Part II: The Classical Period

D. Aristotle's Philosophy of Nature

The bulk of the writings of Aristotle is devoted to the philosophy of nature which, of course, he in no way distinguishes from the science of nature. In pursuing the study of nature, Aristotle shows himself to be uncommonly interested in everything his predecessors had to say, making use of their opinions and findings at almost every step of the exposition of his own doctrine. We should not expect, however, that Aristotle is interested in the mere enumeration of previous opinions. He quite consciously uses his predecessors as stepping stones to what he takes to be the truth of the matter. We would be well advised to look on this not as a cavalier abuse of historical truth, but as a way of taking seriously the intent of earlier thinkers. Aristotle's assumption is that whoever talked about nature was not merely providing biographical data, but was concerned with explaining the way things are. If the explanations break down for reasons that can be shown, the positions can still be used for establishing the truth of the matter. Thus, for Aristotle, not every mobile thing is alive and no divine thing is mobile in the proper sense of the term. If this is so, the use of statements of a philosopher who thought that the basic stuff of things is God-Soul-Matter is going to entail ignoring certain aspects of a statement and concentrating on those aspects relevant to a particular consideration. Aristotle is always less interested in what an author intended to say than he is in a statement's relation to what the author intended to talk about.

The first problem the science of nature faces, Aristotle seems to think arises from the fact that its possibility had been denied by Parmenides and, somewhat differently, by Plato. As Aristotle makes clear, this is really a problem that the philosophy of nature cannot solve: for natural science to answer fundamental attacks on itself is for it be in a position similar to that of the man painting the eaves of a two-story house when his partner tells him to get a good grip on his brush because he is taking away the ladder. Despite this, Aristotle feels constrained to discuss Parmenides at the very outset of the Physics; his reply to Plato we will reserve for the proper arena for such disputes, metaphysics. A problem more peculiar to natural philosophy has to do with its order of procedure; we will turn immediately to Aristotle's doctrine on this point.

Order of Procedure. In pursuing scientific knowledge of nature, as in any other scientific pursuit, we are after an explanation of the subject in terms of its principles, causes and elements. We observe the world around us, we wonder why it is what it is and as it is, and our wonder is dispelled when we can assign reasons. In saying this, Aristotle may be thought to he making explicit what is implicit in the endeavors of his predecessors. He goes on to make an important distinction.

What we must not fail to recognize, he insists, is that what we first come to know about the natural world and in terms of which give our first explanations of it, must not be identified with that in nature which is most properly the cause of the phenomenon in question. What is most easily known by us is not the same as what is "most knowable by nature," the determinate cause of things. We have first a global, confused knowledge of the things around us and our first explanations are on this level. Aristotle is not arguing that there are things other than the things we first know by sensation. Rather, he is saying that what we first know about these singular things is something very general, common and confused. That is, we first know that there are mobile things, things which come into being, change ceaselessly while they are, and then pass out of being. To be changeable is something seemingly characteristic of everything in the sensible world. Thus, if we examine what is proper to them under this most universal aspect, we will be on our way towards knowledge of natural things. The next step will be to distinguish different kinds of mobile being and to study their characteristics as different, and by proceeding downwards through steps of universality, we aim to arrive at "determinate knowledge of this particular, specific mobile thing," e.g., horse.

Nothing is more important for an understanding of Aristotle than this notion of the order of procedure in the study of nature. And nothing is more commonly overlooked. In his Physics, Aristotle is concerned with examining the common characteristics of mobile being. What he discovers there should be true of every physical thing, but the Physics does not pretend to show how this kind of physical thing differs from that. For what is being sought is that which every physical thing has in common. Furthermore, it is foolish to think that Aristotle proceeds deductively from one level of universality to another, as if from the notion of "changeable being" he could infer the existence of any species of mobile being. Aristotle is the first to warn against attempting this, urging that acquaintance with nature is the only road to more determinate statements about it.

We will come back later to the way in which Aristotle's mode of procedure can be traced through his many works on nature. For the moment, let us keep in mind that the analyses of the Physics are intended to be true of every physical thing, but should not be confused with specific and proper knowledge of any physical thing. This work of Aristotle's is the first step in an orderly approach to nature: the order to be followed is the first thing Aristotle treats in the Physics and he keeps coming back to it in his other natural writings.

The Historical Background. We must here recapitulate some of the points raised in the first part of this book concerning the doctrine of Parmenides and its aftermath. Parmenides, we recall, denied the possibility of change because it seemed to involve a passage from non-being to being, from nothing to something. Discussed on this stratospheric level, his argument appears to be irrefutable. Here is being. You say that it has come to be. But from what previous state could it come? There are two possibilities: being or non-being. But if being comes from being, there seems to be no change; where beforehand there was being, there is now being. If we should say that being came from non-being, this is to say too much. Thus, change is impossible; there is only being. For somewhat the same reasons, being must be one, unique, without parts, an utterly indistinguishable sphere; for how could two beings differ? Surely they would not differ insofar as they are being; this is what they have in common; and, should we say that they differ in non-being, this is tantamount to saying there is no difference between them, that is, they are the same. Now the obvious retort to Parmenides is oblique; we see many things each of which is. Parmenides is ready for us; sensation cannot be trusted if it appears to conflict with the logic of the foregoing arguments. The student will learn to sympathize with thinkers who followed on Parmenides by exercising his own wits to find a solution or way out of the Parmenidean dilemma. These thinkers, as we have seen, attempted to devise ways of accepting both change and the denial of change. What could not change or come to be, is what truly is. Ignoring the Parmenidean strictures against multiplicity considered apart from the problem of change, the atomists and Empedocles and Anaxagoras simply posited a multiplicity of ultimate building blocks of macrocosmic entities, which building blocks were the alphabet (elements) from which the world of appearance was spelled. What can be said to come to be is that which is a conglomeration of ultimate things, the things which really are and do not themselves come to be; it follows that what comes to be cannot truly be said to be; only what has not and cannot come to be truly is.

There is no denying that this is one way out of the difficulty posed by Parmenides; our own cultural climate may lead us to find it quite attractive, for we are accustomed to think that the things of our everyday experience are, in a mild sense at least, quite different from the way they appear to be. The solid quality of our desk, for example, is misleading if we think of the swarms of electrical charges which we believe compose the desk. Its surface then must be thought of as anything but solid, since there are more interstices than "components." This should indicate why Democritus' plenum and void are looked upon as a crude but interesting premonition of later scientific explanatory elements. If we have dwelt a bit on this supposed affinity of atomist doctrine and modern physics, it is because our culture does set up a block to our reoccupying the position from which Aristotle surveyed these attempts and found them wanting. What exactly is Aristotle's viewpoint?

It will be well to recall here our earlier methodological remarks. Aristotle is attempting to begin at the beginning, at what for us at any rate is the beginning of knowledge of the physical world. This beginning cannot be equated with what we nowadays for a number of reasons find familiar. By this we mean that our ready acceptance of elements and electrical charges and so forth can blind us to the fact there it is certainly not such things as these that we first know. We can imagine Aristotle expressing it somewhate as follows. You tell me that what truly exist are things I do not directly encounter but components of the latter; the things I do directly encounter are said by you not truly to be. I protest that, if I am to have some acceptable notion of what it means for a thing to be, I must have recourse to the very things you claim are not, in the rich sense of the term. You are saying, in effect, that a tree or a horse or a man is not one in the sense of one being. I cannot accept this because it is of the unitjy of such things that I must think when I attempt to imagine the imperceptible things you assure me are really one and really are. In other words, Aristotle refuses to accent the presuppositions of earlier attempts to adjust to Parmenides. He takes seriously his initial certitudes because he sees that, by one kind of prestidigitation or another, these are assumed even when they are being called into question. Obviously, then, he is faced with the problem posed by Parmenides all over again; Aristotle will insist that a tree truly is and that it has come to be and that there are many such beings. Parmenides would reply, if the tree is a being and has come to be, it must have come either from being or non-being. Aristotle has to confront that objection head on; it is because he sees the role Parmenides' argument has played in the history of natural science, and because he feels he can meet the argument head on and answer it, that Parmenides looms rather large in the first book of the Physics, despite the fact that Aristotle's questioning of the basic assumption of natural science precludes an answer from the viewpoint of the contradictory assumption. Aristotle is quite clear on this point in Chapter Two, but he also feels justified in considering Parmenides.

We physicists, on the other hand, must take for granted that the things that exist by nature are, either all or some of them, in motion -- which is indeed made plain by induction. Moreover, no man of science is bound to solve every kind of difficulty that may be raised, but only as many as are drawn falsely from the principles of the science: it is not our business to refute those that do not arise in this way: just as it is the duty of the geometer to refute the squaring of the circle by means of segments, but it is not his duty to refute Antiphon's proof. At the same time the holders of the theory of which we are speaking do incidentally raise physical questions, though Nature is not their subject: so it will perhaps be as well to spend a few words on them, especially as the inquiry is not without scientffic interest. (185a12-20)

A careful reading of Chapters Two and Three of the first book of the Physics reveals that Aristotle's ultimate weapon is that Parmenides and Melissus use terms like "being" and "one" in such a way that they must assume a meaning for these words which can be grasped only when their referents are the very things these non-physicists wish to reject.

Dialectical Summary. In Chapters Five and Six of the first book of the Physics, Aristotle asks if there are any points on which his predecessors agree despite their many disagreements. Such efforts as this are often looked upon as attempts by Aristotle to show that his predecessors were groping towards his own view. Now this is perfectly true, though badly expressed. Aristotle is not putting forth a doctrine expressive of his personal way of looking at the world and his effort should not be construed as an attempt to show that Anaxagoras, for example, was trying in a lisping way to attain the timbre of Aristotle's voice. Aristotle is infinitely more serious than the neutralist, unengaged historian of ideas. His viewpoint is at once obvious and profound. His predecessors looked hard at the world, the same one Aristotle and you and I are confronted by, and they said a number of things about it. Some of what they said can be understood by taking into account what others had said, but finally their statements must stand the test of comparison with the world they hoped to explain. Now it is quite clearly the latter test that most interests Aristotle. Moreover, he, like most of us, is disinclined to feel that men can look at the common universe and explain it in ways which are utterly different and utterly false. It is against this background that we must read Aristotle's efforts to discern in the cacaphony of previous natural doctrines some concordant views.

Their first agreement is in their recognition that contrariety is involved in change. This is true of the Presocratics; it is true of Parmenides (in the Way of Opinion) who sees the hot (fire) and cold (earth) as principles of other things. The atomists opposed the full and empty, others spoke of the rare and dense, yet others of congregation and separation. Thus, hot comes from cold and vice versa; white comes from black and vice versa and, generally, a thing comes to be from its contrary and passes into its contrary. Changes are not capricious and their non-capriciousness is expressed by this appeal to contraries as the terms of change. This basic assumption involves another. There must be something besides the contraries, something which underlies them. To say that hot becomes cold is to say that something which is hot becomes cold, not that heat becomes its opposite.

Aristotle's conclusion is that, despite their diversities, and even when appearing to speak of only one principle, previous philosophers had all relied on two contraries and a subject of these contraries in speaking about change. For example, Anaximenes says that all things are air, but in order to explain the diversity of things, he takes air as capable of possessing two contrary states, rarefaction and condensation. The diversity of things thus comes to be looked on as forming a scale read in terms of the extreme states. None of these thinkers alluded to these assumptions but, since they all made them, it is probable that these three, two contraries and their subject, will enter into the explanation of changeable being.

Principles of Changcable Being. Turning to the elaboration of the truth of the matter in Chapter Seven, Aristotle reveals the importance of his talk about order and methodology. One need expect no mention of fire, air, earth and water. What is first presented for our consideration is something we can all be reasonably expected to understand: the change involved when a man becomes a musician. With deceptive simplicity, Aristotle observes that such a change can be expressed in three ways: (1) Man becomes musical. (2) The not-musical becomes musical. (3) The not-musical man becomes a musical man.

These three expressions of the same change indicate that Aristotle is interested in the different ways in which we express that from which a change begins. Otherwise he would have set down a fourth expression of the change. The three ways of expressing the beginning of the change are "man," "not-musical" and "not-musical man." Let us call the first two simple expressions and the third composite.

Why is it that we sometimes say "X becomes Y" and at other times "From X, Y comes to be"? The grammatical distinction seems to suggest the recognition of a real difference. We would hesitate to say, "From man, musical comes to be," whereas "From not-musical, musical comes to be" feels all right. Why? Is it not because, in the first instance, man does not cease to be when he has become musical, whereas in the second, not-musical is replaced by musical? If this is so, we can speak of things which survive the change and things which do not. Only in the first expression of the change, that is in (1), does the subject of the sentence stand for what survives the change. In (3), the composite "not-musical man," like the simple term "not-musical" of (2), does not survive the change. When we have a musical man, we no longer have a not-musical man.

In our instance of a man learning how to play the lyre, there is something which is there both before and after the change, namely the man. And, as the other two expressions of the change indicate, opposites or contraries are involved: there is a change from not possessing musical art to possessing it on the part of the man. In the first expression, consequently, although only man is mentioned, he has to be understood as not being already musical, since he would hardly be said to become what he already is.

What the analysis of this change reveals, then, is that there is a subject of the change, man, where subject is understood as what is there before and after the change occurs. Understood in the subject is the negation of that which is acquired as the result of the change, a negation opposed to the new quality, i.e. not-musical to musical. What results from the change is a composite of the subject, man, and the quality, musical. What does not survive the change is the negation of the acquired quality.

Aristotle next wants to analyse another more basic kind of change in terms of what has been clarified in the more obvious instance of a man becoming musical. In the instance already analysed, something came to be such-and-such, a man came to be musical. But what of changes where something comes to be, not such-and-such, but comes to be without qualification? For example, a tree or a man comes to be. Can we explain such changes by appeal to a subject which survives the change?

We have already insisted on the fact that Aristotle is going to take seriously the certitudes of everyday life. Before a man comes to be, he is not; before a tree comes to be, it is not. When man and tree exist, they are things in a more fundamental way than the quality musical or color or the composites musical man and green tree. A man and a tree are in themselves beings in a basic sense; they are not modifications of some basic being, nor are they accidental compounds of basic beings. In a word they are substances (Aristotle's word is ousia: being). Now this is something that we all already know; the fact is certain. But how can we understand the fact? Aristotle, recall, does not want to explain it away, but to explain it. If a man and a tree come to be as the result of a change, this suggests, on an analogy with man becoming musical, a subject of the change. But, if we posit some such subject as earth or air or fire or atoms, we would be in agreement with the Presocratics and the post-Parmenidean natural philosophers. It is a costly agreement, however, for if we appeal to such subjects as these, a tree and man would be modification of it in the same way as musical is a modication of man. We know why the post-Parminidean physicists took this route; by not claiming any substance came to be, they skirted the difficulties of the Eleatic's argument. Aristotle does not want to avoid Parmenides, however, and as a result he asserts there is a subject of unqualified chapge, a subject which he calls elsewhere prime matter.

If a tree's coming to be is a change, there must be a subject of change. "But that substances too, and anything else that can be said to be without qualification, come to be from some substratum, will appear on examination. For we find in every case something underlying from which proceeds that which comes to be; for instance, animals and plants from seed." (190b1-5) This instance may seem difficult to understand, but it is remarkably well chosen. Great oaks from little acorns grow here: From X, Y comes to be. Now if a tree is appreciably different from a musical man, its coming to be will have to be explained in an appreciably different way. Just as in "Man becomes musical" there is a subject, man, so too in "a tree comes to be." In the first case, the subject of the change is a substance and the result of the change is a new accidental determination of the substance. In the second case, the subject cannot be a substance, for then any new determination of it will be an accident, and we are taking seriously our conviction that such things as trees are substantially one. But what then are we to make of the example above, an example which can be expressed as "A seed becomes a tree." Notice that this is not on a par with "A man becomes musical" since, almost biblically, unless the seed die, the tree cannot be. Thus, "The seed becomes a tree" is much more like "The non-musical becomes musical" or, better, "The hot becomes cold."

The subject of unqualified becoming, Aristotle remarks, is known by a comparison or analogy.

The underlying nature . . . of the coming to be of substance . . . is an object of knowledge by analogy. For as the bronze is to the statue, the wood to the bed, or the matter and the formless before receiving form to anything which has form, so is the underlying nature to substance, i.e., the 'this' or existent. (191a7-12)

Notice that in this statement Aristotle is appealing to a change in the realm of art as to something readily comprehensible by us; moreover, the terms he uses, "matter" and "form," seem drawn from the realm of art. The Greek equivalents of these terms, hyle and morphe, call to mind the modification of wood by imposing a new shape or form on it. The argument from analogy, then, goes beyond the example of man becoming musical, to the imposition of a shape on wood, a form on matter. When we make a bed, we impose on lumber (which is a more primitive instance of imposing an artistic shape on natural material) a new shape or form. Let us now talk of a man's becoming musical in these terms, altering their meaning somewhat as we go. Man may now be called the matter, musical the form of the product of the change. If we are to retain these same terms in speaking of the change whereby a man comes to be. their meanings must once more change; that this extension of meaning occurs is signalized by designating matter as prime matter and the form as

substantial form. Since prime matter is not a substance in its own right, it is said to have no substantial determination of itself, and thus can only be known by comparison with the subject of accidental change in the natural order or to the subject of an artificial change. If we speak of the subject of a substantial change, however, we need not think that what is meant is that it appears as the subject of sentences which express such changes. "The seed becomes a plant" is much more like what we are apt to say but, in saying it, we are not saying that the seed persists throughout the change. If we accept the fact that trees are substantial beings, that they come from seeds, and that a subject or matter must be involved if we are to speak of change -- we would be using "change" in a Pickwickian and mysterious sense if by it we meant that seeds disappear and plants appear on the analogy of a change of scenery -- then we must inevitably be led to an ultimate subject of substantial change, itself not a substance but a component of substance. Notice that this is to explain a fact of which we are certain, not to explain it away. The determination of matter whereby a substance is constituted is called form, but unlike musical it does not make something to be such-and-such, but makes it be absolutely and in the first instance. And, of course, matter could not be determined by a form it already possessed, but only by one it did not possess. Thus in all change, whether qualified (accidental) or unqualified (substantial) there are three principles necessary: matter or subject, form or determination and the previous privation of this determination on the part of the subject.

Parmenides Confronted. The test of a solution is its ability to withstand objections, to make things clearer than rival solutions to indicate how allied problems should be dealt with. It is to the second test that Aristotle wishes to put his solution to the problem of change, for he wants to show that Parmenides got into an unnecessary difficulty, thereby leading himself and others astray. The Parmenidean problem, once more, is that if we say that something has come to be we must show that it has come either from being or non-being and this we cannot do. It is wholly typical of Aristotle to subject to analysis the troublesome sentences, (1) "Being comes from being," and (2) "Being comes from non-being." Parmenides obviously understands them in such a way that (1) could be taken to mean something like "A trained seal becomes a trained seal" where after the supposed change we end up with what we began and ought not to talk of any change having occurred. Statement (2), on the other hand, becomes something like "From absolutely nothing at all, a trained seal came to be." Now this is one way to understand (1) and (2), but it is not the only way and it is not the way we would take them if we wanted them to agree with our certitude that change is real. Aristotle suggests there is another manner of understanding the way something comes from another, just as there are several ways to understand an activity attributed to a physician. For example, in "The physician heals," and "The physician golfs," we are speaking of the physician and what he does, but in the first sentence we are speaking of him qua physician, that is, just insofar as he is a physician, whereas the second activity ascribed to him is not so ascribed just because he is a physician. So too if we say hot comes from non-hot, we need not understand our remark in the way Parmenides would understand it, nor do our words imply the further assertion that hot comes from cold. Aristotle sees Parmenides' position as a result of thinking that being comes from either privation or previous determination. For example, hot (being) comes from cold (being) or from non-hot (non-being). Now, Aristotle says, hot does comes from cold and non-hot, but neither of these is a principle of what has come to be, where by a principle of what has come to be he means what is a component of the result of the change. Only the subject (water) is this kind of subject-from-which. Let us listen to Aristotle himself on this solution.

We ourselves are in agreement with them in holding that nothing can be said without qualification to come from what is not. But nevertheless we maintain that a thing may 'come to be from what is not' -- that is, in a qualified sense. For a thing comes to be from the privation, which in its own nature is not-being -- this not surviving as a constituent of the result. Yet this causes surprise, and it is thought impossible that something should come to be in the way described from what is not -- in the same way we maintain that nothing comes to be from being, and that being does not come to be except in a qualified sense. In that way, however, it does, just as animal might come to be from animal, and an animal of a certain kind from an animal of a certain kind. Thus, suppose a dog to come to be from a horse. The dog would then, it is true, come to be from an animal (as well as a certain kind) but not as animal, for that is already there. But if anything is to become an animal not in a qualified sense, it will not be from animal: and if being, not from being -- nor from not-being either, for it has been explained that by 'from not-being' we mean from not-being qua not-being. (191b13-26)

Aristotle by identifying Parmenides' not-being with privation and his being with the previous determination of the subject, effectively does away with the old difficulty by showing that neither privation nor the previous form is that from which the result of the change comes in an unqualified sense. The from which the result of the change comes without qualification is the subject as capable of possessing the new determination. That is, water from being hot only potentially comes to be actually hot. This is why we often read that Aristotle solves the difficulty of Parmenides by introducing the distinction between act and potency. It should be said, however, that this is only half the story and that the identification of being and not-being with two of the principles necessary for any change is the solution developed in the first book of the Physics.

Nature. The term "physics" is derived from the Greek term physis which Aristotle analyses in the Metaphysics, V, 4. There he points out that the term had first meant the process of being born, then the principle of that process, and then had been extended to signify the principle of any change whatsoever. It is this third sense that is operative in the Physics and, in the second book of that work, Aristotle undertakes to define it by comparing it with art. Things, he begins, are either natural or artificial. We say that animals, their parts, plants, fire, air, earth and water exist by nature, that is, are natural products. What we mean is made explicit by contrasting such things with works of art. A pair of shoes is not a natural product. The thing that distinguishes what exists "by art" from that which exists "by nature" is that the latter has the principle of its change within itself. Nature consequently can be defined as follows: it is the principle of motion and rest in that to which it belongs primarily, per se and not accidentally. By calling nature a principle, Aristotle leaves the way open to understanding it as an active or passive principle of the change, that is nature may be a power to act or a power to be acted upon. By saying that nature is a principle of motion and rest, Aristotle is alluding to the view he does not argue for here that things have a natural place in the universe: when they are in that place they are naturally at rest. By saying that it is a principle in the moved thing, Aristotle is contrasting nature to art. By calling nature a first principle, Aristotle is suggesting that change can be called natural not necessarily with respect to a compound as such, but with reference to a component of it.

Now we have already seen that the components of natural compounds are, for Aristotle, matter and form. Thus we should expect that both these will save the definition of nature, and this is precisely what Aristotle goes on to show. The change of something may be described as natural either with respect to the matter of which it is composed or with respect to its form. To indicate what this means in a very general way, let us notice that death may be natural to man because of matter, and reasoning and immortality because of form. Aristotle gives several arguments to prove that form is more deserving of the apellation nature than is matter. The discussion of the second chapter of book two turns on the difference between physics and mathematics, a point we discussed earlier.

The effect of the opening considerations of the second book is to establish the meaning of "physical things" (ta physica) in a way that connects with the analyses of the first book. We now have a fairly clear idea of what it is of which we seek scientific knowledge, a knowledge which is had through causes.

Now that we have established these distinctions, we must proceed to consider causes, their character and number. Knowledge is the object of our inquiry, and men do not think they know a thing till they have grasped the 'why' of it (which is to grasp its primary cause). So clearly we too must do this as regards both coming to be and passing away and every kind of physical change, in order that, knowing their principles, we may try to refer to these principles each of our problems. (II, 3, 194b16-23)

This sets the stage for the analysis of causes into four types, each of which will be a principle of explanation in physics. The material cause is that out of which something is made and which remains as a component of the result. The examples are from art: bronze is the material cause of the statue. The formal cause is that which is expressed in the definition of the thing. For example, if we are asked what a statue is, we would say, not bronze, but bronze shaped in such a way. The efficient cause is the primary cause of the change; e.g. the sculptor who makes the statue. The final cause, that for the sake of which something is done, is also a cause. Why does one exercise? To be healthy. This is the end or purpose explaining why one is sweating in the gym. It can be seen that a physical thing can be explained in terms of one or all of these four causes. Moreover, each type of cause can be designated in several ways. In terms of prior and posterior (distinguished according to universality) we may designate the efficient cause of health as, respectively, the trained man or the physician. A cause may be designated accidentally as when we say Polycitus is the cause of the statue, since it happens that the sculptor is named Polycitus. Finally, causes can be either actual or potential causes of their effects. The physicist's interest in the four causes is described thus by Aristotle.

Now, the causes being four, it is the business of the physicist to know them all, and if he refers his problems back to all of them, he will assign the 'why' in the way proper to his science -- the matter, the form, the mover, 'that for the sake of which.' The last three often coincide; for the 'what' and 'that for the sake of which' are one, while the primary source of motion is the same in species as these (for man generates man) . . . (II,7,198a21-27)

The form or essence of the generated things is that for the sake of which the process took place and the moving or agent cause is of the same species as its effect in natural generation. Aristotle has much to say of finality in nature, but before looking at that doctrine, we must say something about the discussions in Chapters Four through Six on accidental causes.

Chance and Fortune. We say that some things come about by chance, and Aristotle wants to investigate our reasons for doing this to see if we are speaking of a real cause. It is important to realize that Aristotle is concerned with chance as cause, something evident in our use of the phrase "by chance." Aristotle first notes a surprising range of opinions on chance. Some deny its reality and claim that anything ascribed to chance can be ascribed to a determinate cause. Meeting an old friend does not come about by chance but because one went to the market place and ran into him. Moreover, the early natural philosophers did not list chance as a cause, though some, like Empedocles, assign things to chance as to a cause. Indeed, some who do not attribute to chance the formation of lesser entities, say that the heavenly sphere is a result of chance. Finally, there are those who believe chance to be real but mysterious, inscrutable and beyond our ken. Since some things always come about in the same way, whereas others occur in a certain fashion only for the most part, there are some rare occurences as well. It is this last class of events that we ascribe to chance. In arriving at an analysis of chance in the natural realm, Aristotle proceeds by analysing chance in human affairs, what we would call fortune or luck. Very briefly, his teaching is this. Something can come about by chance only where there is an agent acting for an end. Thus, if on the way to the store I find a ten dollar bill, I would call myself lucky, the beneficiary of good fortune. In other words, I am ascribing the finding of the money to chance. What now of the first objection Aristotle recorded? Someone might say that I am guilty of fuzziness when I ascribe such an occurrence to chance; there is a determinate cause of the event. If I had not gone to the store, I would not have found the money; since I went to the store, I found the money. This objection is extremely useful, for it forces us to ask what kind of cause of my finding the money going to the store is -- that it is the cause is evident enough. But if we observe that going to the store does not usually have as its result my finding ten dollars, we are in a position to say that this is not a determinate cause of my discovery -- a determinate cause produces its effect always or for the most part (or at least, intentionally; the pole vaulter does not always or usually surpass his previous feats, but when be does it would not be advisable to congratulate him on his luck until he has laid aside his pole). The event ascribed to chance comes about rarely, outside the intention of the agent, and is good or evil for the agent. Now the regularity in nature suggests intention; freaks of nature suggest that chance is a real cause in the natural order. The universe, then, is not a concatenation of necessary occurrences for Aristotle. There are things that come about by chance, an element of caprice and unpredictability; moreover, it would make no sense to say that obviously ordered things come about by chance, since this would mean, not that there is no purpose, but that in pursuing one purpose nature accidentally brought about another. In other words, chance in nature, as Aristotle has analysed it, makes sense only against the background of nature as purposive.

Finality. Arguments against finality seem to be as old as arguments for it and Aristotle commences his discussion of nature as purposive principle by setting down objections to this view. Why can't we say that things simply come about by necessity and, rather than say that rain falls so that the crops will grow, say it rains because vapor rises and condenses and falls as rain, with the growth of the crops as an incidental effect of this necessary chain of events? So too we need not say that some teeth are for tearing and others for chewing, but that, simply given the teeth we have, it happens we find them useful for various purposes of ours. Aristotle's rejection of these objections are straightforward. Why should we ascribe to chance what comes about usually or normally? "If then, it is agreed that things are either the result of coincidence or for an end, and these cannot be the result of coincidence of chance, it follows that they must be for an end." (II, 8, 199a3-5) This view that nature acts for an end suggests the kind of necessity we may expect in our explanations of natural events.

But in things which come to be for an end, the reverse is true. If the end is to exist or does exist, that also which precedes it will exist or does exist; otherwise just as there, if the conclusion is not true, the premiss will not be true, so here the end or 'that for the sake of which' will not exist. . . If then there is to be a house, such-and-such things must be made or be there already or exist, or generally the matter relative to the end, bricks and stones if it is a house. But the end is not due to these except as the matter, nor will it come to exist because of them. (II, 9, 200a19-27)

Motion. Having defined nature as a principle of motion, Aristotle must determine what motion is if he is to have a proper understanding of the subject of physics. The discussion of motion will carry him on to allied subjects: infinity, place, void, time. We shall give a brief exposition of what Aristotle has to say concerning motion and then indicate his doctrine on the allied notions.

Motion is defined by Aristotle as the act of what exists in potency insofar as it is in potency. To understand this definition, we must make a threefold division of things into those which are wholly in act, those which are only potentially, and those which are midway between these extreme conditions. What is only potentially is not in movement; e.g., the seated man is standing only potentially. So too what is wholly in act is not in motion; e.g. the man, having stood up, is actually standing and that's that. The act of getting up out of the chair is motion and it is identified by contrast with the extreme states of potency alone and act alone. It is an imperfect act: one who is getting up is not wholly in act, i.e., not actually standing, nor wholly in potency, that is simply seated, but somewhere in between. Motion, therefore is not the potency of something existing in potency nor the act of something existing in act, but the act of something existing in potency just as such, where "just as such" indicates the relation of the imperfect act to further act. The thing existing in potency alone, e.g., the man seated, can be seen as in potency to two acts: the imperfect act which is motion and the perfect act which is the term of the motion, standing erect.

Related Notions. Since motion involves the continuum and this is said to be infinite, Aristotle goes on to define infinity. "A quantity is infinite if it is such that we can always take a part outside what has been already taken." (III,6,207a7-8) Infinity is always potential, it is that which is always further divisible. Aristotle argues against the possibility of an actual infinite. The physicist must define place as well, if only because locomotion, change of place, is the most general and common kind of motion. Place is the innermost motionless boundary of the container (IV,4,212a20-1) As to the void, Aristotle rejects it. Time he defines as the number of motion with respect to the before and after. (IV, 11, 219b1-2)

In the fifth book of the Physics, Aristotle divides motion into its species, locomotion, alteration, augmentation and decrease, motions in the categories of place, quality and quantity, respectively. He then discusses the unity and opposition of motions. In the sixth book, he discusses the quantitative parts of motion.

In the last two books of the Physics, Aristotle discusses the Prime Mover. That such a mover exists is proved by appeal to two truths: whatever is moved is moved by another and there cannot be an infinite series of moved and moving things. Thus there must be a first unmoved mover if motion is to be explained; Aristotle proceeds here on the assumption that motion is eternal and has not had a beginning. The Prime Mover is shown to be without parts or magnitude. Having arrived at an entity which is immobile and incorporeal, Aristotle has encountered a being which does not as such fall under the scope of natural science. As we will see, it is this proof that something immaterial and immobile exists that permits Aristotle to say that "being" need not be taken to mean mobile being alone; in other words, there is a possibility for another science whose subject is being as being. That science is First Philosophy, what has come to be called Metaphysics, and in discussing it, we will examine Aristotle's notion of a Prime Mover. Treatises Consequent on the Physics. We saw earlier Aristotle's concern for orderly procedure in natural science. This attention to method is not confined to the materials of one work, but applies as well to the relation of the various works to one another. In this wider perspective, the Physics presents doctrine presupposed in the other natural works and is thus prior to all the rest. In this introductory work we find a general analysis of motion, a comparison of types of motion, and so forth. It is in terms of types of motion that the later works can be seen to be divided, and since there is an order of priority and posteriority among the species of motion, there is also an order among the works concerned with them. It has been proved in the Physics that local motion is the first and most common motion; thus, in On the Heavens both heavenly and terrestial bodies are treated insofar as they are subject to local motion. Subsequent motions, that according to quality and that according to quantity, are thought not to be common to every natural thing: alteration, taken as ordered to generation, is confined to terrestial things and On Generation and Corruption is concerned with such things from that viewpoint. The discussion of the transmutation of the elements (fire, air, earth and water) is continued in the Meteorology. Augmentation and decrease, looked upon as following the taking of nourishment, lead to the discussion of living beings, a discussion commenced in On the Soul and carried on in On Sense and the Object of Sense, On Memory and Reminiscence and in the many works on animals. The whole sweep of Aristotelian natural doctrine thus appears as a movement from general truths which cover natural things indiscriminately to determinate, concrete statements about natural things in their specificity. We must here satisfy ourselves with a few remarks on his general treatise on the soul.

The Soul. Aristotle begins his discussion of the nature and properties of the soul by indicating the desirability and value of possessing such knowledge as well as the difficulties which face one who would ask of soul, what is it? There is no one method to be followed when one is seeking knowledge of essence as there is one method for demonstrating properties. What we must ask is what genus contains soul; whether soul is a substance, quality or something quantitative, or something else; further, we must ask if it is something potential or actual. Moreover, we must be careful to ask whether soul can be defined in general without regard to its species, or whether we must from the outset seek the definition of a determinate type of soul.

We must be careful not to ignore the question whether soul can be defined in a single unambiguous formula, as is the case with animal, or whether we must not give a separate formula for each sort of it, as we do for horse, dog, man, god (in the latter case the 'universal' animal -- and so too every other common predicate -- being treated either as nothing at all or as a later product). (I,1,402b5-9)

Again, if there are parts of the soul, should these be considered before or after soul itself? A question also arises concerning the mode of defining the passions or affections of soul, since it seems necessary to include the body in such definitions. "That is precisely why the study of the soul must fall within the science of nature, at least so far as in its affections it manifests this double character." (403a27-8) Before turning to his own answers to these and allied questions, Aristotle polls his predecessors to see what they had to say on the subject of soul, a survey that occupies the remainder of the first book.

When he turns to the task of defining the soul in the second book, Aristotle begins with a number of divisions. First, he points out that there is a threefold sense of "substance:" matter, form, and the compound of the two. Furthermore, matter is potentiality, form actuality. Finally, actuality is of two sorts, exemplified by the possession of knowledge and the use of knowledge. Now the most obvious instances of substance are natural bodies and of these some have life, others do not. A sign that a body is living is self-nutrition or growth. Thus, living natural bodies are substances in the sense of compounds of matter and form.

But since it is also body of such and such a kind, viz. having life, the body cannot be soul; the body is the subject or matter, not what is attributed to it. Hence the soul must be a substance in the sense of the form of a natural body having life potentially within it. But substance is actually. and thus soul is the actuality of a body as above characterized. Now the word actuality has two senses corresponding respectively to the possession of knowledge and the actual exercise of knowledge. It is obvious that the soul is actuality in the first sense, viz. that of knowledge as possessed, for both sleeping and waking presuppose the existence of the soul, and of these waking corresponds to actual knowing, sleeping to knowledge possessed but not employed, and, in the history of the individual, knowledge comes before its employment or exercise. That is why the soul is the first grade of actuality of a natural body having life potentially within it. (II,1,412a16-28)

The soul is the substantial form of the living body; for this reason, body is described as that which has life potentially. The genesis of the living thing is a substantial generation and cannot be the addition of life to an already constituted body as if this were the addition of an accidental determination. Soul is the first actuality of living body, determining it as to what it is.

Aristotle goes on to say that the body which has life potentially is an organic body; a diversity of parts is required for the diversity of vital functions.

Aristotle's procedure indicates that he is in effect answering several of the questions he posed at the outset of the first book. The soul is substance in the sense of form furthermore, it is something actual, indeed the first act of living body. To the question as to whether soul in general can first be defined, Aristotle is answering in the affirmative. "We have now given an answer to the question, What is soul? -- and answer which applies to it in its full extent." (412b10) Finally, the soul is considered before its parts.

Having given a definition of the soul, Aristotle wants to explain it and to do this he returns to his distinction of natural bodies into those which are living and those which are not. How do we come to say that some bodies are living? Obviously, because they manifest life. but this is done in a variety of ways, and if any of them is present it suffices to say that a body is alive. "Living, that is, may mean thinking or sensation or local movement and rest, or movement in the sense of nutrition, decay and growth." (413a23-5) The soul is that whereby the living thing performs any and all of these operations, but their diversity suggests parts or faculties or powers of soul and these faculties are related as prior to posterior. Thus, self-nutrition can not only be considered apart from other powers or faculties, it can also exist apart in the sense that some living things possess only this grade of life. When living things also possess the power of sensation, we say that they are animals, and among the faculties of sense, touch is the most basic, since any animal must have this at least. Thus, self-nutrition enables us to group plants and animals, possession of touch enables us to group all animals together. The power of thinking sets the human soul apart from other animal souls. There are three species of soul, then, the plant, the animal and the human, and of each of them the definition of soul given at the outset can be predicated univocally. Nevertheless, when we turn to the species of the soul, we notice that there is a certain order among them; the human soul has the capacities of the animal soul and more besides; the animal soul has the capacities of the plant soul and more besides. The most basic type of soul, consequently, is the plant soul. Aristotle likens the relations among the species of soul to those obtaining among the species of figure: the triangle is contained in the square, etc. (414b20 ff.)

The remainder of the second book is occupied with the discussion of the nutritive power and the external senses, sight, hearing, smell, taste and touch. In the third book, Aristotle speaks of internal senses. The common sense is that which accounts for sensible awareness of the differences among the objects of external sense. As St. Thomas puts it: "We know the difference between white and sweet, not only with respect to what each is, for this is done by intellect, but also with respect to a diverse immutation of sense and this can only be done by sense." (In III De Anima, 1.3, n. 601) Imagination is the internal sense whereby we have sensory awareness of objects no longer present to the external senses. The highpoint of On the Soul is reached in the discussion of that faculty with which the soul knows and thinks. Aristotle first compares intellection with sensation and then makes this important statement.

Thus that in the soul which is called mind (by mind I mean that whereby the soul thinks and judges) is, before it thinks, not actually any real thing. For this reason it cannot reasonably be regarded as blended with the body: if so, it would acquire some quality, e.g., warmth or cold, or even have an organ like the sensitive faculty: as it is, it has none. It was a good idea to call the soul 'the place of forms' though (1) this description holds only of the intellective soul, and (2) even this is the forms only potentially, not actually. (III,4,429a22-9)

An indication of the difference between sense and intellect is found in the fact that our ability to see can be impaired by an object too bright whereas when mind concentrates on what is more knowable it is afterwards more able to think of objects less intelligible: "the reason is that while the faculty of sensation is dependent upon the body, mind is separable from it." (429b4-5) It is the realization that intellectual activity is independent of body that leads Aristotle to the assertion that the intellective soul is immortal and eternal.

And in fact mind as we have described it is what it is by virtue of becoming all things, while there is another which is what it is by virtue of making all things: this is a sort of positive state like light; for in a sense light makes potential colors into actual colors. Mind in this sense of it is separable, impassible, unmixed, since it is in its essential nature activity . . . Actual knowledge is identical with its object: in the individual, potential knowledge is in time prior to actual knowledge, but in the universe as a whole it is not prior even in time. Mind is not at one time knowing and at another not. When mind is set free from its present conditions it appears as just what it is and nothing more: this alone is immortal and eternal . . . (430a14ff.)

Aristotle speaks of two intellectual faculties: the agent, here compared to light, and the passive, that which actually becomes what it knows. Since the activity of each is separable, not involving the body, the soul of which they are faculties survives death.

This passage is extemely difficult and the interpretation we have given of it would be rather generally contested. In the Middle Ages Aristotle's doctrine of a passive and agent intellect, the separability of each, and whether they are faculties of the human soul will be points of great contention. Whether one accepts or rejects the view that Aristotle demonstrates the immortality of the soul in the third book of On the Soul, it is clear that neither in that work nor in any other treatise does he undertake to discuss the status of the human soul as separated from the body.

In Chapter Six of the third book, Aristotle establishes the two-fold operation of intellect he had presupposed in On Interpretation. Mention must be made of the famous Aristotelian remark that the soul is in a way all things, since existing things are either objects of sensation or thought. He stresses the dependence of intellection on sensation, and teaches that intellectual activity always involves concomitant imaginative activity.

If it is accepted that Aristotle proves in On the Soul that the human soul does not perish at death, we find two instances in natural philosophy where thought is led to the reasoned realisation that there is an existent separable from matter and motion: the Prime Mover and the intellectual soul after death. It is against the background of these discoveries that Aristotle is able to go on to speak of a speculative science which has as its subject being as being, a phrase that suggests that his interest is no longer confined to being as mobile. Of course, it would make little sense to speak of being as being if this were tantamount to being as mobile: there would be no distinct science of it. Before turning to an examination of Aristotle's doctrine contained in the books of the Metaphysics, we must first consider his practical philosophy.