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.