The Politics of Aristotle

by Aristotle

  Further, in point of fact things that are thrown move though that which gave them their impulse is not touching them, either by reason of mutual replacement, as [15] some maintain, or because the air that has been pushed pushes them with a movement quicker than the natural locomotion of the projectile wherewith it moves to its proper place. But in a void none of these things can take place, nor can anything be moved save as that which is carried is moved.

  Further, no one could say why a thing once set in motion should stop anywhere; [20] for why should it stop here rather than here? So that a thing will either be at rest or must be moved ad infinitum, unless something more powerful gets in its way.

  Further, things are now thought to move into the void because it yields; but in a void this quality is present equally everywhere, so that things should move in all directions.

  Further, the truth of what we assert is plain from the following considerations. [25] We see the same weight or body moving faster than another for two reasons, either because there is a difference in what it moves through, as between water, air, and earth, or because, other things being equal, the moving body differs from the other owing to excess of weight or of lightness.

  Now the medium causes a difference because it impedes the moving thing, most of all if it is moving in the opposite direction, but in a secondary degree even if [30] it is at rest; and especially a medium that is not easily divided, i.e. a medium that is somewhat dense.

  [215b1] A, then, will move through B in time C, and through D, which is thinner, in time E (if the length of B is equal to D), in proportion to the density of the hindering [5] body. For let B be water and D air; then by so much as air is thinner and more incorporeal than water, A will move through D faster than through B. Let the speed have the same ratio to the speed, then, that air has to water. Then if air is twice as thin, the body will traverse B in twice the time that it does D, and the time C will be [10] twice the time E. And always, by so much as the medium is more incorporeal and less resistant and more easily divided, the faster will be the movement.

  Now there is no ratio in which the void is exceeded by body, as there is no ratio of nought to a number. For if 4 exceeds 3 by 1, and 2 by more than 1, and 1 by still [15] more than it exceeds 2, still there is no ratio by which it exceeds 0; for that which exceeds must be divisible into the excess and that which is exceeded, so that 4 will be what it exceeds 0 by and 0. For this reason, too, a line does not exceed a [20] point—unless it is composed of points. Similarly the void can bear no ratio to the full, and therefore neither can movement through the one to movement through the other, but if a thing moves through the thinnest medium such and such a distance in such and such a time, it moves through the void with a speed beyond any ratio. For let F be void, equal to B and to D. Then if A is to traverse and move through it in a [25] certain time, G, a time less than E, however, the void will bear this ratio to the full. But in a time equal to G, A will traverse the part H of D. And it will surely also traverse in that time any substance F which exceeds air in thinness in the ratio [30] which the time E bears to the time G. For if the body F be as much thinner than D as E exceeds G, A, if it moves through F, will traverse it in a time inverse to the [216a1] speed of the movement, i.e. in a time equal to G. If, then, there is no body in F, A will traverse F still more quickly. But we suppose that its traverse of F when F was void occupied the time G. So that it will traverse F in an equal time whether F be full or void. But this is impossible. It is plain, then, that if there is a time in which it [5] will move through any part of the void, this impossible result will follow: it will be found to traverse a certain distance, whether this be full or void, in an equal time; for there will be some body which is in the same ratio to the other body as the time is to the time.

  To sum the matter up, the cause of this result is obvious, viz. that between any two movements there is a ratio (for they occupy time, and there is a ratio between any two times, so long as both are finite), but there is no ratio of void to full. [10]

  These are the consequences that result from a difference in the media; the following depend upon an excess of one moving body over another. We see that bodies which have a greater impulse either of weight or of lightness, if they are alike in other respects, move faster over an equal space, and in the ratio which their [15] magnitudes bear to each other. Therefore, they will also move through the void with this ratio of speed. But that is impossible; for why should one move faster? (In moving through plena it must be so; for the greater divides them faster by its force. For a moving thing cleaves the medium either by its shape, or by the impulse which the body that is carried along or is projected possesses.) Therefore all will possess [20] equal velocity. But this is impossible.

  It is evident from what has been said, then, that, if there is a void, a result follows which is the very opposite of the reason for which those who believe in a void set it up. They think that if movement in respect of place is to exist, the void must exist, separated by itself; but this is the same as to say that place is separate; and [25] this has already been stated to be impossible.

  But even if we consider it on its own merits the so-called void will be found to be really vacuous. For as, if one puts a cube in water, an amount of water equal to the cube will be displaced, so too in air (but the effect is imperceptible to sense). And indeed always, in the case of any body that can be displaced, it must, if it is not [30] compressed, be displaced in the direction in which it is its nature to be displaced—always either down, if its locomotion is downwards as in the case of earth, or up, if it is fire, or in both directions—whatever be the nature of the inserted body. Now in the void this is impossible; for it is not body; the void must have penetrated the cube to a distance equal to that which this portion of void formerly occupied in the void, just as if the water or air had not been displaced by the wooden cube, but had [216b1] penetrated right through it.

  But the cube also has a magnitude equal to that occupied by the void; a magnitude which, if it is also hot or cold, or heavy or light, is none the less different in essence from all its attributes, even if it is not separable from them; I mean the [5] bulk of the wooden cube. So that even if it were separated from everything else and were neither heavy nor light, it will occupy an equal amount of void, and fill the same place, as the part of place or of the void equal to itself. How then will the body of the cube differ from the void or place that is equal to it? And if there can be two [10] such things, why cannot there be any number coinciding?

  This, then, is one absurd and impossible implication of the theory. It is also evident that the cube will have this same volume even if it is displaced, which is an attribute possessed by all other bodies also. Therefore if this differs in no respect from its place, why need we assume a place for bodies over and above the bulk of each, if their bulk be conceived of as free from attributes? It contributes nothing to [15] the situation if there is an equal interval attached to it as well. [Further, it ought to be clear by the study of moving things what sort of thing void is. But in fact it is found nowhere in the world. For air is something, though it does not seem to be so—nor, for that matter, would water, if fishes were made of iron; for the discrimination of the tangible is by touch.]29

  [20] It is clear, then, from these considerations that there is no separate void.

  9 · There are some who think that the existence of rarity and density shows that there is a void. If rarity and density do not exist, they say, neither can things contract and be compressed. But if this were not to take place, either there would be [25] no movement at all, or the universe would bulge, as Xuthus said, or air and water must always change into equal amounts (e.g. if air has been made out of a cupful of water, at the same time out of an equal amount of air a cupful of water must have been made), or void must necessarily exist; for compression and expansion cannot take place otherwise.

  [30] Now, if they mean by the rare that which has many voids existing separately, it is plain that if void ca
nnot exist separate any more than a place can exist with an extension all to itself, neither can the rare exist in this sense. But if they mean that there is void, not separately existent, but still present in the rare, this is less impossible; yet, first, the void turns out not to be a cause of all movement, but only [217a1] of movement upwards (for the rare is light, which is the reason why they say fire is rare); second, the void turns out to be a cause of movement not as that in which it takes place, but in that the void carries things up as skins by being carried up themselves carry up what is continuous with them. Yet how can void have a local movement or a place? For thus that into which void moves is till then void of a [5] void.

  Again, how will they explain, in the case of what is heavy, its movement downwards? And it is plain that if the rarer and more void a thing is the quicker it will move upwards, if it were completely void it would move with a maximum speed. But perhaps even this is impossible, that it should move at all; the same reason which showed that in the void all things are incapable of moving shows that the void [10] cannot move, viz., the fact that the speeds are incomparable.

  Since we deny that a void exists, but for the rest the problem has been truly stated, that either there will be no movement, if there is no condensation and rarefaction, or the universe will bulge, or a transformation of water into air will always be balanced by an equal transformation of air into water (for it is clear that [15] more air is produced from the water: it is necessary therefore, if compression does not exist, either that the next portion will be pushed outwards and make the outermost part bulge, or that somewhere else there must be an equal amount of water produced out of air, so that the entire bulk of the whole may be equal, or that nothing moves. For when anything is displaced this will always happen, unless it comes round in a circle; but locomotion is not always circular, but sometimes in a [20] straight line)—these then are the reasons for which they might say that there is a void; our statement is based on the assumption that there is a single matter for contraries, hot and cold and the other natural contrarieties, and that what is actually is produced from what is potentially, and that matter is not separable from the contraries but its being is different, and that a single matter may serve for colour [25] and heat and cold.

  The same matter also serves for both a large and a small body. This is evident; for when air is produced from water, the same matter has become something different, not by acquiring an addition to it, but has become actually what it was potentially; and, again, water is produced from air in the same way, the change being sometimes from smallness to greatness, and sometimes from greatness to [30] smallness. Similarly, therefore, if air which is large in extent comes to have a smaller bulk, or becomes greater from being smaller, it is the matter which is potentially both that comes to be each of the two.

  For as the same matter becomes hot from being cold, and cold from being hot, because it was potentially both, so too from hot it can become more hot, though nothing in the matter has become hot that was not hot when the thing was less hot; [217b1] just as, if the arc or curve of a greater circle becomes that of a smaller, whether it remains the same or becomes a different curve, convexity has not come to exist in anything that was not convex but straight (for differences of degree do not depend [5] on an intermission of the quality); nor can we get any portion of a flame, in which both heat and whiteness are not present. So too, then, is the earlier heat related to the later. So that the greatness and smallness, also, of the sensible bulk are extended, not by the matter’s acquiring anything new, but because the matter is potentially matter for both states; so that the same thing is dense and rare, and the [10] two qualities have one matter.

  The dense is heavy, and the rare is light. [Again, as the arc of a circle when contracted into a smaller space does not acquire a new part which is convex, but what was there had been contracted; and as any part of fire that one takes will be hot; so, too, it is all a question of contraction and expansion of the same matter.]30 [15] There are two types in each case, both in the dense and in the rare; for both the heavy and the hard are thought to be dense, and contrariwise both the light and the soft are rare; and weight and hardness fail to coincide in the case of lead and iron.

  From what has been said it is evident, then, that void does not exist either [20] separate (either absolutely separate or as a separate element in the rare) or potentially, unless one is willing to call the cause of movement void, whatever it may be. At that rate the matter of the heavy and the light; qua matter of them, would be the void; for the dense and the rare are productive of locomotion in virtue of this contrariety, and in virtue of their hardness and softness productive of passivity and [25] impassivity, i.e. not of locomotion but rather of qualitative change.

  So much, then, for the discussion of the void, and of the sense in which it exists and the sense in which it does not exist.

  10 · Next for discussion after the subjects mentioned is time. The best plan will be to begin by working out the difficulties connected with it, making use of the [30] current arguments. First, does it belong to the class of things that exist or to that of things that do not exist? Then secondly, what is its nature? To start, then: the [218a1] following considerations would make one suspect that it either does not exist at all or barely, and in the 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 which 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 [5] some of its parts must exist. But of time some parts have been, while others are going to be, and no part of it is, though it is divisible. For the ‘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, the ‘now’ which seems to bound the past and the future—does it always [10] remain one and the same or is it always other and other? It is hard to say.

  If it is always different and different, and if none of the parts in time which are other and other are simultaneous (unless the one contains and the other is contained, as the shorter time is by the longer), and if the ‘now’ which is not, but [15] 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 next to another, any more than a point to a point. If then it did not cease [20] 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 [25] is possible to cut off a determinate time. Further, if coincidence in time (i.e. 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 which happened ten thousand years ago would be simultaneous with what has happened to-day, and nothing would be before or after anything else.

  [30] This may serve as a statement of the difficulties about the attributes of time. As to what time is or what is its nature, the traditional accounts give us as little light as the preliminary problems which we have worked through.

  Some assert that it is the movement of the whole, others that it is the sphere [218b1] itself.

  Yet part, too, of the revolution is a time, but it certainly is not a revolution; for what is taken is part of a revolution, not a revolution. Besides, if there were more heavens than one, the movement of any of them equally would be time, so that there [5] wou
ld be many times at the same time.

  Those who said that time is the sphere of the whole thought so, no doubt, on the ground that all things are in time and all things are in the sphere of the whole. The view is too naive for it to be worth while to consider the impossibilities implied in it.

  [10] But as time is most usually supposed to be motion and a kind of change, we must consider this view.

  Now the change or movement of each thing is only in the thing which changes or where the thing itself which moves or change may chance to be. But time is present equally everywhere and with all things.

  Again, change is always faster or slower, whereas time is not; for fast and slow [15] are defined by time—fast is what moves much in a short time, slow what moves little in a long time; but time is not defined by time, by being either a certain amount or a certain kind of it.

  Clearly then it is not movement. (We need not distinguish at present between movement and change.) [20]

  11 · But neither does time exist without change; for when the state of our minds does not change at all, or we have not noticed its changing, we do not think that time has elapsed, any more than those who are fabled to sleep among the heroes in Sardinia do when they are awakened; for they connect the earlier ‘now’ with the [25] later and make them one, cutting out the interval because of their failure to notice it. So, just as, if the ‘now’ were not different but one and the same, there would not have been time, so too when its difference escapes our notice the interval does not seem to be time. If, then, the non-realization of the existence of time happens to us when we do not distinguish any change, but the mind seems to stay in one indivisible [30] state, and when we perceive and distinguish we say time has elapsed, evidently time is not independent of movement and change. It is evident, then, that time is neither [219a1] movement nor independent of movement.