by Aristotle
We must take this as our starting-point and try to discover—since we wish to know what time is—what exactly it has to do with movement.
Now we perceive movement and time together; for even when it is dark and we are not being affected through the body, if any movement takes place in the mind [5] we at once suppose that some time has indeed elapsed; and not only that but also, when some time is thought to have passed, some movement also along with it seems to have taken place. Hence time is either movement or something that belongs to movement. Since then it is not movement, it must be the other.
But what is moved is moved from something to something, and all magnitude [10] is continuous. Therefore the movement goes with the magnitude. Because the magnitude is continuous, the movement too is continuous, and if the movement, then the time; for the time that has passed is always thought to be as great as the movement.
The distinction of before and after holds primarily, then, in place; and there in [15] virtue of relative position. Since then before and after hold in magnitude, they must hold also in movement, these corresponding to those. But also in time the distinction of before and after must hold; for time and movement always correspond with each other. The before and after in motion identical in substratum with motion yet [20] differs from it in being, and is not identical with motion.
But we apprehend time only when we have marked motion, marking it by before and after; and it is only when we have perceived before and after in motion that we say that time has elapsed. Now we mark them by judging that one thing is [25] different from another, and that some third thing is intermediate to them. When we think of the extremes as different from the middle and the mind pronounces that the ‘nows’ are two, one before and one after, it is then that we say that there is time, and this that we say is time. For what is bounded by the ‘now’ is thought to be time—we may assume this.
[30] When, therefore, we perceive the ‘now’ as one, and neither as before and after in a motion nor as the same element but in relation to a ‘before’ and an ‘after’, no time is thought to have elapsed, because there has been no motion either. On the other hand, when we do perceive a ‘before’ and an ‘after’, then we say that there is [219b1] time. For time is just this—number of motion in respect of ‘before’ and ‘after’.
Hence time is not movement, but only movement in so far as it admits of enumeration. An indication of this: we discriminate the more or the less by number, [5] but more or less movement by time. Time then is a kind of number. (Number, we must note, is used in two ways—both of what is counted or countable and also of that with which we count. Time, then, is what is counted, not that with which we count: these are different kinds of thing.)
[10] Just as motion is a perpetual succession, so also is time. But every simultaneous time is the same; for the ‘now’ is the same in substratum—though its being is different—and the ‘now’ determines time, in so far as time involves the before and after.
The ‘now’ in one sense is the same, in another it is not the same. In so far as it is in succession, it is different (which is just what its being now was supposed to [15] mean), but its substratum is the same; for motion, as was said, goes with magnitude, and time, as we maintain, with motion. Similarly, then, there corresponds to the point the body which is carried along, and 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 is different in definition—as [20] the sophists assume that Coriscus’ being in the Lyceum is a different thing from Coriscus’ being in the market-place. And the body which is carried along is different, in so far 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 [25] before and after in the motion, and if we regard these as countable we get the ‘now’. Hence in these also the ‘now’ as substratum remains the same (for it is what is before and after in movement), but its being is different; for it is in so far as the before and after is that we get the ‘now’. This is what is most knowable; for motion is [30] known because of that which is moved, locomotion because of that which is carried. For what is carried is a ‘this’, the movement is not. Thus the ‘now’ in one sense is always the same, in another it is not the same; for this is true also of what is carried.
[220a1] 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.
[5] Time, then, also is both made continuous by the ‘now’ 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 which is moved, because it is one—not because it is one in substratum (for there might be pauses in the movement of such a thing)—but because it is one in definition; for this determines the movement 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 [10] 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 sense in which there is number of the same [15] 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, both for the reason given (for we can use the middle point as two, so 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 movement, any more than the points are parts of the line—for it is two lines that are [20] parts of one line.
In so far then as the ‘now’ is a boundary, it is not time, but an attribute of it; in so far as it numbers, it is number; for boundaries being only to that which they bound, but number (e.g. ten) is the number of these horses, and belongs also elsewhere.
It is clear, then, that time is number of movement in respect of the before and [25] after, and is continuous since it is an attribute of what is continuous.
The smallest number, in the strict sense, is two. But of number as concrete, sometimes there is a minimum, sometimes not: e.g. of a line, the smallest in respect of multiplicity is two (or, if you like, one), but in respect of size there is no minimum; for every line is divided ad infinitum. Hence it is so with time. In respect [30] of number the minimum is one (or two); in point of extent there is no minimum.
It is clear, too, that time is not described as fast or slow, but as many or few and [220b1] as long or short. For as continuous it is long or short and as a number many or few; but it is not fast or slow—any more than any number with which we count is fast or slow. [5]
Further, there is the same time everywhere at once, but not the same time before and after; for while the present change is one, the change which has happened and that which will happen are different. Time is not number with which we count, but the number of things which are counted; and this according as it occurs before or after is always different, for the ‘nows’ are different. And the [10] number of a hundred horses and a hundred men is the same, but the things numbered are different—the horses for the men. Further, as a movement can be one and the same again and again, so too can time, e.g. a year or a spring or an autumn.
Not only do we measure the movement by the time, but also the time by the [15] movement, because they define each other. The time marks the movement, since it is its number, and the movement the time. We describe the time as much or little, measuring it by the movement, just as we know the number by what is numbered, e.g. the number of
the horses by one horse as the unit. For we know how many horses there are by the use of the number; and again by using the one horse as unit we know the number of the horses itself. So it is with the time and the movement; fo we measure the movement by the time and vice versa. It is reasonable that the [25] should happen; for the movement goes with the distance and the time with the movement, because they are quanta and continuous and divisible. The movement has these attributes because the distance is of this nature, and the time has then because of the movement. And we measure both the distance by the movement an [30] the movement by the distance; for we say that the road is long, if the journey is long; and that this is long, if the road is long—the time, too, if the movement, and the movement, if the time.
Time is a measure of motion and of being moved, and it measures the motion [221a1] by determining a motion which will measure the whole motion, as the cubit does the length by determining an amount which will measure out the whole. Further to be in time means, for movement, that both it and its essence are measured by time (for [5] simultaneously it measures both the movement and its essence, and this is what being in time means for it, that its essence should be measured).
Clearly, then, to be in time has the same meaning for other things also, namely, [10] that their being should be measured by time. To be in time is one of two things: to exist when time exists, and as we say of some things that they are ‘in number’. The latter means either what is a part or mode of number—in general, something which belongs to number—or that things have a number.
Now, since time is number, the ‘now’ and the before and the like are in time, [15] just as unit and odd and even are in number, i.e. in the sense that the one set belongs to number, the other to time. But things are in time as they are in number. If this is so, they are contained by time as things in number are contained by number and things in place by place.
Plainly, too, to be in time does not mean to coexist with time, any more than to [20] be in motion or in place means to coexist with motion or place. For if ‘to be in something’ is to mean this, then all things will be in anything, and the world will be in a grain; for when the grain is, then also is the world. But this is accidental, whereas the other is necessarily involved: that which is in time necessarily involves [25] that there is time when it is, and that which is in motion that there is motion when it is.
Since what is in time is so in the same sense as what is in number is so, a time greater than everything in time can be found. So it is necessary that all the things in time should be contained by time, just like other things also which are in anything, e.g. the things in place by place.
[30] A thing, then, will be affected by time, just as we are accustomed to say that time wastes things away, and that all things grow old through time, and that people forget owing to the lapse of time, but we do not say the same of getting to know or of [221b1] becoming young or fair. For time is by its nature the cause rather of decay, since it is the number of change, and change removes what is.
Hence, plainly, things which are always are not, as such, in time; for they are not contained by time, nor is their being measured by time. An indication of this is [5] that none of them is affected by time, which shows that they are not in time.
Since time is the measure of motion, it will be the measure of rest too. For all rest is in time. For it does not follow that what is in time is moved, though what is in motion is necessarily moved. For time is not motion, but number of motion; and [10] what is at rest can be in the number of motion. Not everything that is not in motion can be said to be at rest—but only that which can be moved, though it actually is not moved, as was said above.
To be in number means that there is a number of the thing, and that its being is [15] measured by the number in which it is. Hence if a thing is in time it will be measured by time. But time will measure what is moved and what is at rest, the one qua moved, the other qua at rest; for it will measure their motion and rest respectively.
Hence what is moved will not be measured by the time simply in so far as it has quantity, but in so far as its motion has quantity. Thus none of the things which are [20] neither moved nor at rest are in time; for to be in time is to be measured by time, while time is the measure of motion and rest.
Plainly, then, neither will everything that does not exist be in time, i.e. those non-existent things that cannot exist, as the diagonal’s being commensurate with the side.
Generally, if time is the measure of motion in itself and of other things [25] accidentally, it is clear that a thing whose being is measured by it will have its being in rest or motion. Those things therefore which are subject to perishing and becoming—generally, those which at one time exist, at another do not—are necessarily in time; for there is a greater time which will extend both beyond their [30] being and beyond the time which measures their being. Of things which do not exist but are contained by time some were, e.g. Homer once was, some will be, e.g. a future event; this depends on the direction in which time contains them; if on both, [222a1] they have both modes of existence. As to such things as it does not contain in any way, they neither were nor are nor will be. These are those non-existents whose opposites always are, as the incommensurability of the diagonal always is—and this [5] will not be in time. Nor will the commensurability, therefore; hence this eternally is not, because it is contrary to what eternally is. A thing whose contrary is not eternal can be and not be, and it is of such things that there is coming to be and passing away.
13 · The ‘now’ is the link of time, as has been said (for it connects past and [10] future time), and it is a limit of time (for it is the beginning of the one and the end of the other). But this is not obvious as it is with the point, which is fixed. It divides potentially, and in so far as it is dividing the ‘now’ is always different, but in so far as it connects it is always the same, as it is with mathematical lines. For the intellect it [15] is not always one and the same point, since it is other and other when one divides the line; but in so far as it is one, it is the same in every respect.
So the ‘now’ also is in one way a potential dividing of time, in another the termination of both parts, and their unity. And the dividing and the uniting are the [20] same thing and in the same reference, but in essence they are not the same.
So one kind of ‘now’ is described in this way: another is when the time of something is near. He will come now, because he will come to-day; he has come now, because he came to-day. But the things in the Iliad have not happened now, nor is the flood now—not that the time from now to them is not continuous, but because they are not near.
[25] ‘At some time’ means a time determined in relation to the first of the two types of ‘now’, e.g. at some time Troy was taken, and at some time there will be a flood; for it must be determined with reference to the ‘now’. There will thus be a determinate time from this ‘now’ to that, and there was such in reference to the past event. But if there be no time which is not ‘sometime’, every time will be determined.
[30] Will time then fail? Surely not, if motion always exists. Is time then always different or does the same time recur? Clearly, it is the same with time as with motion. For if one and the same motion sometimes recurs, it will be one and the same time, and if not, not.
Since the ‘now’ is an end and a beginning of time, not of the same time [222b1] however, but the end of that which is past and the beginning of that which is to come, it follows that, as the circle has its convexity and its concavity, in a sense, in the same thing, so time is always at a beginning and at an end. And for this reason it [5] seems to be always different; for the ‘now’ is not the beginning and the end of the same thing; if it were, it would be at the same time and in the same respect two opposites. And time will not fail; for it is always at a beginning.
‘Just now’ refers to the part of future time which is near the indivisible present [10] ‘now’ (When are you walking?—Just now; because the time in which he
is going to do so is near), and to the part of past time which is not far from the ‘now’ (When are you walking?—I have been walking just now). But to say that Troy has just now been taken—we do not say that, because it is too far from the ‘now’. ‘Lately’, too, refers to the part of past time which is near the present ‘now’. ‘When did you go?’ ‘Lately’, if the time is near the existing now. ‘Long ago’ refers to the distant past.
[15] ‘Suddenly’ refers to what has departed from its former condition in a time imperceptible because of its smallness; but it is the nature of all change to alter things from their former condition. In time all things come into being and pass away; for which reason some called it the wisest of all things, but the Pythagorean Paron called it the most stupid, because in it we also forget; and his was the truer view. It is clear then that it must be in itself, as we said before, a cause of destruction [20] rather than of coming into being (for change, in itself, makes things depart from their former condition), and only accidentally of coming into being, and of being. A sufficient evidence of this is that nothing comes into being without itself moving somehow and acting, but a thing can be destroyed even if it does not move at all. And this is what, as a rule, we chiefly mean by a thing’s being destroyed by time. [25] Still, time does not work even this change; but this sort of change too happens to occur in time.
We have stated, then, that time exists and what it is, and in how many ways we speak of the ‘now’, and what ‘at some time’, ‘lately’, ‘just now’, ‘long ago’, and ‘suddenly’ mean.
14 · These distinctions having been drawn, it is evident that every change [30] and everything that moves is in time; for the distinction of faster and slower exists in reference to all change, since it is found in every instance. In the phrase ‘moving faster’ I refer to that which changes before another into the condition in question, when it moves over the same interval and with a regular movement; e.g. in the case [223a1] of locomotion, if both things move along the circumference of a circle, or both along a straight line; and similarly in all other cases. But what is before is in time; for we say ‘before’ and ‘after’ with reference to the distance from the ‘now’, and the ‘now’ [5] is the boundary of the past and the future; so that since ‘nows’ are in time, the before and the after will be in time too; for in that in which the ‘now’ is, the distance from the ‘now’ will also be. But ‘before’ is used contrariwise with reference to past and to future time; for in the past we call ‘before’ what is farther from the ‘now’, and ‘after’ [10] what is nearer, but in the future we call the nearer ‘before’ and the farther ‘after’. So that since the ‘before’ is in time, and every movement involves a ‘before’, evidently every change and every movement is in time. [15]