Commentary Aristotle Physics
second, he shows that, on the other hand, if each is the now, then the now must be indivisible, at “but, if this is so” (234a20; [793]).
About the first, he does two things:
First (234a5), he concludes from the foregoing that it must be the same now that is the limit of the past and of the future.
791. Second, at “for if each extremity” (234a6), he proves this statement with the following argument. If the now that is the beginning of the future is other than the now that is the end of the past, then either these two nows are consecutive and immediately follow one upon the other or one is apart from and distinct from the other. But it cannot be that they are immediately consecutive, because it will then follow that time is composed of an aggregate of nows—which cannot be, because no continuum is composed of indivisible parts, as was said above. Neither can it be that one now is apart from the other and distant from it, because there would then have to be a time between those two nows. For it is the very nature of a continuum that there is something continuous between any two given indivisibles, just as there is line between any two given points of a line.
But he proves that this is impossible in two ways.
First of all, if there were a period of time between the two nows in question, it would follow that something univocal—that is, of the same kind—would exist between the two, which is impossible, for it is not possible that there be a line between the extremities of two lines that touch or are consecutive. For that is contrary to the account of consecutive things, which were defined as things between which nothing like them occurs. And so, since future time is consecutive to past time, it is impossible that, between the end of the past and the beginning of the future, there be an intervening time.
He proves the same point in another way. Whatever is intermediate between the past and the future is called “now.” If, therefore, there is any time between the limits of the past and future, it will follow that that will also be called a now. But all time is divisible, as has been proved. Consequently, it would follow that the now is divisible.
792. Although above he has given the principles from which it could be proved that the now is indivisible, yet because he had not derived the conclusion from these principles, he now shows that the now is indivisible, at “but, if the present” (234a11).
And he does this with three arguments.
The first of these is that, if the now were divisible, it will follow that something of the past would be in the future and something of the future would be in the past. For since the now is the extremity of the past and the extremity of the future, and every extremity is in that of which it is the extremity, as a point in a line, then necessarily the entire now would be both in the past as its end and in the future as its beginning. But, if the now were divided, that division must determine the past and the future. For any division made in time distinguishes past and future, for among any parts of time taken at random, one is related to the other as past to future. It will follow, therefore, that part of the now would be past and part would be future. And so, since the now would be in the past and in the future, it will follow that something of the future would be in the past and something of the past would be in the future.
The second argument he gives at “also, the present” (234a13). If the now be divisible, it will be such not according to itself, but according to something else. For no divisible is the very division by which it is divided. But the division of time is the now. For that by which a continuum is divided is nothing but a term common to two parts. But that is what we understand by the now: a term common to the past and future. Thus, therefore, it is clear that what is divisible cannot be the now according to itself.
The third argument is given at “furthermore, there will be” (234a14). Whenever time is divided, one part is always past and the other future. If, therefore, the now is divided, necessarily part of it will be past and part future. But past and future are not the same. It will follow, therefore, that the now is not the same as itself, that is, something existing as a whole all at once (which is against the definition of the now, for when we speak of the now, we consider it as existing completely in the present); rather, there will be much diversity and even succession in the now, just as there is in time, which can be divided any number of times.
793. Therefore, having thus shown that the now is divisible (as a consequence of supposing that the now that is the extremity of the past and of the future is not identical), and having rejected this consequent, he rejects the antecedent. And that is what he says: if it is impossible for the now to be divisible, then it must be admitted that the now that is the extremity both of the past and of the future is one and the same.
Then, at “but, if this is so” (234a20), he shows that conversely, if the now of the past and of the future is the same, then it must be indivisible, for if it were divisible, all the aforementioned inconsistencies would follow.
And so, from the fact that the now cannot be admitted to be divisible (as though the now of the past were something distinct from the now of the future)—and is indeed not divisible, if the now of the present is the same as the now of the future—he concludes that it is clear that, in time, there must be something indivisible that is called the now.
794. Then, at “we will now show” (234a24), he shows that, in the now, there can be neither motion nor rest:
first, he shows it for motion;
second, for rest, at nor can anything (234a31; [795]).
He first says, therefore (234a24), that it is clear from what follows that, in the now, nothing can be in motion, for if anything were in motion in the now, two things could then be in motion, one of which is faster than the other. So, let N be the now, and let there be a faster body being moved in N through the magnitude AB. In an equal time, a slower body is moved a smaller distance. Therefore, in this instant, it traverses the smaller magnitude AG. But the faster will cover the same distance in less time than the slower. Therefore, because the slower body traversed the magnitude AG in the very now, the faster traversed the same magnitude in less than the now. Hence, the now is divided. But it was already proved that the now cannot be divided. Therefore, nothing can be moved in a now.
795. Then, at “nor can anything” (234a31), he proves the same thing for rest, giving three arguments.
The first is this. It was said in book 5 that an object at rest is one that is naturally capable of being in motion but is not in motion when it is capable of being in motion or in respect to the part by which it is capable of being in motion or in the manner in which it is apt to be in motion.
For if a thing lacks what it is not naturally capable of having (as a stone lacks sight) or lacks it when it is not naturally due to have it (as a dog lacks sight before the ninth day), or in the part in which it is not naturally capable of having it (as sight in the foot or in the hand), or in the way in which it is not apt to have it (as for a man to have sight as keen as an eagle’s), none of these reasons is sufficient for saying that a thing is deprived of sight.
Now, rest is privation of motion. Hence, nothing is at rest except what is apt to be moved, and when and as it is apt. But it has been shown that nothing is naturally capable of being moved in the very now. Therefore, it is clear that nothing is at rest in the now.
The second argument is given at “moreover, inasmuch as” (234a34). That which is being moved in an entire period of time is being moved in each part of that time in which it is apt to be moved; likewise, what is at rest in a given period of time is at rest in each period of that time in which it is apt to be at rest.