Commentary Aristotle Physics
Lecture 15. Whether time exists, and whether the same “now” is in all time
Next for discussion after the subjects mentioned is time. The best plan will be to attack time by presenting extraneous reasons.
First, does it belong to the class of things that exist or to that of things that do not exist?
Second, what is its nature?
To start, then, the following considerations would make one suspect that it either does not exist at all or barely, and in an obscure way. One part of it has been and is not, while the other is going to be and is not yet. Yet time—both infinite time and any time you like to take—is made up of these. One would naturally suppose that what is made up of things that do not exist could have no share in reality.
Further, if a divisible thing is to exist, it is necessary that, when it exists, all or some of its parts must exist. But, of time, some parts have been, while others have to be, and no part of it is, though it is divisible. For what is “now” is not a part: a part is a measure of the whole, which must be made up of parts. Time, on the other hand, is not held to be made up of “nows.”
Again, does the “now” that seems to bound the past and the future always remain one and the same, or is it always different? It is hard to say.
If it is always different and different, and if none of the parts in time that are different are simultaneous (unless the one contains and the other is contained, as the shorter time is by the longer), and if the “now” that is not but formerly was must have ceased to be at some time, the “nows” too cannot be simultaneous with one another, but the prior “now” must always have ceased to be.
But the prior “now” cannot have ceased to be in itself (since it then existed); yet it cannot have ceased to be in another “now.” For we may lay it down that one “now” cannot be had next to another, any more than point to point. If, then, it did not cease to be in the next “now” but in another, it would exist simultaneously with the innumerable “nows” between the two—which is impossible.
Yes, but neither is it possible for the “now” to remain always the same. No determinate divisible thing has a single termination, whether it is continuously extended in one or in more than one dimension, but the “now” is a termination, and it is possible to cut off a determinate time.
Further, if coincidence in time (that is, being neither prior nor posterior) means to be in one and the same “now,” then, if both what is before and what is after are in this same “now,” things that happened ten thousand years ago would be simultaneous with what has happened today and nothing would be before or after anything else. This may serve as a statement of the difficulties about the attributes of time.
558. Having arrived at conclusions concerning place and the void, the Philosopher now discusses time.
First, he tells what his intention is and the order he will follow;
second, he carries out his proposal, at “to start, then” (217b32; [559]).
He first says, therefore (217b29), that our plan now calls for us to attack time, by which he signifies how difficult the subject is. And as in previous discussions, so in the case of time, one must begin by presenting extraneous reasons, that is, the opinions of others and sophistical arguments dealing with the question of whether time exists or not and, if it does, what its nature is.
Then, at “to start, then” (217b32), he begins the discussion of time:
first, by arguing against the existence of time;
second, by presenting the truth, at “we must take this” (219a1; [571]).
In regard to the first, he does two things:
first, he inquires whether time exists, arguing against it;
second, what it is, at as to what time is (218a31; [565]).
As to the first, he does two things:
first, he gives two reasons that show that time does not exist;
second, he inquires about the now, asking whether there is one now in the whole of time, or several, at “again, does the ‘now’” (218a8; [561]).
559. He says, then (217b32), that two reasons could lead us to suppose either that time does not exist at all or that it is something that can scarcely and only in an obscure way be conceived.
Here is the first reason. Anything that is composed of things that do not exist cannot have any existence or any substance. But time is composed of what does not exist, for part of time is the past, which no longer exists, and the rest is the future, which does not yet exist, and these two things comprise the whole of time considered as infinite and everlasting. Therefore, it is impossible for time to be anything.
560. He gives the second reason at “further, if a divisible thing” (218a3), which is as follows. As long as any divisible thing is existing, there must exist some part of it or a number of parts. But time does not meet these requirements, for some parts of time are already past and others are in the future, such that no divisible part of time is actually existing. And the now that is actual is not a part of time, for a part is either a measure of a whole, as two is the measure of six, or at least it is a component of the whole, as four is a part of six (although not its measure), since six is composed from it and two. Time, however, does not have nows as its parts, as will be proved below. Therefore, time is not anything.
561. Then, at “again, does the ‘now’” (218a8), he inquires whether there be the same now through the whole of time.
About this, he does three things:
first, he raises the question;
second, he objects to one side of the question, at “if it is always different” (218a11; [562]);
third, he objects to the opposite side, at “yes, but neither is it possible” (218a21; [563]).
He first says, therefore, that it is not easy to be certain whether the now that seems to distinguish the past from the future always remains identical with itself throughout the whole of time, or whether it is different.
562. Then, at “if it is always different” (218a11), he gives a reason to show that the now is not different. Two parts of time that are not the same cannot be existing together unless one contains the other, as a greater period of time contains a smaller—for instance, as a year contains the month, and the month the day (for the day and the month and the year exist together). But one now, since it is indivisible, does not contain another. If, therefore, we are to accept two nows in time, then that now that existed before the present one and no longer exists ceased to be sometime, and so two nows are never together. However, anything that ceased to be did so in some now. But it cannot be that the prior now ceased to be in that prior now, because the prior now was existing then, and nothing ceases to be while it is. Likewise, it cannot be said that the prior now ceases to be in a later one, for it is impossible to have two nows together as consecutive, so as to follow immediately one upon the other, just as the same thing is impossible in the case of two points. (This is supposed now, but will be proved in book 6.) Thus, between any two nows, there are an infinity of nows. If, therefore, that prior now ceases to be in some later now, it follows that the prior now was existing along with all the intermediate nows—which is impossible, as we have said. It is impossible, therefore, that the now be different.
563. Then, at “yes, but neither is it possible” (218a21), he gives two reasons to show that there cannot be just one now.
The first is that no finite divisible thing can have just one boundary, whether it be a divisible of one dimension, as a line, or of more than one dimension, as a plane or a solid. For the boundaries of one finite line are two points, and the boundaries of a surface are several lines, and of a body, several planes. But the now is a boundary of time. Since, therefore, it is possible to conceive of a finite time, there must be more than one now.
564. He gives a second reason at “further, if coincidence” (218a25). Those things are said to be together in time—and neither previously nor later—that are in the same now. If, therefore, it is the same now that perseveres throughout time, it follows that things that existed a thousand years ago are together with things that exist today.
Summarizing, he concludes that these are the conflicting opinions about the nows that exist in time.