IV.

In mastering Aristotle’s cosmology, we have gained the key to his entire method of systematisation. Henceforth, the Stagirite has no secrets from us. Where we were formerly content to show that he erred, we can now show why he erred; by generalising his principles of arrangement, we can exhibit them still more clearly in their conflict with modern thought. The method, then, pursued by Aristotle is to divide his subject into two more or less unequal masses, one of which is supposed to be governed by necessary principles, admitting of certain demonstration; while the other is irregular, and can only be studied according to the rules of probable evidence. The parts of the one are homogeneous and concentrically disposed, the movements of each being controlled by that immediately outside and above it. The parts of the other are heterogeneous and distributed among a number of antithetical pairs, between whose members there is, or ought to be, a general equilibrium preserved, the whole system having a common centre which either oscillates from one extreme to another, or holds the balance between them. The second system is enclosed within the first, and is altogether dependent on it for the impulses determining its processes of metamorphosis and equilibration. Where the internal adjustments of a system to itself or of one system to the other are not consciously made, Aristotle calls them Nature. They are always adapted to secure its everlasting continuance either in an individual or a specific form. Actuality belongs more particularly to the first sphere, and possibility to the second, but both are, to a certain extent, represented in each.

We have already seen how this fundamental division is applied to the universe as a whole. But our philosopher is not content with classifying the phenomena as he finds them; he attempts to demonstrate the necessity of their dual existence; and in so doing is guilty of something very like a vicious circle. For, after proving from the terrestrial movements that there must be an eternal movement to keep them going, he now assumes the revolving aether, and argues that there must be a motionless solid centre for it to revolve round, although a geometrical axis would have served the purpose equally well. By a still more palpable fallacy, he proceeds to show that a body whose tendency is towards the centre, must, in the nature of things, be opposed by another body whose tendency is towards the circumference. In order to fill up the interval created by this opposition, two intermediate bodies are required, and thus we get the four elements—earth, water, air, and fire. These, again, are resolved into the antithetical couples, dry and wet, hot and cold, the possible combinations of which, by twos, give us the four elements once more. Earth is dry and cold, water cold and wet, air wet and hot, fire hot and dry; each adjacent pair having a quality in common, and each element being characterized by the excess of a particular quality; earth is especially dry, water cold, air wet, and fire hot. The common centre of each antithesis is what Aristotle calls the First Matter, the mere abstract unformed possibility of existence. This matter always combines two qualities, and has the power of oscillating from one quality to another, but it cannot, as a rule, simultaneously exchange both for their opposites. Earth may pass into water, exchanging dry for wet, but not so readily into air, which would necessitate a double exchange at the same moment.

Those who will may see in all this an anticipation of chemical substitution and double decomposition. We can assure them that it will be by no means the most absurd parallel discovered between ancient and modern ideas. It is possible, however, to trace a more real connexion between the Aristotelian physics and mediaeval thought. We do not of course mean the scholastic philosophy, for there never was the slightest doubt as to its derivation; we allude to the alchemy and astrology which did duty for positive science during so many centuries, and even overlapped it down to the time of Newton, himself an ardent alchemist. The superstitions of astrology originated independently of the peripatetic system, and probably long before it, but they were likely to be encouraged by it instead of being repressed, as they would have been by a less anthropomorphic philosophy. Aristotle himself, as we have seen, limited the action of the heavens on the sublunary sphere to their heating power; but, by crediting them with an immortal reason and the pursuit of ends unknown to us, he opened a wide field for conjecture as to what those ends were, and how they could be ascertained. That the stars and planets were always thinking and acting, but never about our affairs, was not a notion likely to be permanently accepted. Neither was it easy to believe that their various configurations, movements, and names (the last probably revealed by themselves) were entirely without significance. From such considerations to the casting of horoscopes is not a far remove. The Aristotelian chemistry would still more readily lend itself to the purposes of alchemy. If Nature is one vast process of transmutation, then particular bodies, such as the metals, not only may, but must be convertible into one another. And even those who rejected Aristotle’s logic with scorn still clung to his natural philosophy when it flattered their hopes of gain. Bacon kept the theory of substantial forms. His originality consisted in looking for a method by which any form, or assemblage of forms might be superinduced at pleasure on the underlying matter. The real development of knowledge pursued a far different course. The great discoverers of the sixteenth and seventeenth centuries achieved their success by absolutely reversing the method of Aristotle, by bringing into fruitful contact principles which he had condemned to barren isolation. They carried terrestrial physics into the heavens; they brought down the absoluteness and eternity of celestial law to earth; they showed that Aristotle’s antithetical qualities were merely quantitative distinctions. These they resolved into modes of motion; and they also resolved all motions into one, which was both rectilinear and perpetual. But they and their successors put an end to all dreams of transmutation, when they showed by another synthesis that all matter, at least within the limits of our experience, has the changeless consistency once attributed exclusively to the stellar spheres.

When Aristotle passes from the whole cosmos to the philosophy of life, his method of systematic division is less distinctly illustrated, but still it may be traced. The fundamental separation is between body and soul. The latter has a wider meaning than what we associate with it at present. It covers the psychic functions and the whole life of the organism, which, again, is not what we mean by life. For life with us is both individual and collective; it resides in each speck of protoplasm, and also in the consensus of the whole organism. With Aristotle it is more exclusively a central principle, the final cause of the organism, the power which holds it together, and by which it was originally shaped. Biology begins by determining the idea of the whole, and then considers the means by which it is realised. The psychic functions are arranged according to a system of teleological subordination. The lower precedes the higher in time, but is logically necessitated by it. Thus nutrition, or the vegetative life in general, must be studied in close connexion with sensation and impulse, or animal life; and this, again, with thought or pure reasoning. On the other hand, anatomy and physiology are considered from a purely chemical and mechanical point of view. A vital purpose is, indeed, assigned to every organ, but with no more reference to its specifically vital properties than if it formed part of a steam engine. Here, as always with Aristotle, the idea of moderation determines the point of view whence the inferior or material system is to be studied. Organic tissue is made up of the four elemental principles—hot, cold, wet, and dry—mixed together in proper proportions; and the object of organic function is to maintain them in due equilibrium, an end effected by the regulating power of the soul, which, accordingly, has its seat in the heart or centre of the body. It has been already shown how, in endeavouring to work out this chimerical theory, Aristotle went much further astray from the truth than sundry other Greek physiologists less biassed by the requirements of a symmetrical method.

After the formal and material elements of life have been separately discussed, there comes an account of the process by which they are first brought into connexion, for this is how Aristotle views generation. With him it is the information of matter by psychic force; and his notions about the part which each parent plays in the production of a new being are vitiated throughout by this mistaken assumption. Nevertheless his treatise on the subject is, for its time, one of the most wonderful works ever written, and, as we are told on good authority,[257] is now less antiquated than the corresponding researches of Harvey. The philosopher’s peculiar genius for observation, analysis, and comparison will partly account for his success; but, if we mistake not, there is another and less obvious reason. Here the fatal separation of form and matter was, except at first starting, precluded by the very idea of generation; and the teleological principle of spontaneous efforts to realise a predetermined end was, as it happened, perfectly in accordance with the facts themselves.

And now, looking back on his cosmology, we can see that Aristotle was never so near the truth as when he tried to bridge over the gulf between his two spheres, the one corruptible and the other eternal, by the idea of motion considered as a specific property of all matter, and persisting through all time; as a link between the celestial revolutions and the changes occurring on or near the earth’s surface; and, finally, as the direct cause of heat, the great agent acting in opposition to gravity—which last view may have suggested Bacon’s capital discovery, that heat is itself a mode of motion.

Another method by which Aristotle strove to overcome the antithesis between life as a mechanical arrangement and life as a metaphysical conception, was the newly created study of comparative anatomy. The variations in structure and function which accompany variations in the environment, though statically and not dynamically conceived, bring us very near to the truth that biological phenomena are subject to the same general laws of causation as all other phenomena; and it is this truth which, in the science of life, corresponds to the identification of terrestrial with celestial physics in the science of general mechanics. Vitality is not an individualised principle stationed in the heart and serving only to balance opposite forces against one another; but it is diffused through all the tissues, and bestows on them that extraordinary plasticity which responds to the actions of the environment by spontaneous variations capable of being summed up in any direction, and so creating entirely new organic forms without the intervention of any supernatural agency.