Aristotle · a new plain-English translation from the original language
1| The matter both perishes and comes to be — in one sense, yes, in another, no. For as that in which the privation resides, it perishes in its own right (for what perishes, the privation, is present in it). But as understood in respect of potentiality, it does not perish in its own right; rather, it must necessarily be imperishable and ungenerated. For if it came to be, there would have to be some primary underlying thing already present in it, out of which it came to be — but this is precisely its own nature, so that it would exist before it came to be (for I call matter the primary underlying thing for each thing, present in it, out of which something comes to be, not accidentally). And if it perishes, it will arrive, as its final stage, at this very thing, so that it will have perished before it perished. As for the principle that corresponds to form — whether it is one or many, and what it is or what they are — determining this with precision is the task of first philosophy; so let it be reserved for that occasion, and we will speak about the natural and perishable forms among the things demonstrated later. That there are principles, then, and what they are, and how many in number — let this stand as our determination. Let us begin again from another starting point and speak. B.
2| Of the things that exist, some exist by nature, others through other causes. By nature: animals and their parts, plants, and the simple bodies — earth, fire, air, and water (for we say that these and things like them exist by nature), and all of these plainly differ from things not constituted by nature. For each of these has within itself a principle of motion and rest — some in respect of place, some in respect of growth and decay, some in respect of alteration. A bed, on the other hand, or a cloak, or any other class of thing of that sort, insofar as it falls under each such predicate and to the extent that it is a product of craft, has no innate impulse to change at all; but insofar as it happens to be made of stone or earth or a mixture of these, it does have such an impulse, and only to that extent — nature being a certain principle and cause of being moved and being at rest, present primarily in that in which it belongs in its own right and not accidentally (I say "not accidentally" because a person who is a doctor might become the cause of health to himself; but even so, it is not insofar as he is being healed that he has medical knowledge — rather, it is accidental that the same person is both a doctor and someone being healed;
3| which is why the two are sometimes found apart from one another). The same holds, similarly, for each of the other things that are made: none of them has within itself the principle of its own making. Rather, in some cases the principle is in something else and external — as with a house and each of the other things made by hand — while in others it is within the thing itself, but not in its own right, namely in all the cases where the thing might become, accidentally, a cause to itself. Nature, then, is what has been described; and a thing has a nature if it has a principle of this kind. And all such things are substance; for each is some underlying subject, and nature is always present in an underlying subject. In accordance with nature are these things themselves, and whatever belongs to them in their own right — for instance, fire's moving upward; for this is not itself a nature, nor does it have a nature, but it exists by nature and in accordance with nature. What nature is, then, has been stated, and also what "by nature" and "in accordance with nature" mean. To try to prove that nature exists is ridiculous; for it is obvious that many things of this kind exist. And to try to prove what is obvious by means of what is not obvious marks someone incapable of distinguishing what is known through itself from what is not known through itself (that it is possible to be in this condition is not hard to see —
4| someone blind from birth might reason about colors) — so that people of this sort are necessarily engaged in argument about mere words, understanding nothing. To some, the nature and substance of things that exist by nature seems to be the primary constituent present in each thing, unshaped in its own right — for instance, wood is the nature of a bed, bronze the nature of a statue. Antiphon offers as a sign of this that if one were to bury a bed and the rot gained enough power to send up a shoot, what would come to be would not be a bed but wood — on the ground that the arrangement in accordance with convention and craft belongs to it only accidentally, while its substance is that other thing which persists continuously through undergoing these very processes. And if each of these materials in turn stands in this same relation to some further thing (bronze and gold, for instance, in relation to water; bones and wood in relation to earth; and likewise for anything else whatever), then that further thing is their nature and substance. That is why some say fire, others earth, others air, others water, others some of these, and others all of them, are the nature of the things that exist. For whichever of these each thinker took to be of this kind — whether one or several — this, and just this many, he says the whole of substance is, while everything else he says is an affection, state, or condition of these; and any one of these he says is eternal (for there is no change of them out of themselves), while everything else comes to be and perishes endlessly.
5| In one way, then, nature is spoken of in this sense — as the primary matter underlying each thing that has within itself a principle of motion and change; in another way, as the shape and the form given in the definition. For just as "craft" is used of what accords with craft and what is craftsmanlike, so too "nature" is used of what accords with nature and what is natural. And in the former case we would not yet say that a thing has anything in accordance with craft if it is only potentially a bed and does not yet have the form of a bed, nor that craft is present in it; nor is it so among things constituted by nature: what is only potentially flesh or bone does not yet have its own nature until it takes on the form given in the definition, by reference to which, in defining it, we say what flesh or bone is — nor does it yet exist by nature. So in another sense, the nature of things that have within themselves a principle of motion would be the shape and the form — not separable except in definition. (What is composed of matter and form together is not itself a nature, but exists by nature — a human being, for instance.) And this form is nature more than the matter is; for each thing is called by its name more when it exists in realization than when it exists in potentiality. Furthermore, a human being comes to be from a human being, but a bed does not come to be from a bed —
6| which is why they say it is not the shape but the wood that is the nature, on the ground that if it were to sprout, what would result would not be a bed but wood. But if that is nature, then form too is nature; for a human being comes to be from a human being. Furthermore, the nature spoken of as coming-to-be is a path toward a nature. For it is not as with medical treatment, which is said to be a path not toward medical craft but toward health — treatment necessarily proceeds from medical craft, not toward medical craft; nature, however, is not related to nature in this way, but rather what grows proceeds from something toward something, in the very respect in which it grows. What, then, is it that grows? Not that from which, but that into which. The form, therefore, is nature. But "form" and "nature" are each spoken of in two ways; for privation too is, in a way, a form. Whether there is privation, and something contrary, in unqualified coming-to-be, or whether there is not, must be examined later.
7| Now that we have distinguished the senses in which nature is spoken of, we must next examine how the mathematician differs from the student of nature (for natural bodies too have surfaces, solids, lengths, and points, which are what the mathematician studies); and further, whether astronomy is different from natural science or a part of it. For it would be absurd for the student of nature to know what the sun or the moon is, but none of the attributes that belong to them in their own right — especially since writers on nature are seen discussing the shape of the moon and the sun as well, and indeed whether the earth and the universe are spherical or not. Now these matters are treated by the mathematician too, but not insofar as each is the boundary of a natural body; nor does he study the attributes as belonging to such bodies. That is why he separates them out — for they are separable in thought from motion, and it makes no difference, nor does any falsehood result from separating them. Those who speak of the Forms do the same thing without noticing it; for they separate natural things, which are less separable than mathematical objects. This would become clear if one tried to define each of the two — the objects themselves and their attributes. For odd and even, straight and curved, and also number, line, and figure will be definable without motion; but flesh, bone, and man will not — these are spoken of as 'snub nose' is, not as 'curved' is. The more physical branches of mathematics show this too, such as optics, harmonics, and astronomy; for these stand in a way opposite to geometry. Geometry investigates natural lines, but not insofar as they are natural, while optics investigates a mathematical line, but not insofar as it is mathematical — rather, insofar as it is natural.
8| Since nature is spoken of in two ways — as form and as matter — we must study it as we would if we were investigating what snubness is: such things must be treated neither apart from matter nor purely in terms of matter. Indeed one might raise a difficulty about this very point: since there are two natures, which of the two does the study of nature concern? Or does it concern what is composed of both? But if it concerns what is composed of both, then it concerns each of the two as well. Is it then the same knowledge, or a different one, that knows each? Looking to the ancients, one might suppose the study belongs to matter (for Empedocles and Democritus laid hold of form and essence only to a small degree); but if craft imitates nature, and it belongs to the same knowledge to know the form and the matter, up to a point (for instance, it belongs to the doctor to know health, and also bile and phlegm, in which health resides; and likewise it belongs to the builder to know both the form of the house and the matter — that it is bricks and timber; and so on with the rest), then it would belong to natural science to know both natures as well. Further, the end and that for the sake of which belong to the same knowledge, and so do whatever serves these ends. Now nature is an end and that for the sake of which — for whenever there is continuous motion toward some end, that final point is also the end, that for the sake of which;
9| that is why the poet was ridiculously carried away when he said, 'it has the end for the sake of which it came to be' — for he means that not every final point is an end, but only the best one) — and since, further, the crafts make their matter, some simply, others so as to make it serviceable, and we use all things as though they existed for our sake (for we too are in a way an end; for that for the sake of which is spoken of in two ways, and this has been discussed in the works on philosophy). There are two crafts that govern matter and have knowledge of it: the using craft, and, within the productive craft, the master craft. That is why the using craft is in a way a master craft too; but they differ in that the master craft knows the form, while the other, as merely productive, knows the matter. For the helmsman knows and prescribes what sort of form the rudder should have, while the shipbuilder knows out of what wood, and by what motions, it will be made. So in the products of craft we make the matter for the sake of the work, while in natural things the matter is already present. Further, matter is relative: for different matter belongs to different form. To what point, then, must the student of nature know the form and the essence? Is it as the doctor must know sinew, or the smith bronze — up to the point of knowing that for the sake of which each exists, and concerning those things that are separable in form but exist in matter? For man begets man, and so does the sun. But how the separable exists, and what it is, is the task of first philosophy to determine.
11| Now that these points have been settled, we must go on to examine the causes — what kinds there are and how many in number. For since our undertaking is for the sake of knowing, and we do not think we know a thing until we have grasped the why of it in each case (and this is to grasp its primary cause), clearly we too must do this concerning coming-to-be and perishing and every kind of natural change, so that, knowing their principles, we may try to refer each of the things under inquiry back to them. In one sense, then, that out of which a thing comes to be, and which persists in it, is called a cause — for instance, the bronze of the statue, and the silver of the bowl, and the genera to which these belong. In another sense, the cause is the form or the pattern — that is, the account of the essence, and the genera of this (for instance, the ratio two to one, and number generally, are the cause of the octave), and the parts that appear in the account. Again, a cause is that from which the primary source of change or of rest arises — for instance, the one who deliberated is a cause, and the father is the cause of the child, and in general the maker is a cause of the thing made, and what brings about change is a cause of what is changed. Again, a cause is spoken of as the end — that is, that for the sake of which, as health is the cause of walking. For why does someone walk? We say, 'in order to be healthy,' and in saying this we think we have given the cause. And so too are all the things that come between, once something else has set them in motion toward the end — as, in the case of health, thinning, purging, drugs, or instruments; for all of these are for the sake of the end, though they differ from one another in that some are actions and others instruments.
12| The causes, then, are spoken of in about this many ways. But since causes are spoken of in many ways, it follows that there can be several causes of the same thing, and not accidentally — for instance, both the sculptor's craft and the bronze are causes of the statue, not in virtue of anything else but in virtue of being a statue, though not in the same way: the one as matter, the other as the source of motion. There are also things that are causes of one another — for instance, exertion is a cause of good condition, and good condition is a cause of exertion; but not in the same way, the one as end, the other as source of motion. Again, the same thing is a cause of opposites; for what, by its presence, is the cause of a given thing, we sometimes hold responsible, by its absence, for the opposite — for instance, we say the helmsman's absence caused the capsizing of the ship, when his presence would have been the cause of its safety. All the causes now mentioned fall under four principal headings, the most evident of these. For the letters are causes of syllables, and the matter is a cause of manufactured things, and fire and the like are causes of bodies, and the parts are causes of the whole, and the premises are causes of the conclusion, in the sense of that out of which; but of these, some are causes as the underlying subject (for instance, the parts), while others are causes as the essence — the whole, the combination, and the form. The seed, the doctor, the one who deliberated, and in general the agent, are all causes in the sense of that from which the source of change or of rest arises. Others are causes as the end, and as the good of the rest; for that for the sake of which tends to be the best, and the end of the other things. And let it make no difference whether we call it the good itself, or the apparent good.
13| These, then, are the causes, and this many in form; but the modes of the causes are many in number, though these too, when summed up, are fewer. For a cause is spoken of in many ways, and even among causes of the same kind, one is prior and another posterior to another—for example, of health, the physician and the craftsman more generally; and of the octave, the double ratio and number; and always the encompassing things are causes relative to the particulars they encompass. Again, a thing is a cause as an accident, and so are the genera of these—for example, Polyclitus is a cause of the statue in one way, and the sculptor in another, because it is accidental to the sculptor to be Polyclitus. And the things that encompass the accident are also causes—for example, if a human being is the cause of a statue, or, more generally, an animal. And among accidents too, some are further off and some nearer—for example if the pale and the musical were said to be causes of the statue. And all of these—both the ones spoken of in their own right and the ones spoken of accidentally—are spoken of either as being causes in potentiality or as being causes in actuality; for example, the builder is a cause of a house being built, or the builder who is actually building. And the same will be said in the case of the things of which these are the causes—for example, of this statue, or of a statue, or of an image in general; and of this bronze, or of bronze, or of matter in general; and likewise for the accidents.
14| Again, these and those will also be spoken of as combined—for example, not Polyclitus, nor the sculptor, but Polyclitus the sculptor. But all the same, all of these are six in number, though spoken of in two ways: either as the particular, or as the genus, or as the accident, or as the genus of the accident, or as these combined, or as spoken of simply; and all of them either as actual or as potential. And they differ to this extent, that the actual causes and the particular causes exist and cease to exist together with the things of which they are causes—for example, this one who is healing together with this one who is being healed, and this one who is building together with this one who is being built—whereas the potential causes do not always. For the house and the builder do not perish together. And one must always look for the highest cause of each thing, just as in other cases too (for example, a human being builds because he is a builder, and the builder builds in virtue of the craft of building; this, then, is the prior cause, and so in all cases); again, genera are causes of genera, and particulars of particulars (for example, the sculptor is cause of the statue, and this one of this one); and potentialities are causes of possible things, and actual things of things being actualized. Let this, then, be an adequate account for us of how many the causes are, and in what way they are causes.
15| Chance and spontaneity are also said to be among the causes, and many things are said both to exist and to come to be through chance and through spontaneity; we must therefore examine in what way chance and spontaneity are among these causes, and whether chance and spontaneity are the same or different, and, generally, what chance and spontaneity are. For some are even puzzled as to whether they exist or not; for they say that nothing at all comes to be from chance, but that there is some definite cause for everything we say comes to be from spontaneity or chance—for example, of someone's coming by chance into the marketplace and meeting the person he wished to meet but did not expect to, the cause is his wishing to go and buy something; and likewise in the other cases said to be from chance, one can always find some cause, but not chance—since if chance really were something, it would truly appear strange, and one might well be puzzled as to why none of the ancient sages, in stating the causes of coming-to-be and passing-away, determined anything about chance, but, as it seems, they too thought nothing came to be from chance. But this too is remarkable.
16| For many things both come to be and exist from chance and from spontaneity, and people are not unaware that it is possible to trace each of the things that come to be back to some cause—as the old argument that does away with chance put it—yet all the same they say that some of these are from chance and others are not from chance; and that is why they had, in some way or other, to make some mention of it. But then again, they did not think chance was any of the things they posited either—love, or strife, or intellect, or fire, or anything else of that kind. So it is strange, whether they supposed it did not exist, or supposed it did and left it out of their accounts—and this though they sometimes actually made use of it, as Empedocles does when he says that air is not always separated out uppermost, but however it happens to occur. At any rate he says in his cosmogony that “thus it chanced to run at that time, but often otherwise”; and he says that most of the parts of animals came to be by chance. And there are some
17| who ascribe both this heaven and all the worlds to spontaneity; for they say that the vortex and the motion that separated things out and settled the universe into this order arose from spontaneity. And this very thing is quite remarkable to wonder at: for while they say that animals and plants neither exist nor come to be by chance, but that the cause is nature, or intellect, or something else of that sort (for it is not whatever happens to result from each seed, but from this kind of seed an olive tree, and from that kind a human being), they say that the heaven and the most divine of visible things came to be from spontaneity, and that there is no cause of that sort for them such as there is for animals and plants. And yet, if this is so, this very point is worth pausing over, and it would be well to say something about it. For besides the fact that what is said is strange in other ways too, it is stranger still to say this while observing that nothing comes to be from spontaneity in the heaven, whereas among the things that are not from chance, many things happen by chance—although it would be reasonable for the opposite to occur. And there are some who think that chance is indeed a cause, but that it is unclear to human thinking, as being something divine and more supernatural. So we must examine what each of the two is, and whether spontaneity and chance are the same or different, and how they fall among the causes we have distinguished.
18| First, then, since we see that some things always come to be in the same way, and others for the most part, it is clear that chance is not said to be the cause of either of these—neither of what is of necessity and always, nor of what is for the most part. But since there are things that come to be even apart from these, and all say that these are from chance, it is clear that chance and spontaneity are something; for we know that such things are from chance, and that things from chance are of this sort. Now, among things that come to be, some come to be for the sake of something and others do not (and of these, some are in accordance with choice and some not in accordance with choice, but both kinds are among the things that are for the sake of something); so it is clear that even among the things that occur apart from what is necessary and what is for the most part, there are some in connection with which it is possible for there to be something for the sake of which. And things are for the sake of something whenever they might be done as a result of thought, and whenever they result from nature. Such things, then, whenever they come to be accidentally, we say are from chance (for just as a thing may be in its own right or accidentally, so too a cause may be; for example, the cause of a house in its own right is the housebuilding craft, but accidentally it is the pale, or the musical—
19| A cause in its own right is determinate, while an accidental cause is indeterminate; for an unlimited number of things might happen to the one thing. As we said, then, whenever this occurs among things that come about for the sake of something, it is said to happen from spontaneity or from chance (we must determine later how these two differ from each other; for now let this much be clear, that both belong among things that occur for the sake of something): for example, he would have come to get his money back from the man collecting the loan-fund, if he had known this — but he did not come for this reason; rather, it turned out that he came, and that he did this for the sake of recovering the money. And this was not something that happens to him, in frequenting that place, either for the most part or of necessity. And the end — the recovery of the money — is not among the causes within the man himself, but among the things chosen and coming from thought. And in that case he is said to have come by chance; but if he had chosen it and gone for this very purpose, either always or for the most part, it would not be by chance. It is clear, then, that chance is a cause accidentally, among things done by choice for the sake of something. This is why thought and chance are concerned with the same thing; for choice does not occur without thought.
20| The causes, then, from which
21| what happens by chance might come about must be indeterminate. This is why chance too is thought to belong to the indeterminate, and to be unclear to a human being, and why it might seem, in a way, that nothing happens by chance at all. For all these things are said correctly, and with good reason. For in one sense it is true that things do happen by chance: they happen accidentally, and chance is a cause in the sense of an accidental cause; but in the unqualified sense it is the cause of nothing. For example, the builder is the cause of a house, but the flute-player is its cause only accidentally; and the causes of a man's having come and recovered his money, when he did not come for this purpose, are unlimited in number — for he may have come wanting to see someone, or in pursuit of someone, or in flight from someone, or going to watch a spectacle. And it is also correct to say that chance is something contrary to reasonable expectation; for an account concerns either what always is or what is for the most part, and chance belongs among the things that come about apart from these. So then, since causes of this kind are indeterminate, chance too is indeterminate. All the same, in some cases one might raise a puzzle: are just any chance things the causes of a chance event — for instance, of health, wind or exposure to the sun, but not having had one's hair cut? For some accidental causes are nearer than others. Chance is called good when something good results from it, and bad when something bad results; and good fortune and misfortune are spoken of when these have some magnitude. This is also why missing a great evil or a great good by a narrow margin counts as good fortune or misfortune — because thought speaks of it as though it already belonged, since what is missed by a narrow margin seems to be no distance away at all. Further, it stands to reason that good fortune is unstable, since chance is unstable; for none of the things that come about by chance can occur either always or for the most part. Both, then, as has been said, are accidental causes — both chance and spontaneity — among things that admit of coming about neither in an unqualified way nor for the most part, and, among these, whichever ones might come about for the sake of something.
22| They differ in that spontaneity extends more widely: everything that is by chance is also from spontaneity, but not everything from spontaneity is by chance. For chance, and what is by chance, belong only to those beings to whom good fortune, and action in general, could belong. This is why chance is also necessarily concerned with things that can be done — a sign of this is that good fortune is thought to be either the same as happiness or close to it, and happiness is a kind of action, since it is doing well — so that whatever cannot act cannot do anything by chance either. And this is why nothing lifeless, and no beast, and no child does anything by chance, because none of them has choice; nor does good fortune or misfortune belong to them, except by resemblance, as Protarchus said that the stones out of which altars are made are fortunate, because they are honored, while the stones from the very same quarry-bed are trampled underfoot. But even these can, in a sense, be affected by chance, whenever someone acting upon them does something to them by chance — otherwise it cannot happen. But spontaneity belongs also to the other animals, and to many lifeless things as well: for instance, we say the horse came spontaneously, meaning that its coming saved it, though it did not come for the sake of being saved;
23| and the tripod fell spontaneously, for it stood there for the sake of being sat on, but it did not fall for the sake of being sat on. So it is clear that among things that come about, in the unqualified sense, for the sake of something, whenever the cause lies outside them and the thing does not come about for the sake of what actually resulted, then we call it spontaneous; and by chance, whenever such spontaneous events occur among the things that could have been chosen, in beings that have choice. A sign of this is the word 'in vain,' which is used whenever the thing that is for the sake of something else does not come about for the sake of that other thing — for example, if walking is for the sake of a purge, and this did not happen as a result of the walking, we say the walking was in vain and the walk was a vain one, as though this were what 'in vain' means: something whose nature is for the sake of something else, whenever it does not achieve that for the sake of which it existed and for which it was naturally suited — since if someone said he bathed in vain because the sun was not eclipsed, he would be ridiculous, for the bath was not for the sake of that. So too spontaneity is named accordingly, whenever it itself comes about in vain: the stone, for instance, did not fall for the sake of striking someone; the stone therefore fell spontaneously, because it might have been made to fall by someone, and for the sake of striking someone. Spontaneity is most clearly set apart from chance in things that come about by nature; for whenever something comes about contrary to nature, we say then that it has come about not by chance but rather spontaneously. And this too is a further difference: in the one case the cause is external, in the other, internal.
24| What spontaneity is, then, and what chance is, has been stated, and how they differ from each other. As for the modes of causation, each of the two belongs among the things from which the origin of motion comes; for the cause is always either one of the natural causes or one of the causes that come from thought, but the number of these is indeterminate. And since spontaneity and chance are causes of whatever intellect or nature might be the cause of, whenever something becomes a cause of these very things accidentally — and nothing accidental is prior to what is in its own right — it is clear that the accidental cause is not prior to the cause in its own right either. Spontaneity and chance are therefore posterior to both intellect and nature. So that even if spontaneity is, in the highest degree, the cause of the heavens, it is still necessary that intellect and nature be prior causes, both of many other things and of this universe as well. That there are causes, and that they are just as many in number as we say, is clear; for the question 'why' comprehends just this many answers. For the 'why,' in the last resort, is traced back either to the what-it-is, in the case of unchanging things (as in mathematics — it is traced back, in the last resort, to the definition of the straight, or the commensurable, or something else), or to what first set something in motion (for example, why did they go to war? Because they had been plundered), or to that for the sake of which (in order that they might rule), or, in the case of things that come to be, to the matter.
25| That the causes are these, then, and just this many, is clear.
26| Since the causes are four, it is the business of the natural philosopher to know about all of them, and referring the question "why" to all of them, he will give the explanation in the manner proper to natural science — the matter, the form, the mover, and that for the sake of which. Three of these often coincide in one: for the what-it-is and that for the sake of which are one, and the primary source of motion is the same in form as these. For man begets man — and in general this holds of everything that, being itself moved, causes motion (whatever does not move in this way no longer belongs to natural science; for such things move without having motion in themselves, nor a principle of motion, but being themselves unmoved. That is why there are three branches of study: one concerning unmoved things, one concerning things that are moved but imperishable, and one concerning perishable things). So the "why" is given both by referring to the matter, and to what the thing is, and to the primary mover. For it is especially in inquiries about coming-to-be that causes are examined in this way — what comes after what, and what acted first or what was first acted on, and so on always in sequence. The principles that produce motion in the natural way are twofold, and one of them is not itself natural; for it does not have a principle of motion in itself. Such is whatever moves without itself being moved, as the wholly unmoved and first of all things is, and also what a thing is and its shape; for these are an end and that for the sake of which. So, since nature is for the sake of something, this cause too must be known, and the "why" must be given in every way — for instance, that from this, this necessarily follows (and "from this" either without qualification or for the most part); and that, if this is going to be, that must follow from it (just as the conclusion follows from the premises); and that this was the essence; and because it is better this way — not better without qualification, but better relative to the substance of each thing.
27| We must state, then, first, that nature belongs among the causes that act for the sake of something; and next, concerning the necessary, how it stands in the things of nature. For everyone refers explanation to this cause — to the necessary — saying that since the hot is naturally of such a kind, and the cold, and each such thing, these other things are and come to be of necessity. Indeed, even when they do mention some other cause, they touch on it only in passing and let it go — one mentioning love and strife, another intellect. But there is a puzzle here: what prevents nature from acting not for the sake of something and not because it is better, but as Zeus rains not in order to make the grain grow, but of necessity (for what is drawn up must cool, and what has cooled, having become water, must come down; and it is a mere consequence that the grain grows when this happens)? Likewise, if someone's grain is ruined on the threshing floor, it does not rain for the sake of ruining it — that is merely a coincidence. So what prevents the parts of the body from being like this too — for instance, that the front teeth necessarily grow sharp, suited for cutting, and the molars broad and useful for grinding food, not because they came to be for this purpose, but because it just turned out that way? And likewise for the other parts, in all the cases where purpose seems to be present. So wherever everything turned out just as it would have if it had come to be for a purpose, these survived, having been suitably put together by spontaneity; but whatever was not put together in this way perished and goes on perishing, just as Empedocles says of his "man-faced ox-progeny."
28| This, then, is the argument by which someone might raise the puzzle, and any other argument of the same kind; but it is impossible for things to be this way. For these things, and everything that is by nature, come to be either always in this way or for the most part, but nothing that results from chance or spontaneity does. For we do not think it is by chance or coincidence that it rains often in winter, but rather if it rains often under the Dog Star; nor that there is heat under the Dog Star, but rather if there is heat in winter. If, then, things are held to be either by coincidence or for the sake of something, and if it is not possible for these things to be either by coincidence or by spontaneity, they would be for the sake of something. But surely all such things are by nature, as even the very people who make this argument would themselves admit. The for-the-sake-of-something, then, is present in things that come to be and exist by nature.
29| Further, in all cases where there is some end, the earlier step and the one that follows are done for the sake of that end. So as a thing is done, that is how it is naturally constituted to be done, and as it is naturally constituted, so each thing is done — unless something impedes it. But it is done for the sake of something; therefore it is also naturally constituted for the sake of something. For example, if a house were one of the things that come to be by nature, it would come to be just as it now does by craft; and if things that come to be by nature came to be not only by nature but also by craft, they would come to be in just the way they are naturally constituted to come to be. Each, then, is for the sake of the other. And in general craft, in some cases, completes what nature is unable to bring to completion, and in others imitates nature. If, then, the products of craft are for the sake of something, clearly so are the products of nature; for the later stages stand in the same relation to the earlier both in things done by craft and in things that occur by nature. This is most evident in the case of the other animals,
30| which act neither by craft nor after inquiring nor after deliberating — which is why some raise the puzzle whether spiders and ants and creatures of that sort work by intellect or by something else. And proceeding a little further along these lines, in plants too the things that are useful for the end are seen to come about — for instance, the leaves grow for the sake of shelter for the fruit. So if the swallow makes its nest, and the spider its web, both by nature and for the sake of something, and plants produce their leaves for the sake of their fruit and send their roots down, not up, for the sake of their nourishment, it is clear that this kind of cause is present among things that come to be and exist by nature. And since nature is spoken of in two ways, as matter and as form, and the form is the end, and everything else is for the sake of the end, this — the form — would be the cause in the sense of that for the sake of which. Now error occurs even in the products of craft (for the grammarian wrote incorrectly, and the doctor administered the medicine wrongly). So it is clear that error is possible in the products of nature as well. If, then, there are cases in the arts where what is done correctly is for the sake of something, and in cases of error the attempt is likewise for the sake of something but fails to achieve it, the same would hold in the products of nature, and monstrosities would be failures in that aiming at an end. So too, in the original formations of things, the "ox-progeny" — if they were unable to arrive at some determinate limit and end — must have come about through the corruption of some starting principle, just as now happens with the seed.
31| Further, it is necessary that seed should come to be first, and not the animals themselves at once; and the "whole-natured, first" was seed. Further, purposiveness is present in plants too, though less articulated. Did there then also occur in plants, just as there were man-faced ox-progeny, also olive-faced vine-progeny? Or not? For that is absurd. And yet there ought to have been, if indeed there were in the case of animals. Further, on this view chance combinations ought to have occurred among the seeds too. But in general, whoever argues this way does away with both natural things and nature itself. For things are by nature whatever, moving continuously from some principle within themselves, arrive at some end; and from each starting principle the outcome is not the same for every kind of thing, nor is it a chance outcome, but it always tends toward the same result, unless something impedes it. Now that for the sake of which, and what exists for the sake of it, could also come about by chance — for instance, we say that the stranger came by chance and, after paying his ransom, went away, when he acts as if he had come for this purpose, though he did not come for the sake of it. And this is accidental (for chance belongs among the accidental causes, as we said before); but when something happens always or for the most part, it is not accidental nor the result of chance — and in the case of natural things it always happens this way, unless something impedes it.
32| It is absurd to think that something does not come to be for the sake of something, just because we do not see the mover deliberating. And yet craft, too, does not deliberate. If shipbuilding were present in the wood itself, it would produce its effects in the same way as nature does. So if the for-the-sake-of-something is present in craft, it is present in nature as well. This is most evident when someone doctors himself, for in this case nature resembles craft. That nature, then, is a cause, and a cause in this way — as acting for the sake of something — is clear.
33| But does what is of necessity hold on a hypothesis, or without qualification as well? As things stand, people suppose that necessity is present in coming-to-be in the way that someone might suppose a wall has come to be of necessity, on the ground that heavy things are naturally carried downward and light things to the surface — which is why the stones and the foundations are below, the earth is above because of its lightness, and the timbers are most of all on the surface, since they are the lightest of all. But nevertheless it has not come to be without these, though not because of these, except as through matter — it has come to be for the sake of sheltering and protecting certain things. Similarly too in all the other cases in which there is a for-the-sake-of-something: they do not come to be without the things that have a necessary nature, yet not because of these, except as matter — they come to be for the sake of something. For example: why is the saw such as it is? So that it may perform this function, for the sake of that. But this end cannot come about unless the saw is made of iron; it is therefore necessary for it to be of iron, if there is to be a saw and its function. The necessary, then, holds on a hypothesis, not as an end in itself; for the necessity lies in the matter, while that for the sake of which lies in the account.
34| The necessary is present, in a certain way, similarly both in mathematics and in things that come to be by nature. Since the straight line is what it is, it is necessary that the triangle have angles equal to two right angles; but it is not because of this that the straight line is what it is — yet if this does not hold, the straight line does not hold either. In things that come to be for the sake of something, however, it is the reverse: if the end is to be, or is, then what comes before it is to be, or is, as well; and if not, then — just as there, when the conclusion does not hold, the starting-point does not hold either — so here too the end, that for the sake of which, will not hold. For this too is a starting-point, not of the action but of the reasoning (and there too it is a starting-point of the reasoning only, since there are no actions in mathematics). So if there is to be a house, it is necessary for these things to come to be or be present, or for the matter that is for the sake of something to exist at all — bricks and stones, say, if there is to be a house. Yet the end does not exist because of these, except as matter, nor will it come to be because of these. And yet without these existing at all, there will be neither the house nor the saw — the house not without the stones, the saw not without the iron. For neither, in mathematics, will the starting-points hold, if the triangle does not have two right angles.