Amongst the special sciences treated by Aristotle, the Physics is contained in a whole series of physical treatises, which form a tolerably complete system of what constitutes the Philosophy of Nature in its whole extent. We shall try to give their general plan. Aristotle’s first work is his Treatise, in eight books, on Physics, or on the Principles (φυσικὴ ἀκρόασις ἢ περὶ ἀρχῶν). In this he deals, as is fitting, with the doctrine of the Notion of nature generally, with movement, and with space and time. The first manifestation of absolute substance is movement, and its moments are space and time; this conception of its manifestation is the universal, which realizes itself first in the corporeal world, passing into the principle of separation. Aristotle’s Physics is what for present physicists would, properly speaking, be the Metaphysics of Nature; for our physicists only say what they have seen, what delicate and excellent instruments they have made, and not what they have thought. This first work by Aristotle is followed by his treatises concerning the Heavens, which deal with the nature of body and the first real bodies, the earth and heavenly bodies in general, as also with the general abstract relation of bodies to one another through mechanical weight and lightness, or what we should call attraction; and finally, with the determination of abstract real bodies or elements. Then follow the treatises on Production and Destruction, the physical process of change, while formerly the ideal process of movement was considered. Besides the physical elements, moments which are only posited in process, as such, now enter in: for instance, warmth, cold, &c. Those elements are the real existent facts, while these determinations are the moments of becoming or of passing away, which exist only in movement. Then comes the Meteorology; it represents the universal physical process in its most real forms. Here particular determinations appear, such as rain, the saltness of the sea, clouds, dew, hail, snow, hoar-frost, winds, rainbows, boiling, cooking, roasting, colours, &c. On certain matters, such as the colours, Aristotle wrote particular treatises. Nothing is forgotten, and yet the presentation is, on the whole, empiric. The book On the Universe, which forms the conclusion, is said not to be genuine; it is a separate dissertation, addressed to Alexander, which contains in part the doctrine of the universality of things, a doctrine found already in the other treatises; hence this book does not belong to this series.
From this point Aristotle proceeds to organic nature, and here his works not only contain a natural history, but also a physiology and anatomy. To the anatomy pertain his works on the Locomotion of Animals, and on the Parts of Animals. He deals with physiology in the works on the Generation of Animals, on the common Movement of Animals; and then he comes to the distinction between Youth and Age, Sleeping and Waking, and treats of Breathing, Dreaming, the Shortness and Length of Life, &c., all of which he deals with partly in an empiric, and partly in a more speculative manner. Finally, there comes the History of Animals, not merely as a history of Nature, but also as the history of the animal in its entirety—what we may call a kind of physiologico-anatomical anatomy. There is likewise a botanical work On Plants (περὶ φυτῶν) which is ascribed to him. Thus we here find natural philosophy in the whole extent of its outward content.
As regards this plan, there is no question that this is not the necessary order in which natural philosophy or physics must be treated. It is long since physics adopted in its conception the form and tendency derived from Aristotle, of deducing the parts of the science from the whole; and thus even what is not speculative still retains this connection as far as outward order goes. This is plainly to be preferred to the arrangement in our modern text-books, which is a wholly irrational succession of doctrines accidentally put together, and is undoubtedly more suitable to that method of contemplating nature, which grasps the sensuous manifestation of nature quite irrespective of sense or reason. Physics before this contained some metaphysics, but the experience which was met with in endeavouring unsuccessfully to work it out, determined the physicists, so far as possible, to keep it at a distance, and to devote their attention to what they call experience, for they think that here they come across genuine truth, unspoiled by thought, fresh from the hand of nature; it is in their hands and before their faces. They can certainly not dispense with the Notion, but through a kind of tacit agreement they allow certain conceptions, such as forces, subsistence in parts, &c., to be valid, and make use of these without in the least knowing whether they have truth and how they have truth. But in regard to the content they express no better the truth of things, but only the sensuous manifestation. Aristotle and the ancients understand by physics, on the other hand, the comprehension of nature—the universal; and for this reason Aristotle also calls it the doctrine of principles. For in the manifestation of nature this distinction between the principle and what follows it, manifestation, really commences, and it is abrogated only in genuine speculation. Yet if, on the one hand, what is physical in Aristotle is mainly philosophic and not experimental, he yet proceeded in his Physics in what may be called an empiric way. Thus, as it has been already remarked of the Aristotelian philosophy in general that the different parts fall into a series of independently determined conceptions, so we find that this is the case here also; hence an account can only be given of a part of them. One part is not universal enough to embrace the other part, for each is independent. But that which follows, and which has in great measure reference to what is individual, no longer comes under the dominion of the Notion, but becomes a superficial suggestion of reasons, and an explanation from the proximate causes, such as we find in our physics.
In regard to the general conception of nature, we must say that Aristotle represents it in the highest and truest manner. For in the Idea of nature Aristotle (Phys. II. 8) really relies on two determinations: the conception of end and the conception of necessity. Aristotle at once grasps the whole matter in its principles, and this constitutes the old contradiction and divergence of view existing between necessity (causæ efficientes) and end (causæ finales), which we have inherited. The first mode of consideration is that in accordance with external necessity, which is the same as chance—the conception that all that pertains to nature is determined from without by means of natural causes. The other mode of consideration is the teleological, but conformity to end is either inward or outward, and in the more recent culture the latter has long retained the supremacy. Thus men vibrate in their opinion between these two points of view, seek external causes, and war against the form of an external teleology which places the end outside of nature. These determinations were known to Aristotle, and he thoroughly investigates them and considers what they are and mean. Aristotle’s conception of nature is, however, nobler than that of to-day, for with him the principal point is the determination of end as the inward determinateness of natural things. Thus he comprehended nature as life, i.e. as that which has its end within itself, is unity with itself, which does not pass into another, but, through this principle of activity, determines changes in conformity with its own content, and in this way maintains itself therein. In this doctrine Aristotle has before his eyes the inward immanent end, to which he considers necessity an external condition. Thus, on the one hand, Aristotle determines nature as the final cause, which is to be distinguished from what is luck or chance; it is thus opposed by him to what is necessary, which it also contains within itself; and then he considers how necessity is present in natural things. In nature we usually think of necessity first, and understand as the essentially natural that which is not determined through end. For long men thought that they determined nature both philosophically and truly in limiting it to necessity. But the aspect of nature has had a stigma removed from it, because, by means of its conformity to the end in view, it is elevated above the commonplace. The two moments which we have considered in substance, the active form and matter, correspond with these two determinations.
We must first consider the conception of adaptation to end as the ideal moment in substance. Aristotle begins (Phys. II. 8) with the fact that the natural is the self-maintaining, all that is difficult is its comprehension. “The first cause of perplexity is, what hinders nature from not operating for the sake of an end, and because it is better so to operate, but” being, for example, “like Jupiter, who rains, not that the corn may grow, but from necessity. The vapour driven upwards cools, and the water resulting from this cooling falls as rain, and it happens that the corn is thereby made to grow. In like manner, if the corn of any one is destroyed, it does not rain for the sake of this destruction, but this is an accidental circumstance.” That is to say, there is a necessary connection which, however, is an external relation, and this is the contingency of the cause as well as of the effect. “But if this be so,” Aristotle asks, “what hinders us from assuming that what appears as parts” (the parts of an animal, for instance) “may thus subsist in nature, too, as contingent? That, for example, the front teeth are sharp and adapted for dividing, and that the back teeth, on the contrary, are broad and adapted for grinding the food in pieces, may be an accidental circumstance, not necessarily brought about for these particular ends. And the same is true with respect to the other parts of the body which appear to be adapted for some end; therefore those living things in which all was accidentally constituted as if for some end, are now, having once been so existent, preserved, although originally they had arisen by chance, in accordance with external necessity.” Aristotle adds that Empedocles especially had these reflections, and represented the first beginnings of things as a world composed of all sorts of monstrosities, such as bulls with human heads; such, however, could not continue to subsist, but disappeared because they were not originally constituted so that they should endure; and this went on until what was in conformity with purpose came together. Without going back to the fabulous monstrosities of the ancients, we likewise know of a number of animal tribes which have died out, just because they could not preserve the race. Thus we also require to use the expression development (an unthinking evolution), in our present-day natural philosophy. The conception that the first productions were, so to speak, attempts, of which those which did not show themselves to be suitable could not endure, is easily arrived at by natural philosophy. But nature, as entelecheia or realization, is what brings forth itself. Aristotle hence replies: “It is impossible to believe this. For what is produced in accordance with nature is always, or at least for the most part, produced” (external universality as the constant recurrence of what has passed away), “but this is not so with what happens through fortune or through chance. That in which there is an end (τέλος), equally in its character as something which precedes and as something which follows, is made into end; as therefore a thing is made, so is its nature, and as is its nature, so is it made; it exists therefore for the sake of this.” The meaning of nature is that as something is, it was in the beginning; it means this inward universality and adaptation to end that realizes itself; and thus cause and effect are identical, since all individual parts are related to this unity of end. “He who assumes contingent and accidental forms, subverts, on the other hand, both nature itself and that which subsists from nature, for that subsists from nature which has a principle within itself, by whose means, and being continually moved, it attains its end.” In this expression of Aristotle’s we now find the whole of the true profound Notion of life, which must be considered as an end in itself—a self-identity that independently impels itself on, and in its manifestation remains identical with its Notion: thus it is the self-effectuating Idea. Leaves, blossoms, roots thus bring the plant into evidence and go back into it; and that which they bring to pass is already present in the seed from which they took their origin. The chemical product, on the contrary, does not appear to have itself similarly present, for from acid and base a third appears to come forth; but here, likewise, the essence of both these sides, their relationship, is already present, though it is there mere potentiality, as it is in the product merely a thing. But the self-maintaining activity of life really brings forth this unity in all relationships. What has here been said is already contained in that which was asserted by those who do not represent nature in this way, but say, “that which is constituted as though it were constituted for an end, will endure.” For this is the self-productive action of nature. In the modern way of looking at life this conception becomes lost in two different ways; either through a mechanical philosophy, in which we always find as principle pressure, impulse, chemical relationships and forces, or external relations generally—which certainly seem to be inherent in nature, but not to proceed from the nature of the body, seeing that they are an added, foreign appendage, such as colour in a fluid; or else theological physics maintain the thoughts of an understanding outside of the world to be the causes. In the Kantian philosophy we for the first time have that conception once more awakened in us, for organic nature at least; life has there been made an end to itself. In Kant this indeed had only the subjective form which constitutes the essence of the Kantian philosophy, in which it seems as though life were only so determined by reason of our subjective reasoning; but still the whole truth is there contained that the organic creation is the self-maintaining. The fact that most recent times have brought back the rational view of the matter into our remembrance, is thus none else than a justification of the Aristotelian Idea.
Aristotle also speaks of the end which is represented by organic nature in itself, in relation to the means, of which he says (Phys. II. 8): “If the swallow builds her nest, and the spider spreads her web, and trees root themselves in the earth, for the sake of nutriment, there is present in them a self-maintaining cause of this kind, or an end.” For this instinctive action exhibits an operation of self-preservation, as a means whereby natural existence becomes shut up and reflected into itself. Aristotle then brings what is here said into relation with general conceptions which he had earlier maintained (p. 138): “Since nature is twofold as matter and form, but since the latter is end, and the rest are on account of the end, this is final cause.” For the active form has a content, which, as content of potentiality, contains the means which make their appearance as adapted for an end, i.e. as moments established through the determinate Notion. However much we may, in the modern way of regarding things, struggle against the idea of an immanent end, from reluctance to accept it, we must, in the case of animals and plants, acknowledge such a conception, always re-establishing itself in another. For example, because the animal lives in water or in air, it is so constructed that it can maintain its existence in air or water; thus it requires water to explain the gills of fishes; and, on the other hand, because the animal is so constructed, it lives in water. This activity in transformation thus does not depend in a contingent way on life; it is aroused through the outward powers, but only in as far as conformity with the soul of the animal permits.
In passing, Aristotle here (Phys. II. 8) makes a comparison between nature and art, which also connects what results with what goes before, in accordance with ends. “Nature may commit an error as well as art; for as a grammarian sometimes makes a mistake in writing, and a physician in mixing a medicinal draught, nature, too, sometimes does not attain its ends. Its errors are monstrosities and deformities, which, however, are only the errors of that which operates for an end. In the production of animals and plants, an animal is not at first produced, but the seed, and even in it corruption is possible.” For the seed is the mean, as being the not as yet established, independent, indifferent, free actuality. In this comparison of nature with art we ordinarily have before us the external adaptation to end, the teleological point of view, the making for definite ends. And Aristotle declaims against this, while he remarks that if nature is activity for a certain end, or if it is the implicitly universal, “it is absurd to deny that action is in conformity with end, because that which moves cannot be seen to have deliberated and considered.” The understanding comes forward with the determination of this end, and with its instruments and tools, to operate on matter, and we carry this conception of an external teleology over into nature. “But art also,” says Aristotle, “does not deliberate. If the form of a ship were the particular inward principle of the timber, it would act as nature prompted. The action of nature is very similar to the exercise of the art whereby anyone heals himself.” Through an inward instinct the animal avoids what is evil, and does what is good for him; health is thus essentially present to him, not as a conscious end, but as an understanding which accomplishes its ends without conscious thought.
As Aristotle has hitherto combated an external teleology, he directs another equally applicable remark (Phys. II. 9) against merely external necessity, and thus we come to the other side, or to how necessity exists in nature. He says in this regard: “Men fancy that necessity exists in this way in generation, just as if it were thought that a house existed from necessity, because heavy things were naturally carried downwards, and light things upwards, and that, therefore, the stones and foundation, on account of their weight, were under the earth, and the earth, because it was lighter, was further up, and the wood in the highest place because it is the lightest.” But Aristotle thus explains the facts of the case. “The house is certainly not made without these materials, but not on account of, or through them (unless the material so demands), but it is made for the sake of concealing and preserving certain things. The same takes place in everything which has an end in itself; for it is not without that which is necessary to its nature, and yet it is not on account of this, unless the matter so demands, but on account of an end. Hence the necessary is from hypothesis only, and not as end, for necessity is in matter, but end is in reason (λόγῳ). Thus it is clear that matter and its movement are necessity in natural things; both have to be set forth as principle, but end is the higher principle.” It undoubtedly requires necessity, but it retains it in its own power, does not allow it to give vent to itself, but controls external necessity. The principle of matter is thus turned into the truly active ground of end, which means the overthrow of necessity, so that that which is natural shall maintain itself in the end. Necessity is the objective manifestation of the action of its moments as separated, just as in chemistry the essential reality of both the extremes—the base and the acid—is the necessity of their relation.
This is the main conception of Aristotelian Physics. Its further development concerns the conceptions of the different objects of nature, a material for speculative philosophy which we have spoken of above (pp. 153-155), and regarding which Aristotle puts before us reflections both difficult and profound. Thus he at first (Phys. III. 1-3) proceeds from this point to movement (κίνησις), and says that it is essential that a philosophy of nature should speak of it, but that it is difficult to grasp; in fact, it is one of the most difficult conceptions. Aristotle thus sets to work to understand movement in general, not merely in space and time, but also in its reality; and in this sense he calls it “the activity of an existent thing which is in capacity, so far as it is in capacity.” He explains this thus: “Brass is in capacity a statue; yet the motion to become a statue is not a motion of the brass so far as it is brass, but a motion of itself, as the capacity to become a statue. Hence this activity is an imperfect one (ἀτελής),” i.e. it has not its end within itself, “for mere capacity, whose activity is movement, is imperfect.” The absolute substance, the moving immovable, the existent ground of heaven which we saw as end, is, on the contrary, both activity itself and the content and object of activity. But Aristotle distinguishes from this what falls under the form of this opposition, “That moving is also moved which has movement as a capacity, and whose immobility is rest. That in which movement is present has immobility as rest; for activity in rest, as such, is movement.” That is to say, rest is capacity for motion. “Hence movement is the activity of that which is movable (κινητοῦ),[93] so far as it is movable; but this happens from the contact of that which is motive (κινητικοῦ), so that at the same time it is posited as passive likewise. But that which moves always introduces a certain form or end (εἶδος), either this particular thing (τόδε), or a quality or a quantity, which is the principle and cause of the motion when it moves; thus man, as he is in energy, makes man from man as he is in capacity. Thus, too, it is evident that movement is in the movable thing: for it is the activity of this, and is derived from that which is motive. The activity of that which is motive is likewise not different, for both are necessarily activity. It is motive because it has the capacity for being so; but it causes motion because it energizes. But it is the energetic of the moveable (ἔστιν ἐνεργητικὸν τοῦ κινετοῦ), so that there is one energy of both; just as the relation between one and two is the same as that between two and one, and there also is the same relation between acclivity and declivity, so the way from Thebes to Athens is the same as from Athens to Thebes. Activity and passivity are not originally (κυρίως) the same, but in what they are inherent, in motion, they are the same. In Being (τῷ εἶναι) they are identical, but activity, in so far as it is activity of this in this” (what is moved), “and the activity of this from this” (what moves), “is different as regards its conception (τῷ λόγῳ).” Aristotle subsequently deals with the infinite (Phys. III. 4-8).
“In like manner it is necessary,” says Aristotle (Phys. IV. 1-5), “that the natural philosopher should consider the subject of place (τόπος).” Here come various definitions and determinations under which space generally and particular space or place appear. “Is place a body? It cannot be a body, for then there would be in one and the same, two bodies. Again, if it is the place and receptacle (χώρα) of this body, it is evident that it is so also of the superficies and the remaining boundaries; but the same reasoning applies to these, for where the superficies of water were before, there will now be the superficies of air,” and thus the places of both superficies would be in one. “But in truth there is no difference between the point and the place of the point, so that if place is not different from the other forms of limitation, neither is it something outside of them. It is not an element, and neither consists of corporeal nor of incorporeal elements, for it possesses magnitude, but not body. The elements of bodies are, however, themselves bodies, and no magnitude is produced from intelligible elements. Place is not the material of things, for nothing consists of it—neither the form, nor the Notion, nor the end, nor the moving cause; and yet it is something.” Aristotle now determines place as the first unmoved limit of that which is the comprehending: it comprehends the body whose place it is, and has nothing of the thing in itself; yet it co-exists with the thing, because the limits and the limited co-exist. The uttermost ends of what comprehends and of what is comprehended are identical, for both are bounds; but they are not bounds of the same, for form is the boundary of the thing, place is that of the embracing body. Place, as the comprehending, remains unchangeably passive while the thing which is moved is moved away; from which we see that place must be separable from the thing. Or place, according to Aristotle, is the boundary, the negation of a body, the assertion of difference, of discretion; but it likewise does not merely belong to this body, but also to that which comprehends. There is thus no difference at all, but unchangeable continuity. “Place is neither the universal (κοινός) in which all bodies are” (heaven), “nor the particular (ἴδιος), in which they are as the first (πρώτῳ).” Aristotle also speaks of above and below in space, in relation to heaven as that which contains, and earth as what is beneath. “That body, outside of which is a comprehending body, is in space. But the whole heavens are not anywhere, since no body comprehends them. Outside the universe nothing is, and hence everything is in the heavens, for the heavens are the whole. Place, however, is not the heavens, but its external quiescent boundary which touches the body moved. Hence the earth is in water, water in air, air in ether, but ether in the heavens.”