Aristotle · a new plain-English translation from the original language
1| B. 1 On mixture, then, and contact, and acting and being acted on, we have said how these belong to things that change according to nature; and further, concerning generation and destruction — both unqualified generation and generation of a particular thing (the wording of this clause is disputed among the manuscripts and editors; the variants recorded do not affect the sense) — how these are, and through what cause. Likewise we have also spoken about alteration: what being altered is, and what differentiates it from these other changes. It remains to consider the so-called elements of bodies. For generation and destruction belong to all substances constituted by nature, and not without perceptible bodies; and as for the matter underlying these, some say it is one — positing air, for instance, or fire, or something intermediate between them, being a body and separable — while others say it is more than one in number: some say fire and earth, others these together with air as a third, and others again water as a fourth besides these, as Empedocles does; and they hold that generation and destruction happen to things out of these, as they combine and separate, or are altered.
2| That it is right to call the primary things principles and elements, let this be agreed — those things from whose change, whether by combination and separation or by some other kind of change, generation and destruction come about. But those who posit a single matter besides the things mentioned, and make this matter corporeal and separable, are mistaken. For it is impossible for this body, being perceptible, to exist without contrariety; this unlimited thing which some say is the principle must be either light or heavy, either cold or hot. But as it is written in the Timaeus, no definition is given of it; for he has not said clearly whether the all-receiving thing is separate from the elements. Nor does he make any use of it, even though he says there is something underlying prior to the so-called elements, as gold underlies works made of gold. And yet even this is not well said, put in this way; rather, for things of which there is alteration, it holds in this way, but for things of which there is generation and destruction, it is impossible for that from which they came to be called by the same name. And yet he says it is far truest to call each thing gold. But since the elements are solids, he carries the analysis down only as far as planes; and it is impossible for the nurse and the primary matter to be planes.
3| We, however, say that there is some matter of perceptible bodies, but that this matter is not separable, but is always accompanied by contrariety, and it is out of this that the so-called elements come to be. This has been determined more precisely elsewhere. Nevertheless, since it is in this way that the primary bodies come from matter, we must give a determination about these as well, for those who suppose that the inseparable matter — that which underlies the contraries — is the first and primary principle. For neither is the hot matter for the cold, nor is the cold matter for the hot, but what underlies both of them is. So that, first, the potentially perceptible body is a principle; second, the contrarieties — I mean, for example, heat and cold; and third, already, fire and water and things of that sort. For these change into one another, and not in the way Empedocles and others say (for then there would be no alteration), while the contrarieties themselves do not change. But none the less we must also say, as regards body, of what kind and how many the principles are to be called; for the others assume them and use them, and say nothing about why they are these or why they are this many.
4| 2 Since, then, we are seeking the principles of perceptible body, and this is tangible, and the tangible is that of which the perception is touch, it is clear that not all contrarieties produce forms and principles of body, but only those that go by touch. For things differ by contrariety, and specifically by tangible contrariety. This is why neither whiteness and blackness, nor sweetness and bitterness, nor likewise any of the other perceptible contrarieties, produces an element. And yet sight is prior to touch, so that its underlying subject is prior too. But this is not an affection of tangible body qua tangible, but in some other respect, even if it happens to be prior in nature. We must, then, first divide among the tangible qualities themselves which are the primary differentiae and contrarieties. The contrarieties that go by touch are these: hot–cold, dry–wet, heavy–light, hard–soft, viscous–brittle, rough–smooth, coarse–fine. Of these, heavy and light are neither active nor passive; for they are not so called by acting on something else or by being acted on by something else. But the elements must be active and passive with respect to one another, for they mix and change into one another. Hot and cold and wet and dry, however, are called some of them active and some passive:
5| for hot is that which combines things of the same kind (for the separating that they say fire does is really a combining of things akin to one another; the effect is to remove what is foreign), while cold is that which draws together and combines alike both things akin and things not of the same kind; wet is that which, being unbounded, is easily bounded by an external boundary; dry is that which is easily bounded by its own boundary, but hard to bound by an external one. Fine and coarse, viscous and brittle, hard and soft, and the other differentiae, arise from these. For since what is capable of filling up gaps belongs to the wet, because it is not bounded but is easily bounded and follows whatever touches it, and the fine is capable of filling up gaps (for it consists of fine parts, and what consists of small parts is capable of filling up gaps, since whole touches whole throughout, and the fine is especially of this sort), it is clear that the fine will belong to the wet, and the coarse to the dry. Again, the viscous belongs to the wet (for the viscous is a wet thing that has undergone a certain affection, as oil is), and the brittle belongs to the dry; for the brittle is what is completely dry, so that it has also solidified through lack of moisture. Further, the soft belongs to the wet (for the soft is what yields into itself and does not displace, which is what the wet does;
6| and this is why the wet is not itself soft, but the soft belongs to the wet), while the hard belongs to the dry; for the hard is what has solidified, and what has solidified is dry. But dry and wet are spoken of in more than one way; for opposed to the dry are both the wet and the damp, and again opposed to the wet are both the dry and the solidified; and all of these belong to the dry and the wet in the primary sense already stated. For since the dry is opposed to the damp, and the damp is that which has an alien moisture on its surface, while the drenched is that which has it in depth, and the dry is that which is deprived of this, it is clear that the damp will belong to the wet, while the dry opposed to it belongs to the dry in the primary sense. Again, the wet and the solidified stand in the same way: the wet is that which has moisture of its own, the drenched is that which has an alien moisture in depth, and the solidified is that which is deprived of this. So that of these too, one will belong to the dry, the other to the wet. It is clear, then, that all the other differentiae are reduced to these primary four. And these are no longer reducible to fewer; for the hot is not simply the wet or simply the dry, nor is the wet simply the hot or simply the cold, nor are the cold and the dry either under one another or under the hot and the wet;
7| So there must necessarily be these four. 3 Since there are four elements, and of the four there are six possible pairings, but opposites are not naturally paired together (for it is impossible for the same thing to be both hot and cold, or again both dry and wet), it is clear that there will be four pairings of the elements: hot with dry, hot with wet, cold with wet, and cold with dry. And this follows, in due proportion, upon the simple bodies that appear to our senses, fire, air, water, and earth: for fire is hot and dry, air is hot and wet (since air is, as it were, vapor), water is cold and wet, and earth is cold and dry. So it is reasonable that the differentiae should be distributed among the primary bodies in this way, and that their number should correspond in due proportion. For of all who make the simple bodies elements, some make one, some two, some three, some four. Now those who speak of only one, and then generate the rest by condensation and rarefaction, end up in effect positing two principles, the rare and the dense, or the hot and the cold; for these are what do the working, while the one is set down as their underlying matter. Those who straightaway posit two, as Parmenides posits fire and earth, make the things between them mixtures of these two, namely air and water. And likewise
8| those who speak of three, as Plato does in his divisions: for he makes the middle term a mixture. And those who posit two and those who posit three say more or less the same thing, except that the latter divide the middle term into two, while the former make it only one. Some, however, straightaway speak of four, as Empedocles does; yet even he reduces them to two, since he sets everything else in opposition to fire. But fire and air and each of the things named are not in fact simple, but mixed; the simple bodies are of that character, but are not identical with them — for instance, whatever is like fire is fire-like, not fire, and what is like air is air-like; and similarly with the rest. Fire is an excess of heat, just as ice is an excess of cold; for solidifying and boiling are each a kind of excess, the one of cold, the other of heat. If, then, ice is the solidifying of what is wet and cold, fire will be the boiling of what is dry and hot. That is why nothing comes to be either out of ice or out of fire. Since the simple bodies are four, each of the two pairs belongs to one of the two regions: fire and air belong to what moves toward the boundary, earth and water to what moves toward the center. Fire and earth are the extremes and the most unmixed, while water and air are intermediate and more mixed. And each pair is opposite to the other: water is opposite to fire, and earth to air; for these are constituted out of opposite affections. Nevertheless, taken simply, each of the four is characterized by one quality more than the other: earth is more dry than cold, water is more cold than wet, air is more wet than hot, and fire is more hot than dry.
9| 4 Since it has already been determined that the simple bodies come to be out of one another, and at the same time they are evidently observed by perception to come to be (for otherwise there would be no alteration, since alteration is in respect of the affections of the tangible), we must state the manner of their change into one another, and whether it is possible for everything to come to be from everything, or whether it is possible for some and not for others. That all naturally change into one another is clear: for generation is into opposites and out of opposites, and all the elements have opposition to one another because their differentiae are opposite; for in some pairs both qualities are opposite, as with fire and water (the one being dry and hot, the other wet and cold), while in others only the one quality is opposite, as with air and water (the one being wet and hot, the other wet and cold). So it is clear in general that everything is naturally capable of coming to be out of everything; but it is not hard to see, case by case, how this happens: everything will come to be out of everything, but they will differ in being quicker or slower, and easier or harder.
10| For whatever things share features with one another, the transition between them is quick; whatever do not, is slow, because it is easier for one thing to change than for many. For example, out of fire will come air, when one of the two features changes (fire was hot and dry, air is hot and wet, so that if the dry is overcome by the wet, it will be air); and again out of air comes water, if the hot is overcome by the cold (for air was hot and wet, water is cold and wet, so that when the hot changes, it will be water). In the same way, out of water comes earth, and out of earth, fire; for these too share features with each other in pairs: water is wet and cold, earth is cold and dry, so that when the wet is overcome, it will be earth. And again, since fire is dry and hot, and earth is cold and dry, when the cold is destroyed, fire will come from earth. So it is clear that generation will go round in a circle for the simple bodies, and that this is the easiest manner of change, because shared features exist between things next to each other in the series.
11| But it is also possible for water to come from fire, and earth from air, and again for air and fire to come from water and earth, though this is harder, because the change involves more factors: for necessarily, if fire is to come from water, both the cold and the wet must be destroyed, and again if air is to come from earth, both the cold and the dry must be destroyed. Likewise too, if water and earth are to come from fire and air, both must change. This generation, then, takes longer. But if, of each pair, one quality is destroyed, the change is easier, though it is not a change into one another directly, but rather earth and air will come from fire and water, and fire and water will come from air and earth. For when the cold is destroyed out of water and the dry out of fire, it will be air (for what is left over is the hot from the one and the wet from the other); and when the hot is destroyed out of fire and the wet out of water, it will be earth, because what is left over is the dry from the one and the cold from the other. Likewise too, fire and water come from air and earth: when the hot is destroyed out of air and the dry out of earth, it will be water (for what is left is the wet from the one and the cold from the other); and when the wet is destroyed out of air and the cold out of earth, it will be fire, because what is left over is the hot from the one and the dry from the other, which are exactly what belongs to fire.
12| The generation of fire in this way is also confirmed by perception: for flame is fire above all, and flame is smoke burning, and smoke is composed of air and earth. But among things next to each other in the series it is not possible, when one of the pair of elements is destroyed on each side, for a transition to occur into any of the bodies, because what is left over in both is either the same quality or opposite qualities. And a body cannot come to be out of either of these: for instance, if the dry were destroyed out of fire and the wet out of air, what is left over in both is the hot; and if the hot were destroyed out of each, what is left over are the opposites, dry and wet. The same holds in the other cases too; for in all pairs next to each other, one quality is the same in both and the other is opposite. So it is at once clear that things pass from one into one only. It has now been said that everything comes to be out of everything, and in what manner the change into one another takes place.
13| 5 Nevertheless, let us examine these matters further in this way too. For if there is a matter of the natural bodies, as some think — water and air and the like — these must be either one, or two, or more. Now they cannot all be one — for instance, all air, or all water, or all fire, or all earth — if indeed change is into contraries. For if it were air, then if it persists as air, there will be alteration but not generation. But at the same time it does not even seem to be so, that a thing should be water and air at once, or anything else at all. There will then be some contrariety and differentia of which one part — fire, say — will possess something, for instance heat. But surely fire will not be hot air; for a thing of that kind would be alteration, and it does not appear to be so. Again, at the same time, if air is to come from fire, this will happen by the hot changing into its contrary. This contrary will then belong to air, and air will be something cold. So it is impossible for fire to be hot air; for the same thing would then be at once hot and cold. Both fire and air, then, will be something else, the same thing, and there will be some other, common matter. And the same argument holds concerning all of them: that none of these is the one thing out of which all things come.
14| Nor again is it some other thing besides these — something midway between air and water, say, or between air and fire, thicker than air and fire but thinner than the others; for that thing will be air and fire together with a contrariety, and privation is one member of a pair of contraries, so that thing could never exist by itself alone, as some say of the unlimited and the surrounding body. Likewise, then, it will be one of these, or none of them. If, then, nothing perceptible is prior to these, these would be all there is. It is necessary, then, either that they remain always and are unchangeable into one another, or that they change — and either all of them, or some but not others, as Plato wrote in the Timaeus. That they must change into one another, then, has been shown before. And that one does not come from another equally quickly has also been said before: that things having a common feature come from each other more quickly, and those not having one, more slowly. If, then, there is one contrariety in respect of which they change, they must be two; for the matter, the middle term, being imperceptible
15| and inseparable, does not itself figure as a further member. But since more than two are seen to exist, the fewest there could be is two. And if there are two, there cannot be three, but four, as indeed appears to be the case; for that is the number of the pairings — with six possible, two of the pairings cannot occur, because those two members are contrary to each other. Now this has been said before. But that, since they change into one another, it is impossible for any of them to be a starting principle, whether at an extreme or in the middle, is clear from the following. It will not be at the extremes, because then everything would be fire or earth — and the same argument applies to saying that everything comes from fire or from earth. And that it is not the middle term either is also clear — as some think, that air changes both into fire and into water, and water both into air and into earth, but the extreme terms no longer change into one another. For the series must come to a stop and not proceed to infinity along the line in either direction; otherwise there will be infinite contrarieties on the one continuum. Let G stand for earth, Y for water, A for air, P for fire. If, then, A changes into P and into Y, there will be a contrariety between A and P.
16| Let these be whiteness and blackness. Again, if A changes into Y, there will be another contrariety; for Y and P are not the same. Let this be dryness and wetness — X being dryness, Y being wetness. Now if white persists, water will be wet and white; but if not, water will be black, since change is into contraries. Water, then, must be either white or black. Let it be the former. Likewise, then, X — dryness — will belong to P as well. There will then also be a change for fire into water; for it possesses the contraries — fire was first black, then dry, while water is wet, then white. It is clear, then, that there will be change from each into each of them, and in their case at least, that the remaining qualities will belong there too, and that black and wet are two common features not yet paired together. That it is not possible to proceed to infinity — which was the very point we set out to prove when we arrived at this — is clear from the following. For again, if fire, P, changes into something else and does not turn back, say into Q, there will be some other contrariety between fire and Q, different from those already mentioned;
17| for Q underlies none of the same things as G, Y, A, P. Let K belong to P, and let F belong to Q. K, then, will belong to all of G, Y, A, P, since they change into one another. But let this be granted as not yet demonstrated; still this much is clear, that if Q in turn changes into something else, another contrariety will belong both to Q and to fire, P. And so on always: along with what is added, some contrariety will belong to the earlier terms as well, so that, if the terms are infinite, infinite contrarieties will belong to the one element. And if this is so, it will be impossible either to define anything or for anything to come to be; for it will be necessary, if one thing is to come from another, to run through that many contrarieties, and more besides, so that for some pairs there will never be change at all — if, say, the intermediate terms are infinite, which they must be, if the elements are infinite. Further, there will be no change even from air to fire, if the contrarieties are infinite. And everything becomes one; for it is necessary that all the contrarieties belonging to the terms above P belong also to those below it, and that those belonging to the terms below belong to those above, so that everything will be one.
18| 6 One might well wonder, in the case of those who say the elements of bodies are more than one and so do not change into one another, as Empedocles says, how they can consistently say that the elements are commensurable with one another. And yet he does speak this way: 'for all these are equal.' Now if they are commensurable in respect of quantity, there must be some one and the same thing present in all the commensurable things by which they are measured — for instance, if a pint of water yielded ten pints of air, then in a way both were the same thing, if they are measured by the same unit. But if they are not commensurable in this way in respect of quantity, as quantity measured against quantity, but rather in respect of how much they can do — for instance, if a pint of water can cool as much as ten pints of air — then in this sense they are commensurable not as quantity, but as having a certain power. But it might also be that their powers are compared not by a measure of quantity at all, but by analogy — as, for example, this is to white as that is to hot. And 'as this' signifies, in the case of quality, the similar, and in the case of quantity, the equal. It appears absurd, then, if bodies that are unchangeable are commensurable not by analogy, but by a measure of their powers — by being of equal heat, or of similar heat, so much of fire matching a many-times-greater amount of air —
19| For that same thing, by being of the same kind, will have this account when it is greater. But in fact there could not be growth at all on Empedocles' view, except by addition; for fire grows by fire: "earth increases its own kind, and aether increases aether." But these things are merely added; and the things that grow do not seem to grow in this way. It is much harder to give an account of natural generation. For everything that comes to be by nature comes to be either always or for the most part, while what falls outside the always and the for-the-most-part comes to be from the automatic and from luck. What, then, is the cause of a human coming from a human either always or for the most part, and of wheat coming from wheat but not an olive—or again, of bone being put together in this particular way? For nothing comes to be, as he says, from things simply coming together however it happens, but according to some ratio. What, then, is the cause of these things? For it is certainly not fire or earth. But neither is it Love and Strife; for one of these is the cause only of combination, the other only of separation. This is the substance of each thing, not merely "a mixing and interchange of things mixed," as he says.
20| In these cases it is called chance, not a rational account; for it is possible for things to be mixed however it happens. Now for things that exist by nature, the cause is their being so, and this is the nature of each thing—about which he says nothing. So he says nothing about nature at all. Moreover, this natural constitution is also well and good; but he praises only the mixing. And yet it is not Strife that separates out the elements but Love, elements that are by nature prior to the god; and these too are gods. Further, he speaks of motion without qualification; for it is not enough to say that Love and Strife cause motion, unless it belonged to the being of Love to produce motion of this particular kind, and to Strife of that kind—he ought to have defined it, or laid it down as a hypothesis, or demonstrated it, whether precisely or loosely, or in some way at least. Further, since bodies plainly move both by force and against nature, and also according to nature—for instance fire moving upward is not by force, but downward it is by force, and what is by force is opposed to what is according to nature, and being-by-force does exist—so motion according to nature also exists. Does Love, then, move this? Or not? For on the contrary, it seems that it is Love that moves earth upward and by force, and it is Strife rather than Love that is the cause of motion according to nature.
21| So that, on the whole, Love would rather be the cause of motion against nature. And simply put, if it is not Love or Strife that causes motion, then there is no motion at all in the bodies themselves, nor any rest—but that is absurd. Further, they are plainly in motion: Strife separated things out, and the aether was carried upward not by Strife—rather, at one point he says it happened as if by chance ("for so it chanced to run at that time, though often otherwise"), and at another point he says it is fire's nature to be carried upward, while the aether, he says, "sank down along the earth with long roots." At the same time he also says the world is in the same condition now, under Strife, as it was earlier under Love. What, then, is the first mover and cause of motion? For surely it is not Love and Strife themselves—rather, these are the causes of some particular motion; but if a first mover exists, that is a principle. It is also absurd if the soul is composed of the elements, or is one of them; for how will the alterations of the soul come about—for instance, being musical and then again unmusical, or memory or forgetting? For it is clear that if the soul is fire, it will have all the affections that belong to fire as fire;
22| and if it is a mixture, it will have bodily affections; but none of these alterations of the soul is bodily. But an inquiry into these matters is the work of a different study. As for the elements out of which bodies are composed: for those who hold that there is something common to them, or that they change into one another, it necessarily follows that if one of these claims holds, the other holds as well; but for those who do not make generation occur out of one another, nor treat each element as coming from the others—except in the way bricks come from a wall—it is absurd how flesh and bones and any of the other things will come to be out of them. And what has been said involves a difficulty
23| also for those who generate the elements out of one another: in what way does something other than these come to be from them? I mean, for instance, that water comes from fire and fire from water (for there is something common underlying both), but also flesh and marrow come to be from them—how do these come to be? For those who speak as Empedocles does, what way will there be? For there must necessarily be composition, just as a wall is composed of bricks and stones; and this mixture will consist of the elements preserved intact, but arranged together in small portions next to one another. Thus, then, flesh and each of the other things are composed. Now it follows that fire and water do not come from just any part of flesh whatsoever, in the way that, from wax, a sphere might come from this part and a pyramid from another part—yet it was at least possible for either shape to come from either part of the wax. This, then, is how it happens with flesh: both fire and water come from any part whatsoever. But for those who speak in that other way this is not possible—rather, as with a stone and a brick from a wall, each comes from a different place and part. Similarly, for those who make the matter of the elements a single thing, there is also a certain difficulty: how will something come to be out of both, for instance out of cold and hot, or fire and earth?
24| For if flesh comes from both and is neither of them, nor again a composition in which they are preserved intact, what is left except that what comes from them is matter? For the destruction of one of the two produces either the other or the matter. Is it, then, because there is a more and a less of hot and cold, that when one of them is present in actuality without qualification, the other will be present potentially; but when it is not present completely, but rather it is hot in a way that is cold, and cold in a way that is hot (because in mixing they destroy each other's excesses), then it will be neither the matter nor, without qualification, either of those contraries in actuality, but something in between? And in proportion as it is potentially more hot or cold, or the reverse, on this reckoning it will be, say, twice as hot potentially as cold, or three times as hot, or in some other such ratio. The other things, then, will come to be, when mixed, out of the contraries or out of the elements, and the elements out of these contraries, since they exist in a way potentially—not in the way matter does, but in the manner stated; and in this way it is a mixture, but in the other way what comes to be is matter. And since each also undergoes the action of its contrary, according to the distinction made at the outset: for what is actually hot is potentially cold, and what is actually cold is potentially hot, so that if they are not equal, they change into one another (and likewise with the other contraries too), and it is in this way that the elements first change; and from these, flesh and bones and such things come to be, the hot becoming cold and the cold becoming hot, when it arrives at the mean;
25| for here neither extreme is present, but the middle is broad and not indivisible. And in the same way the dry and the wet and the like produce flesh and bone and the rest by a mean. 8 All the compound bodies that exist around the region of the middle are composed out of all the simple bodies. For earth is present in all of them because each thing is present most of all and in greatest amount in its own proper place; and water is present because the compound must have a boundary, and water alone among the simple bodies is easily bounded, and further because earth by itself cannot hold together without the wet, but it is this that holds it together — for if the wet were removed from it entirely, it would fall apart. Earth, then, and water are present for these causes; air and fire are present because they are contrary to earth and water — for earth is contrary to air, and water to fire, so far as it is possible for one substance to be contrary to another. Since, then, comings-to-be are out of contraries, and one of the extremes of each pair of contraries is present, the other must be present too, so that in every compound all the simple bodies will be present. The nourishment of each kind of thing seems to bear this out too: everything is nourished by the same things it is made of, and everything is nourished by more than one thing. Indeed even what would seem to be nourished by one thing alone — plants, by water — are nourished by more than one; for earth is mixed with the water, which is why farmers try to water their crops with a mixture. Since nourishment belongs to the matter, while what is nourished, taken together with the
26| matter, is shape and form, it is reasonable that among the simple bodies fire alone should be nourished, all the others coming to be out of one another, as the earlier thinkers also say. For fire alone, or fire most of all, belongs to the form, because it is fire's nature to travel toward the boundary. And each thing has a nature to travel to its own region; and the shape and form of all things lie in their boundaries. That all bodies, then, are composed out of all the simple bodies has now been stated.
27| 9 Since some things are subject to coming-to-be and passing away, and coming-to-be occurs in the region around the middle, we must speak, with respect to every coming-to-be alike, of how many and what its principles are; for we shall study particular cases more easily in this way, once we have first grasped the universal account. The principles are equal in number and the same in kind as those in the case of the eternal and primary things; for one is, as it were, matter, and the other, as it were, form. But a third principle must also be present in addition; for the two are not sufficient to produce generation, just as they are not sufficient in the case of the primary things either. As matter, then, the cause for things subject to generation is that which is capable of being and of not being. For some things exist of necessity, as the eternal things do, while other things do not exist of necessity. Of these latter, some cannot possibly not exist, and others cannot possibly exist, because it is not possible for what is necessary to be otherwise. But some things are capable both of being and of not being, and this is precisely what is subject to coming-to-be and passing away; for at one time such a thing exists, and at another it does not exist. So coming-to-be and passing away must concern what is capable of being and of not being.
28| For this reason, as matter, this is the cause for things subject to generation, while as that for the sake of which, it is the shape and the form; and this is the account of the substance of each thing. But a third principle must also be present, which everyone dreams of but no one states, though some have thought the nature of the forms a sufficient cause for coming-to-be, as does the Socrates of the Phaedo — for he too, having found fault with the others for saying nothing, lays it down as a hypothesis that among existing things some are forms and others share in the forms, and that each thing is said to be in virtue of the form, and to come to be in virtue of a taking-on, and to pass away in virtue of a casting-off, so that, if these things are true, he thinks the forms must of necessity be causes both of coming-to-be and of passing away. Others make matter itself the cause, since motion comes from it. But neither party speaks well. For if the forms are the causes, why do they not generate continuously and always, rather than sometimes doing so and sometimes not, given that both the forms and the things sharing in them exist always? Moreover, in some cases we observe that the cause is something else: the doctor produces health, and the man of knowledge produces knowledge, even though health itself and knowledge itself, and the things that share in them, also exist;
29| and likewise in the other cases of things done through a capacity. If someone should say that it is the matter that generates, on account of motion, he would speak more in the manner of a student of nature than those who speak as above; for what alters and what reshapes is more truly a cause than what generates in name only, and in all cases we are accustomed to call this — whatever is capable of causing motion — the agent, alike among things that come to be by nature and among things that come to be by craft. Yet these thinkers too are not right. For it belongs to matter to be acted on and to be moved, while to move and to act belongs to a different capacity. This is clear both in the products of craft and in the products of nature: water does not of itself make an animal out of itself, nor does wood make a bed, but craft does. So these thinkers too are wrong on this account, and because they leave out the more authoritative cause; for they take away the essence and the shape. Further, they assign to bodies, in a very mechanical way, the capacities by which they generate, doing away with the cause that operates according to the form. For since, as they say, it is the nature of the hot to separate out and of the cold to make things cohere, and of each of the other qualities in the same way to act or to be acted on, they say that all the rest come to be and pass away out of these and through these;
30| yet fire itself is observed to be moved and to be acted on. Further, what they do is much like someone attributing to the saw, and to each of the other tools, the cause of the things that come to be by their use; for it is necessary that what is being sawn be divided, and what is being planed be smoothed, and likewise with the rest. So even granting that fire acts and moves as much as possible, they fail to see how it moves — namely, worse than the tools do. We ourselves have spoken earlier, in general terms, about the causes, and now we have given a determinate account concerning both the matter and the form.
31| 10 Further, since it has been shown that motion in respect of locomotion is eternal, it necessarily follows, these things being so, that coming-to-be too is continuous; for the locomotion will produce coming-to-be unceasingly, by bringing the generative body near and taking it away again. At the same time it is clear that what was said earlier was said rightly — that locomotion, and not coming-to-be, is the first of the changes. For it is far more reasonable that what exists should be the cause of coming-to-be for what does not exist, than that what does not exist should be the cause of being for what exists. Now what is being carried along exists, while what is coming to be does not exist; and this is why locomotion is prior to coming-to-be. Since it has been laid down and shown that coming-to-be and passing away are continuous in the world of things, and since we say that locomotion is the cause of coming-to-be, it is clear that, there being only one locomotion, both cannot come to be, because they are contraries; for what is the same and in the same condition is naturally suited always to produce the same effect. So either coming-to-be will always occur, or passing away will. But the motions must be more than one, and contrary to one another, either in their path or in their irregularity; for contrary effects have contrary causes. That is why it is not the primary locomotion that is the cause of coming-to-be and passing away, but the motion along the oblique circle —
32| For in this it is that both continuity holds and there is being-moved by two motions; for necessarily, if generation and corruption are always to be continuous, something must always be in motion, so that these changes may not fail, and by two motions, so that not only one of the two results occurs. Now the cause of the continuity is the motion of the whole, while the cause of its coming near and going away is the inclination; for it happens that the sun is at one time far off and at another near. And since the interval is unequal, the motion will be irregular; so that if by coming near and being close it generates, then by going away and this same motion becoming far off it destroys, and if by approaching many times it generates, then also by departing many times it destroys; for of contraries the causes are contrary. And the corruption and the generation that occur according to nature take place in an equal time. This is why the times and the lives of each thing have a number and are marked off by this; for all things have an order, and every life and time is measured by a period, though not all by the same period, but some by a lesser and some by a greater; for to some a year, to others a longer, to others a shorter period is the measure. And this is seen to agree, according to perception too, with the accounts we have given.
33| For we see that when the sun approaches there is generation, and when it departs there is decay, and each occupies an equal time; for the time of the corruption and of the generation that occur according to nature is equal. But it often happens that things perish in a shorter time because of their mixing with one another; for since the matter is irregular and not everywhere the same, the generations too must necessarily be irregular, some quicker and some slower, so that it happens, because of the generation of these, that corruption comes about for others. And always, as has been said, generation and corruption will be continuous, and will never fail, for the reason we have stated. This has come about reasonably; for since we say that in all things nature always reaches for the better, and being is better than not being (in how many senses we speak of being has been said elsewhere), and since it is impossible for this to hold in all things because of their being far removed from the principle, god filled up the whole in the remaining way, by making generation continuous; for in this way being would best be strung together, because coming-to-be and generation always are nearest to substance. And the cause of this, as
34| has been said many times, is the circular motion; for it alone is continuous. This is why the other things too, all those that change into one another according to their affections and their powers, for example the simple bodies, imitate the circular motion; for when air comes to be out of water, and fire out of air, and again water out of fire, we say that the generation has gone round in a circle, because it turns back again. So that straight motion too, imitating the circular, is continuous. And at the same time it is clear from this what some people are puzzled about, namely why, since each of the bodies is carried to its own proper place, the bodies have not become separated from one another in infinite time. For the cause of this is their passing over into one another; for if each remained in its own place and were not changed by its neighbor, they would already have been separated. Now they change because of the motion's being twofold; and because of this changing it is not possible for any of them to remain in any place assigned to it. So then, that there is generation and corruption, and for what cause, and what the generable and the perishable is, is clear from what has been said. But since it is necessary that there be something that moves, if there is to be motion, as has been said before elsewhere, and if the motion is to be always, that something must always be, and if it is to be continuous, this must be one and the same, and unmoved and ungenerated and unalterable, and if the circular motions are more than one, however many there are, they must all somehow be under a single principle.
35| And since time is continuous, motion too must necessarily be continuous, if indeed it is impossible for time to exist apart from motion; time, then, is the number of something continuous, namely of the circular motion, just as was determined in the accounts at the beginning. And is the motion continuous because the thing moved is continuous, or because that in which it is moved is continuous — I mean, for example, the place, or the affection? It is clear that it is because the thing moved is continuous; for how could the affection be continuous, except because the thing to which it belongs is continuous? And if it is also because of that in which the motion occurs, this belongs only to place; for place has a certain magnitude, and of this only the circular is continuous, so that it is always continuous with itself. This, then, is what makes the motion continuous, namely the body carried in a circle; and the motion measures the time.
36| 11 Since in things that are continuously moved, whether in generation or alteration or change in general, we see the sequence, one thing coming to be after another so that there is no gap, we must examine whether there is something that will necessarily be, or whether nothing is necessary, but everything admits of not coming to be. That some things are necessary is clear, and immediately the difference between "will be" and "is going to be" shows this; for what it is true to say will be, this must at some time be true to say is; but what it is now true to say is going to be, nothing prevents from not coming to be — for someone who is going to walk might not walk. And in general, since some of the things that are admit also of not being, clearly the things that come to be will be in the same condition, and this will not be of necessity. Is it then the case that all things are of this sort, or not, but rather that some things necessarily come to be without qualification, and, just as with being some things are incapable of not being and others are capable, so too is it with coming to be? For example, must solstices necessarily come to be, and is it not possible for this not to happen? If then it is necessary for the earlier thing to come to be, given that the later thing will be — for example, if there is to be a house, a foundation, and if this, then clay —
37| does it then follow that, if a foundation has come to be, a house must necessarily come to be? Or not any longer, unless that too is necessary without qualification; but if it is, then it is also necessary that, once the foundation has come to be, the house come to be; for this was the relation the earlier thing had to the later, such that if the latter is to be, the former is necessarily prior. If, then, the later thing must necessarily come to be, the earlier thing too is necessary; and if the earlier thing is necessary, then the later thing is necessary too, but not on account of that earlier thing, but because it was posited as going to be of necessity. In cases, then, where the later thing must be, in these the relation converts, and always, once the earlier thing has come to be, the later thing must come to be. If, then, it goes on to infinity downward, the later thing, this particular one, will not be necessary without qualification. Nor will it be necessary even on a hypothesis; for there will always necessarily be some other, earlier thing, on account of which that thing must come to be. So that if there is no starting point of the infinite series, there will not be any first thing either, on account of which it will be necessary for the thing to come to be. But then neither in cases that do have a limit will it be possible to say truly that it is necessary without qualification for the thing to come to be, for example a house, once a foundation has come to be; for when it has come to be, if it is not always necessary for this to happen, it will result that what admits of not always being will always be.
38| But there must always be generation of it, if its generation is of necessity; for the necessary and the always go together; for what must be cannot not be; so that if it is of necessity, it is eternal, and if it is eternal, it is of necessity. And so if the generation of a thing is of necessity, the generation of this thing is eternal, and if it is eternal, it is of necessity. If, then, the generation of something is of necessity without qualification, it must revolve in a circle and turn back again. For it is necessary either that the generation have a limit or not, and if not, either that it go in a straight line or in a circle. And of these, if it is to be eternal, it cannot go in a straight line, because there is nowhere a starting point, neither below, as we take it with respect to things that are going to be, nor above, as with respect to things that have come to be; but there must be a starting point, since it is not unlimited, and it must be eternal. This is why it must be in a circle. It is necessary, then, that the relation convert, for example, if this thing is of necessity, then the earlier thing too; but then, if this, the later thing too must come to be. And this holds always, continuously; for it makes no difference whether we speak of it through two things or through many. In circular motion and generation, then, is found what is of necessity without qualification.
39| And if it is in a circle, each thing must both come to be and have come to be, and if it is necessary, then the coming-to-be of these things is in a circle. This is reasonable enough, since it was shown, on other grounds too, that circular motion, and that of the heaven, is eternal, because these things come to be and will be of necessity — as many motions as belong to this motion, and as many as occur because of it. For if what moves in a circle always moves something else, then the motion of these other things too must be in a circle: for example, since the motion of the region above is circular, the sun moves as it does; and since the sun is so, the seasons for this reason come to be in a circle and turn back again; and since these come to be in this way, again the things caused by these do too. Why then is it that some things plainly do this — for instance water and air coming to be in a circle, and if there is to be a cloud, it must rain, and if it is to rain, there must also be a cloud — while human beings and animals do not turn back into themselves so as to become the same one again? For it is not necessary, if the father came to be, that you should come to be; but if you came to be, it is necessary that he did. This coming-to-be seems rather to run in a straight line. The starting point of the inquiry, again, is this: whether all things turn back alike, or not, but some in number and others only in species.
40| Of those things, then, whose moved substance is imperishable, it is clear that they will be the same in number too (for the motion follows upon what is moved); but of those whose substance is not imperishable but perishable, they must turn back in species, though not in number. This is why water out of air and air out of water are the same in species, not in number. And even if these too are the same in number, this is nevertheless not so for those things whose substance comes to be being of such a kind as to admit of not being.