved? Therefore, you can measure a snubbed nose; you can even nicely increase it. Yes?
STUDENT: Well, it’s of matter and form, whereas curved would only be form.
MCKEON: I know, but what does that mean? Why is it matter and form?
STUDENT: We could say that he refers to the snubness of this snubbed nose as a privation of matter.
MCKEON: You might, but that wouldn’t help us any. No, we’re talking about the basis of science. Among all the curves that are possible, the ones that you can get in a nose depend on the structure of nose, flesh, and related substances. In other words, you would have to know something about the matter and eliminate some of the curves. That is, a snubbed nose is one which would require an elementary knowledge of physiology; that enters into the picture.
Mr. Davis? He goes on to say—this is probably the only other aspect of this question he raises that we’ll touch on—that, “Since ‘nature’ has two senses, the form and the matter, we must investigate its objects . . .” [194a12–13]. What is it that we decide about what the physicist ought to know? . . . “That is, such things are neither independent of matter nor can be defined in terms of matter only” [194a13–15]. Here is where Empedocles and Democritus came along, and they voted to go along only with matter. What are we deciding now? . . . Yes?
STUDENT: We have to investigate both form and matter, and substance keeps the form of . . .
MCKEON: Well, that doesn’t help. You see, I’m trying to get out of the mere repetition of words. We now know we have to investigate form and matter, but what does that indicate about the nature of our science? He says about a half-dozen things here. I’m not aiming at any one thing; I’m aiming at something, any one of a half-dozen. Well, let me give you one thing he says. He says matter is always relative. What does that mean? I thought matter was always absolute: you weighed it and then you knew, and you could even call in the Bureau of Standards if the work was wrong. Yes?
STUDENT: If there was this relativity, is this the essence of both form and matter?
MCKEON: That may be, but this isn’t a good answer to my question.
STUDENT: Well, no. I was asking, Is that merely part of the question?
MCKEON: Oh. That would be part of the question, then.
STUDENT: But I thought that he had them both, for one reason because of the discussion about the end. In other words, sometimes matter has an end, and then it changes, which would be the form.
MCKEON: No, no. I think you’re getting involved, but you’re on the edge of the question. Matter doesn’t have an end, though the physicist does have to examine ends. This is what is known as teleology and is one of the reasons why Aristotle is criticized in modern physics. This develops a reason why I’m asking my question. What’s he driving at here? What is the significance, to get back to my question, of the statement that matter is always relative? . . . I mean, suppose, for example, I were to say that as a biologist, I will now investigate Mr. Davis at the end of the table. What would I be investigating? Or suppose someone were to ask me what matter I was investigating? Is it true that Mr. Davis’s matter is relative? What’s that mean? . . . Yes?
DAVIS: It would be equally concerned with the thing and the form; it would be concerned with the purpose which matter had in the form.
MCKEON: Well, you see, that’s what I’m afraid of. The word purpose is . . .
DAVIS: Let me use function.
MCKEON: Well, suppose it’s function. Tell me what I would do if I wanted to investigate the body. . . . Suppose I said I’m now going to investigate Mr. Davis and I pulled down a chart and I said, “Read the top line. Read the next line. Read the next line.” What would I be doing? Mr. Davis, is that investigating you? What would I be doing? . . . Well, suppose I continued to investigate you and I said now, “Drink this, eat this, drink this, and come back later and we’ll take some tests.” What would I be investigating? . . . I’d still be investigating you, wouldn’t I?
DAVIS: Yes.
MCKEON: What were the two matters I was investigating? . . . Yes?
STUDENT: The interaction of the parts in the system?
MCKEON: No. I was examining his eyesight and his digestion. What Aristotle is saying is that the matter which would be involved in those two questions would be different. What would the matter in the one case be? . . . Eyes were one thing: the eyes, the light, the size of the type, and so on. In other words, the matter is the potentiality of doing something; and if I want to know how he does something, namely, sees, I ascertain the matter which is relevant to that process. The matter which is relevant to his digestion would be made up of the parts of his digestive system and the things you stick into his digestive system. If I want to know about the process of digestion, I would examine the relative matter, and so on for all of the numerous things that I might do in the investigation of any entity. They are all as complicated as Mr. Davis is, they all have a variety of functions, but for each you would need to take a different matter. You notice, all that purpose means here is that the difference between eyes that don’t see and eyes that see, that is, dead eyes and living eyes, eyes that move, is the end; in other words, a dead eye does not see and a dead intestine does not digest. All that is involved, therefore, in the teleology is that if you want to have an animal that digests, you need a digestive system and you need food. Is this all right? Yes?
STUDENT: Well, take an eye that sees. Would the form of that eye be seeing?
MCKEON: The form of the eye is seeing. As a matter of fact, that is exactly what Aristotle says. He says that if you want to know what form is in this sense—notice, we’re taking biological examples here—it is always a function. If an ax had a function, or soul, of this kind, the soul would be cutting, and his other examples from the De Anima are treated similarly. If the eye had a soul, the soul would be seeing. Consequently, the matter that would be relevant there, the eye in this sense, would be relative to this function.
These are the two large questions that are involved in this chapter. There are some further points I would get after if we were to go into more detail. For instance, in this chapter you have the four causes making their appearance unnoticed. Also, there is one other way in which you might deal with form; that is, if you wanted to deal with the form as it is separable in itself, this is metaphysics. In the one case, you notice, we abstracted the form; but if we were dealing with the nature of forms in themselves and you then went on to their separatedness, then that is a metaphysical question.
All right. In book II we dealt with nature. There’s a lot more to book II, but it’s in book III that we get down to a consideration of motion and change. Nature was defined as the principle of motion and change. We’re now going to go into the analysis of motion itself. Let me call your attention to the opening two paragraphs of chapter 1. There are a number of things which we will have to analyze if we examine motion, and these words continue to be subject to controversy even today, namely, the nature of the continuous, the nature of the infinite, the nature of place or space, the nature of empty place or void, the nature of time. These are not our chief considerations now; therefore, let’s go on to a consideration of the analysis of motion itself.
The fifth paragraph [200b26–28] begins by telling you a variety of things about potentiality. Remember, matter was potentiality. What do we need to know in addition about potentiality? Mr. Roth?
ROTH: You have to have the different ways that potentiality is seen in matter?
MCKEON: All right. There are three ways you can distinguish them. Can you make anything out of them? What are the three relations between potentiality and actuality?
ROTH: Well, the first would be something that is a substrate. . . . I think that it could be almost nonpotentiality as a potentiality.
MCKEON: The first one is potentialities that are always actualized. What are those?
ROTH: Well, there’s one part of them that’s always being.
MCKEON: Yes?
STUDENT: Something like sight or soul, I would think.
MCKEON: No, no, those are potentialities that are actualized because sometimes you do, sometimes you don’t. Yes?
STUDENT: Could you say they’re the elements?
MCKEON: No. The elements, likewise anything that changes, would not be an instance of this. This is something in which you can only talk about the potentiality; you can’t talk about unfulfilled potentiality.
STUDENT: Would it be like a statue?
MCKEON: What?
STUDENT: He puts it back in a statue?
MCKEON: No, statues can be busted up. Yes?
STUDENT: Motion?
MCKEON: No.
STUDENT: If it is something like sight, it must be god.
MCKEON: It is god, the only god, or the unmoved mover. That is to say, god doesn’t change himself, but he performs many actions; therefore, there are no unactualized potentialities—because Aristotle uses the plural and there are more than one. The second kind, what exists as potential, is potentialities that are never actualized. What are they like?
STUDENT: Motion as motion?
MCKEON: Motion is actualized: you get somewhere. Motion is itself an actualization of a potential.
STUDENT: Well, just verbally, something like the knowable. You said that can’t be actualized.
MCKEON: No.
STUDENT: Pardon.
MCKEON: No, the knowable is a potentiality that can be actualized. You call it knowable precisely because it can be known; and when it’s known, it’s actualized. No, any infinite regress is of this sort. That is, Aristotle’s conception of infinity is to take a finite line, divide it, then keep dividing what is left each time. How long can you go on doing this?
STUDENT: Forever.
MCKEON: There’s no end to it: no matter how small the division, there is always the potentiality of a further division. Consequently, the second kind of potentiality is a potentiality which is there but is never actualized, that is, you can never get to the end. The third kind of potentiality is a potentiality which is actualized, and any kind of change or motion is of this sort. We are going to deal with this kind of potentiality, and our analysis is to proceed to that. Notice that in the discussion that follows there isn’t any such thing as motion apart from the things in motion; consequently, we’re down to the concrete instances of motion. What does this permit us to do with respect to the consideration of motion? Mr. Dean?
DEAN: Well, he gives us the properties of the things which motion always begins with.
MCKEON: All right. What are they?
DEAN: There’s substance, then quality and quantity.
MCKEON: Any attribute of substance?
DEAN: No, those would be change.
MCKEON: There are four that are enumerated. Do you know what these things—substance, quantity, quality, and place—are called?
DEAN: The categories.
MCKEON: They’re categories. How many are there?
DEAN: Ten.
MCKEON: Have you any notion of what the other six look like?
DEAN: I think they’re derived from the first.
MCKEON: They’re no more derived than the first is. The reason they’re called categories is because they’re not derivable. Here are the ten: substance, quantity, quality, relation, time, place, action, passion, posture—for this one it’s hard to know what is really best for translation—and habit. Why isn’t there motion in the others? Take relation, for example. Why isn’t there motion in relation? Or why shouldn’t there be motion in time? Why shouldn’t there be motion in posture? I was sitting down a moment ago and I got up. Yes?
STUDENT: I figure that, well, time is derived from motion.
MCKEON: No, no. Notice, time isn’t derived from motion any more than place is derived from motion. There is local motion, there is time which marks the stages of motion, but neither is derived from motion. That is, if you mean simply that you must have an experience of motion or we will not get time or space, that’s a different question. These are characteristics that have entered into any statement we make about things. What I am trying to get at is a fairly simple derivation if you stay out of the subtleties. What we have said is that there isn’t any motion except with things; and if we look at things, motion will occur only with respect to these. Why? Take, for example, when I said there was motion from my sitting posture to my standing posture, what’s wrong with that statement?
STUDENT: You can’t tell what place you’re in.
MCKEON: Oh, I know what place I’m in when I move around; the room doesn’t move. I move from one place to another, and I deliberately said I moved from sitting to standing so that the sentences are in the same form.
STUDENT: What has moved, then, is the relationship; your body is the same body but it’s moved from . . .
MCKEON: Well, but the same thing is true. I mean, if I said I moved from there to here, that’s change in place. That’s all right: it’s the same body, the body hasn’t changed. I may have gotten a little more tired, a little older, in the two minutes that are involved, but that’s . . .
STUDENT: The motion is described in terms of place, though.
MCKEON: All right. But wasn’t the motion described in terms of posture? You can see I’m standing now; I was sitting once upon a time.
STUDENT: Well, how are you going to describe it without referring to place?
MCKEON: You may have something here, but you’ve put it in the form of a question. Can you put it in the form of an argument?
STUDENT: That you couldn’t describe a changing of posture without referring to place.
MCKEON: Can anyone improve this? It’s in the neighborhood of an answer, but not a good answer. Why do you have to refer to place when talking about changes in posture? . . . Well, the only thing that happened is that parts of my body are in a different place now than before: my head went up and so did a variety of other things. Consequently, it was really a motion, a series of motions in place, and not a different kind of motion.
Why isn’t there a change in relation? First I stand to the right of the chair, and then I stand to the left of the chair; consequently, I’ve moved from the right to the left.
STUDENT: Well, nothing changes except what you’re calling it.
MCKEON: No, I really moved, but it’s local motion which I’m describing now in terms of the relative. So that what it is that Aristotle is doing is to say that there are the four fundamental differences. Remember, he said in the beginning that there are principles of change and motion; I think that will explain what the relation is. The Greek word metabolé—disguised in English as metabolism—means change. Change is divided into two kinds (see fig. 13). One kind of change is motion, and then there are the three kinds of motion. Change of substance, for reasons that I stated earlier, is not a motion. It’s a change which is instantaneous and, therefore, of a different kind. But this leads us to his conclusion. Let me put it another way: “[T]here are as many types of motion or change as there are the meanings to the word ‘is’” [201a7–8]. This would sum up what we are saying. What does that mean? . . . Yes?
STUDENT: Well, is is the word we would use with subjects and predicates, so then this thing in motion is a predicate.
MCKEON: Well, we’re back where we were. That is, why is it that I can’t say that I am on Monday? That’s one meaning of the word is; it’s why I’m here today, and I will move from Monday to Tuesday over the night. Yes?
STUDENT: The only terms you’d use to talk about anything that is are those three terms; they’re attributes of that thing.
MCKEON: No. YOU see, the categories, all ten of them that I just listed, are ways of using the word is.
STUDENT: Do you want me to put all the mistakes in a nice bundle for you? . . . First of all . . .
MCKEON: Don’t make it too hard for me. [L!] I know this fairly well.
STUDENT: I don’t think that his list at this point is really meant to be exhaustive because it does seem to me that even the posture thing is not conclusive. I mean, say that it is change of posture.
MCKEON: He didn’t bring in the list. What he did say is that this list of four is exhaustive.
STUDENT: Yeah, but his arguments later on with action and passion seem to me very—well, I think the man doth protest too much. I think of second derivatives and things like that. It seems to me there are changes of changes and . . .
MCKEON: No, no. Let me merely clean that one up. Take the difference between my doing something and my being passive to something. For instance, I begin to walk, and in the process something falls down, hits me over the head, and I have pain. The distinction between the stage when I was active and the stage when I underwent the action of something else was not a motion; it was merely a succession that could be put down temporally. The reason why it is not a motion is that it’s not a relation from things that I am; that is, it is merely a coincidence that at a given moment I stopped being active and fell down in pain because something hit me. In other words, you can use is in all of the senses; but if you are talking about a particular thing—remember, we said nature means an internal principle of motion—out of the ten senses, there are only these three that can find an internal principle of motion that would account for two successive stages of change. Notice the series of words he has here, that is, a change in quality is alteration, a change in place is local motion, the change in the size or quantity is increase and decrease, the change of substance is generation and corruption.
Let’s get on to the definition of motion that’s in the chapter. This is in one sense hard, in another sense easy. Is Mr. Milstein here? What’s the definition here of motion?
MILSTEIN: So you don’t mind my reading it back to you?
MCKEON: Well, let me put it in a shorter form which is nearer the Greek and the way in which it used to be translated before the Oxford translation came along and you got something fancy. The definition is, “Motion is the actuality”—and it’s actuality and not actualization; “fulfillment” is what it becomes in this translation. Incidentally, if you would want to know what the Greek word is, it is the very impressive word, entelekheia, an entelechy. So, “motion is the entelechy,” which is a good English word—or the actuality or the fulfillment, if you like—“of the potential”—and then there always came in—“qua potential.” Now the sentence in your book is the same sentence, but it reads, “The fulfillment of what exists potentially”—that’s the potential—“insofar as it exists potentially”—that is the “qua potential”—“is motion.” What I’m asking, Mr. Milstein, is, What does it mean to say that motion is the actuality of the potential qua potential?
MILSTEIN: Well, it’s like his example of building a building.
MCKEON: Suppose I were to ask you, What is the finished building as opposed to building, the process? How would you construct a definition of the nature of the thing?
MILSTEIN: You mean the house as opposed to the building of the house?
MCKEON: Yes. I mean, instead of motion as the actuality of the potential, the house is the actuality we want.
MILSTEIN: It would be the product of motion, of the act of motion.
MCKEON: I know, but in these terms would it be the actuality of the potential qua potential? . . . It would be the actuality of the actual qua actual, wouldn’t it? Suppose I were to say, I have a better definition of motion: it’s the actuality of the potential qua actual. How would you tell me that I was wrong? . . . You see, I’m trying to get the meaning of this sentence, and if we get these other meanings, maybe we’ll get to find out our potential qua potential. Yes? You have a suggestion?
STUDENT: Potential is qua actual when it’s actual and not already potential.
MCKEON: That isn’t true: the potential is always actual. Suppose I were talking about the process by which an oak tree grew. The oak tree grows out of an acorn into an oak. Suppose I were talking about this process and said, Now, while the oak tree is still growing, that is, it isn’t quite mature, what I’m going to focus my attention on is the potential qua actual. What would I be talking about?
STUDENT: An acorn.
MCKEON: I’d be talking about an acorn because the acorn is what is actual in the potentiality of the oak. If you want to grow yourself an oak tree, you go buy yourself an acorn or steal one or borrow one; in other words, that’s what you get, that’s an actuality you get. You stick it in the ground and do what you can. All right. We’ve done a few combinations of actualities and quas. What is the potential qua potential?
STUDENT: Well, it’s something that could be an acorn—no, you can’t use an acorn because it is qua actual—but something where the form is not complete, the potential is not actual. . . . I’m not making clear . . .
MCKEON: No, the first thing you’ve got to emphasize is that we’re talking about an actuality. There are another series of definitions we could go through, namely, what is the potentiality of the potential qua potential, and what’s the potentiality of the actual qua potential; but we’re talking about something which really is. Now what is it that we are dealing with that really is?
STUDENT: In relation to . . .
MCKEON: We’re defining motion; we’re talking about motion. What is it that is actual?
STUDENT: The movement of building.
MCKEON: The process is actual.
STUDENT: Right.
MCKEON: All right. This is a process by which the potential qua potential is brought in. Why is that? I mean, since we want to focus on the process, why is it that we focus on this point, the potential qua potential?
STUDENT: Because that, in a sense, determines the process.
MCKEON: Well, use what we just said about the potential qua actual. Why isn’t it the actuality of the potential qua actual that we’re talking about?
STUDENT: We’re not talking about that?
MCKEON: We’re not talking about the acorn. All right.
STUDENT: Oh, because it determines that this will become an oak tree rather than this becoming . . .
MCKEON: It depends on your animating the acorn.
STUDENT: Well, an acorn will become an oak tree, whereas the potential qua potential would be something like, maybe, more roots.
MCKEON: No. If you use the word potential to identify something, namely, the acorn, you use this potential to say that you’re talking about the acorn in the respect in which it’s a potentiality and not in the respect in which it’s a little round thing with a hat on it. Yeah?
STUDENT: Well, now, why talk about it that way?
MCKEON: I still want to know whether this is a good definition of motion—I nearly said why this is a good definition of motion. Let’s assume that it is. Why is this a good definition of motion?
STUDENT: It relates to the principle in terms of the nature that he’s talked about before, the internal principle of motion.
MCKEON: That’s true, but what is it emphasizing? It has three words that are important. How is it getting that internal principle of motion into our definition?
STUDENT: By talking about the potential qua potential.
MCKEON: He’s also talking about the actual. No, let me indicate what I’m trying to say. If we want to talk about motion, we can’t talk about something static; therefore, we won’t talk about a thing. Instead, we’ll be talking about a process determined by the germinating principle operating as a germinating cause. Consequently, you will get the whole sequence, which you can cut off moment to moment, of the process by which the motion has occurred from acorn to oak. The kind of motion we’re talking about here is growth. Consequently, either it could be dealt with quantitatively or, if we were dealing with different ways in which the different parts of the tree appeared and functioned, it could be dealt with qualitatively. The example of building shows the relation between nature and art. That is, it is always easier to explain what goes on in a change that is done by art because art deals with an exterior cause; therefore, you can get your causes separate. Aristotle’s assumption all the way through is that whatever nature and art do, they do in the same way; but you can make your distinctions more easily when you have an outside artist putting the form in than when you have an internal principle determining what the form would be. But in its major steps, the process would be exactly the same. It is easier to think of the process of building because you have a builder there who pours the concrete and sticks up the girders and welds them together. In the case of a natural process, the definition would still hold but without it always being possible to differentiate all the causes. You can always differentiate the material and the formal cause in nature, but the efficient and the final are sometimes hard to separate. It’s in this connection that at 201a19–22 Aristotle says explicitly that the same thing may be actual and potential; consequently, it will be acted on and will act upon others in many different ways.
Well, we’ve come to the end of our period. Let me merely sum up what he says in the rest of chapter 1, and then we can begin with chapter 2 next time. At 201a28–29 he says that motion is the actuality of the potential “when it is already fully real and it operates not as itself but as movable." Thus, if we are talking about the motion by which a statue is made, it is not the bronze about which we’re talking and out of which we made the statue that is the potentiality of the real. If we’re talking about the visible color, it can be visible if it is seen. Seeing is a motion; therefore, the matter that is seen is color. But the actual seeing, the motion, is an actualization of the potentiality; that is, color is potentially visible, and it becomes visible when it’s looked at. Then, at 201b6–7 he says that “motion is an attribute of a thing just when it is fully real in this way.” For instance, a thing is moving only when it is moving; you can’t say it’s moving either before or after. Therefore, if you’re talking about the thing, the thing is moving only while it is in motion.
Next time we’ll begin with chapter 2. We’ll go rapidly there because in chapter 2 what he does is compare his definition of motion with other definitions, including the Platonic one that you had before, and applies it to mover and moved, which raises the question which comes up in chapter 3 concerning whether the same motion is in the mover and in the movable; that is, if I push my book, is the same motion in my finger and in the book? As I say, these are, as it were, problems of clarification needed to separate them from other things, but they’re not the main issue. Therefore, I’ll try to get you through that rapidly in order to get to book V. Take a good look there at the three senses in which a thing changes. I will want to ask the same kind of question that I asked with respect to potentiality, namely, give me a example of each of these changes. From that point on, book V should move along smoothly and we will, therefore, be able to finish Aristotle next time. If we finish Aristotle next time, we can then go on to Galileo.