Commentary Aristotle Physics
Lecture 18. The meaning of “now”
Just as motion is a perpetual succession, so also is time. But every simultaneous time is self-identical, for the “now” as a subject is an identity, but it accepts different attributes. The “now” measures time, insofar as time involves the “before and after.”
The “now” in one sense is the same; in another it is not the same. It is different in motion, for this is the being of the “now,” but its substratum is an identity.
For as we said, motion goes with magnitude, and time, as we maintain, with motion.
Similarly, then, there corresponds to the point the body that is carried along, by which we are aware of the motion and of the “before and after” involved in it.
This is an identical substratum (whether a point or a stone or something else of the kind), but it has different attributes, as the sophists assume that Coriscus’ being in the Lyceum is a different thing from Coriscus’ being in the market-place.
And the body that is carried along is different, insofar as it is at one time here and at another there.
But the “now” corresponds to the body that is carried along as time corresponds to the motion. For it is by means of the body that is carried along that we become aware of the “before and after” of the motion, and if we regard these as countable, we get the “now.”
Hence, in these also, the “now” as substratum remains the same (since it is what is before and after in motion), but what is predicated of it is different, for it is insofar as the “before and after” is numerable that we get the “now.”
This is what is most knowable. For similarly, motion is known because of that which is moved, and locomotion because of that which is carried. What is carried is a real thing; the motion is not. Thus, what is called “now” in one sense is always the same; in another, it is not the same, for this is true also of what is carried.
Clearly, too, if there were no time, there would be no “now,” and vice versa. Just as the moving body and its locomotion involve each other mutually, so too do the number of the moving body and the number of its locomotion. For the number of the locomotion is time, while the “now” corresponds to the moving body and is like the unit of number.
Time, then, also is both made continuous by the “now” itself and divided at it. For here too, there is a correspondence with the locomotion and the moving body. For the motion or locomotion is made one by the thing that is moved, because it is one—not because it is one in its own nature (for there might be pauses in the motion of such a thing), but because it is one in definition, for this determines the motion as “before” and “after.”
Here, too, there is a correspondence with the point, for the point also both connects and terminates the length—it is the beginning of one and the end of another. But, when you take it in this way, using the one point as two, a pause is necessary, if the same point is to be the beginning and the end.
The “now,” on the other hand, since the body carried is moving, is always different. Hence, time is not number in the way there is “number” of the same point because it is beginning and end, but rather, as the extremities of a line form a number, and not as the parts of the line do so, for the reason given (for we can use the middle point as two, such that, on that analogy, time might stand still).
And further because, obviously, the “now” is no part of time, nor the section any part of the motion, any more than the points are parts of the line, for it is two lines that are parts of one line. Insofar, then, as the “now” is a boundary, it is not time, but an accident of it; insofar as it numbers, it is number. For boundaries belong only to that which they bound, but number (such as ten) is the number of these horses and belongs also elsewhere.
582. After explaining what time is, the Philosopher here explains the now.
First, he determines whether the now in a whole time is always the same or different, which was brought up as a problem above;
second, after settling this, he gives the reason for what is said about the now, at “clearly, too” (219b33; [588]).
As to the first, he does three things:
first, he declares that the now is somehow always the same and somehow not;
second, he explains this, at “the ‘now’ in one sense” (219b12; [584]);
third, he proves it, at for as we said, motion (219b15; [585]).
583. He says first (219b8) that, since time is the number of motion, then, just as the parts of motion are always one and another, so also the parts of time. But that which always exists throughout the whole of time is the same, namely, the now, which is always the same as to its nature, though in account it varies by being prior and subsequent. Thus, the now measures time not inasmuch as it is always the same thing, but inasmuch as, in account, it is different, and before and after.
584. Then, at “the ‘now’ in one sense” (219b12), he explains what he had just said and declares that the now is somehow always the same and somehow not. For insofar as it is always being considered as being in something different in the succession of time and of motion, in that sense, it is other and not always the same. And this is what we stated above, namely, that it is different in motion. For this is the being of the “now”; that is, it is according to this that its account is taken, namely, as considered in the succession of time and motion. But, insofar as the now is a certain being, from that viewpoint, it is always the same subject.
585. Then, at “for as we said, motion” (219b15), he proves what he has just said.
First, he proves that the now is always the same as to subject but different in account;
second, that it is the now that measures time, at “this is what is” (219b28; [587]).
He first says, therefore, that, as was said above, in respect of continuity and in respect of before and after, motion follows upon magnitude, and time upon motion. Let us imagine, therefore, after the manner of geometers, that a point in motion is making a line: then, just as there is something that remains identical in this motion, so there must be something that remains identical throughout time. If the moving point should make a line, it is by the moving point that we discern the motion and the before and after in it. For motion is perceived only because the mobile thing is in different states; according to what pertains to the previous position of the mobile, we judge something as before in motion, and according to what pertains to a subsequent position, we judge something as after in motion.
Therefore, this thing that is being moved—by which we recognize that there is motion and by which we discern a before and after in it, whether it be a point or a stone or anything else, insofar as it is a certain being, whatever it may be—is the same as to subject, but it is other in its account.
And this is the way the Sophists use the term “other” when they say that Coriscus in the forum is other than Coriscus in the theater, arguing in this way according to the fallacy of accident. To be in the forum is other than to be in the theater; but Coriscus is now in the forum and now in the theater; therefore, he is other than himself.
In like manner, it is plain that that which is being moved is other according to account—insofar as it is now here, now there—while remaining the same as to subject. Now, just as time follows upon motion, so the now follows that which is being moved. This is so because it is through the mobile that we know the before and after in motion. For when we see the mobile in some certain part of a magnitude through which it is being moved, we judge that the motion that passed through one part of the magnitude has ceased to be before and that motion through another part will follow after.
In like manner, in the counting of motion (which counting is done by time), that which distinguishes the before and after of time is the now, which is the end of the past and the beginning of the future. Thus, the now is related to time as the mobile is to motion. Therefore, also, by commuting the proportion, we get that time is to motion as the now is to the mobile.
Hence, if the mobile remains the same as to subject throughout the entire motion—though differing in account—the same will be true of the now: it too will remain the same as to subject but will be different in account. For that by which before and after are discerned in a motion is the same as to subject but differing in account, the mobile; and that according to which before and after are counted in time is the now.
586. This train of thought makes easy an understanding of eternity. For the now, insofar as it corresponds to a mobile that is continually different, distinguishes the before and after in time and, by its flow, makes time, just as a point makes a line. But, if that varying status of the mobile be removed, the substance remains always in the same state, and the now is then understood as always standing still and not as flowing nor as having a before and after. Therefore, just as the now of time is understood as the number of the mobile, so the now of eternity is understood as the number, or rather the unity, of a thing always remaining in the same state.
587. Then, at “this is what is” (219b28), he shows from what the now derives its function of measuring time. And he says it is because that which is best known in time is the now, and what is best known in any genus is the measure of everything in that genus, as is said in Metaphysics 10.
He also shows this from the relation of motion to the mobile, for motion is perceived through something being moved and local motion is perceived through observing something being moved locally, after the manner of the better known manifesting the less known.
This is so because that which is being moved is a real thing, namely, a certain thing stable in itself—a characteristic that does not belong to motion.
Hence, the mobile is more known by us than the motion, and motion is known through the mobile object. In like manner, time is made known through the now.
Thus, he reaches the conclusion principally intended: what is called the now is always the same in one way, and in another way not, because it is similar to the mobile, as was said.
588. Then, at “clearly, too” (219b33), he explains the reason for the things that are said of the now:
first, why it is said that nothing of time exists but the now;
second, why the now is said to separate and continue the parts of time, at “time, then, also” (220a3; [590]);
third, why it is said that the now is not a part of time, at “and further because” (220a18; [592]).
589. He therefore says first (219b33) that it is plain that, if there is no time, there will be no now, and if no now, no time. This is explained by the relation of motion to the mobile. For just as the change of place and that which is being moved are together, so the count of that which is being moved accompanies the count of the change of place. But time is the number of a local motion, while the now is related to what is being moved not as its number (since the now is indivisible), but as the unit of number. It follows, therefore, that time and the now are always together. Notice that time is always compared to a local motion, which is the first of all motions, for time is the number of the first motion, as was said.
590. Then, at “time, then, also is” (220a3), he explains why it is said that time is continued and divided according to the now.
First, he explains it by considering motion and the mobile;
second, by considering a line and a point, at “here, too, there is” (220a9; [591]).
He says first, therefore, that what we have already said makes clear that time is made continuous with the “now” itself—namely, by the now—and is divided by the now. This fact also follows from what is found in local motion (the number of which is time) and in the object that is being moved according to place (which corresponds to the now).
For it is clear that every motion derives its unity from the object being moved, since what is being moved remains one and the same throughout the whole course of the motion. And it is not a matter of indifference whether that which is moved in the course of one motion be any being at all, but rather it must be that same being that first began to be moved, for if it were another being that was later moved, the former motion would have failed and there would now be another motion of another mobile.
So, it is clear that it is the mobile that gives unity to the motion, which unity constitutes its continuity. But it is true that the mobile is different according to account. And it is in this way that it distinguishes the prior and the subsequent part of motion, for insofar as the mobile is considered under one account or disposition, it is recognized that whatever disposition was in the mobile previous to its present state pertained to the prior part of the motion and that whatever disposition will come after this state will pertain to the subsequent part of the motion. Thus it is that the mobile both continues the motion and distinguishes its parts. And the same holds for the now in relation to time.
591. Then, at “here, too, there is” (220a9), he explains a case of the same in the matter of line and point. And he says that the conclusion drawn about time and the now in the preceding section follows in a way from what is found in a line and a point: the point continues the line and distinguishes its parts, inasmuch as it is the beginning of one part and the end of another.
But there is a difference between the case of line and point and the case of time and the now. For both the point and the line are something stationary; hence, a person can consider the same point twice and use it as two, namely, as both a beginning and an end.
When we thus use the point as two, rest occurs, as is evident in a reflected motion, where that which was the end of the first motion is the beginning of the second and reflected motion. It is on this basis that we shall prove in book 8 that a reflected motion is not continuous, but that an intermediate pause occurs.
But the now is not stationary, for it corresponds to the mobile that is always being carried along during the motion—which also accounts for the now having to be always different in account, as was said above.
Therefore, since time is the number of motion, it does not number motion in the sense that some same time is taken as the beginning of one and the end of another, but rather it numbers motion by taking two boundaries of time, namely, two nows that are nevertheless not parts of time. The reason that this method of counting is used in numbering time, rather than the method used when a point numbers the parts of a line (where the same point is considered both a beginning and an end), is that, as was stated, in the latter method, we use the point as two things and this brings about an intermediate pause, which cannot exist in time or in motion. Now, this does not mean that the same now is not the beginning of the future and the end of the past, but that we do not perceive time by counting motion in terms of one now, but in terms of two, as was said; otherwise, in our counting of motion, the same now would be employed twice.
592. Then, at “and further because” (220a18), he explains why it is said that the now is not a part of time. And he says it is plain that the now is not a part of time, just as what distinguishes a motion is not a part of the motion—namely, some disposition in the mobile itself—just as points are not parts of a line. For two lines are the parts of a line. Now, he manifests the properties of time from the properties of motion and of line because, as was said above, motion is continuous on account of the magnitude, and time on account of the motion.
He concludes, therefore, finally, that the now, insofar as it is a certain boundary, is not time, but it is an accident of time, as a boundary does to that which is bounded; but, insofar as time or the now numbers other things, the now is the number of things other than time. The reason is that a boundary can be only of that of which it is the boundary, but a number can be applied to various things, as the number of ten horses is also that of other things. Therefore, in this way, the now is the boundary only of time, but it is the number of all mobiles that are being moved in time.