Commentary Aristotle Physics
Lecture 5
The “now” of time and the solution of various difficulties
The present also is necessarily indivisible—“the present” not in the sense in which the word is applied to one thing in virtue of another, but in its proper and primary sense, in which sense it is inherent in all time.
For the present is something that is an extremity of that which was done (no part of the future being on this side of it) and also of the future (no part of the past being on the other side of it): it is a limit of both, as we have said. And, if it is once shown that it is essentially of this character and one and the same, it will at once be evident also that it is indivisible.
Now the present that is the extremity of both times must be one and the same.
For if each extremity were different, the one could not be consecutive to the other, because nothing continuous can be composed of things having no parts.
And, if the one is apart from the other, there will be time between them, because everything continuous is such that there is something univocal between its limits and described by the same name as itself.
But, if the intermediate thing is time, it will be divisible, for all time has been shown to be divisible. Thus, on this assumption, the present is divisible.
But, if the present is divisible, there will be part of the past in the future and part of the future in the past, for past time will be marked off from future time at the actual point of division.
Also, the present will be a present not in the proper sense, but in virtue of something else, for the division that yields it will not be a division proper.
Furthermore, there will be a part of the present that is past and a part that is future, and it will not always be the same part that is past or future.
In fact, one and the same present will not be simultaneous, for the time may be divided at many points. If, therefore, the present cannot possibly have these characteristics, it follows that it must be the same present that belongs to each of the two times.
But, if this is so, it is evident that the present is also indivisible, for if it is divisible, it will be involved in the same implications as before. From what has been said, then, it is clear that time contains something indivisible, and this is what we call a present.
We will now show that nothing can be in motion in a present. For if this is possible, there can be both quicker and slower motion in the present. Suppose that, in the present N, the quicker has traversed the distance AB. That being so, the slower will in the same present traverse a distance less than AB, say AG.
But, since the slower will have occupied the whole present in traversing AG, the quicker will occupy less than this in traversing it.
Thus, we shall have a division of the present, even though we found it to be indivisible. It is impossible, therefore, for anything to be in motion in a present.
Nor can anything be at rest in a present, for as we were saying, only that can be at rest that is naturally designed to be in motion but is not in motion when, where, or as it would naturally be so. Thus, since nothing is naturally designed to be in motion in a present, it is clear that nothing can be at rest in a present either.
Moreover, inasmuch as it is the same present that belongs to both the times, since it is possible for a thing to be in motion throughout one time and to be at rest throughout the other, and since that which is in motion or at rest for the whole of a time will be in motion or at rest, as the case may be, in any part of it in which it is naturally apt to be in motion or at rest— this being so, the assumption that there can be motion or rest in a present implies that the same thing can at the same time be at rest and in motion, for both the times have the same extremity, namely, the present.
Again, when we say that a thing is at rest, we imply that its condition in whole and in part is, at the time of speaking, uniform with what it was previously; but the present contains no “previously”; consequently, there can be no rest in it.
It follows, then, that the motion of that which is in motion and the rest of that which is at rest must occupy time.
Further, what is being changed must be divisible. For since every change is from something to something, and a thing is no longer changing when it is at the goal of its change, and when both it itself and all its parts are at the starting point of its change, it is not changing (for that which is in whole and in part in an unvarying condition is not in a state of change), it follows, therefore, that part of that which is being changed must be at the starting point, and part at the goal, for as a whole, it cannot be in both or in neither.
(Here, by “goal of change,” I mean that into which it is first changed during the process of change: for instance, in a process of change from white, the goal in question will be grey, not black, for it is not necessary that what is changing should be at either of the extremes.)
It is evident, therefore, that everything that changes must be divisible.
787. After showing that no continuum is composed of indivisibles and that no continuum is indivisible, thus making it clear that motion is divisible, the Philosopher now determines about the division of motion.
First, he states certain facts necessary for the division of motion;
second, he treats of the division of motion, at “now, motion is divisible” (234b21; [806]).
About the first, he does two things:
first, he shows that, in an indivisible point of time, there is neither motion nor rest;
second, that an indivisible cannot be moved, at “further, what is being changed” (234b10; [796]).
About the first, he does two things:
first, he shows that the indivisible point of time is the now;
second, that, nothing is being moved or is at “rest in the now, at we will now show” (234a24; [794]).
About the first, he does three things:
first, he states his intention;
second, he states facts from which his proposition can be reached, at “for the present” (233b35; [789]);
third, he shows what follows from his proposition, at “now the present” (234a5; [790]).
788. About the first (233b33), we must take into account that something is called “now” in relation to something else and not in relation to itself; for example, we say that what is being done in the course of a whole day is being done now, yet the whole day is not said to be present according to its entirety, but according to some part of itself.
For it is evident that part of a whole day has passed and part is still to come, and neither of them is now. Thus, it is evident that the entire present day is not a now primarily and per se, but only through something belonging to it—and what is true of the day is true of an hour or any other period of time.
He therefore says that what is now primarily and per se and not according to something else is necessarily indivisible and present in every time.
789. Then, at “for the present” (233b35), he proves his proposition. For it is evident that it is possible in regard to any finite continuum to take an extremity outside of which there is existing nothing of that of which it is the extremity, just as nothing of a line is outside the point that terminates the line. But past time is a continuum that is terminated at the present. Therefore, it is possible to take something as the extremity of that which was done—that is, the past—such that there is nothing of the past beyond it, and nothing of the future previous to it. In like manner, it is possible to take an extremity of the future beyond which there is nothing of the past. Now, that extremity will be the limit of both, of the past and of the future; for since the totality of time is a continuum, the past and the future must be joined at one term. And, if the now fits the description just given, it is clear that it is indivisible.
790. Then he shows what follows from these premises, at “now the present” (234a5).
About this, he does two things:
first, he shows that, on the supposition that the now is indivisible, the limit of the past and the limit of the future must be one and the same now;