II.

Ever since the age of Parmenides and Heracleitus, Greek thought had been haunted by a pervading dualism which each system had in turn attempted to reconcile, with no better result than its reproduction under altered names. And speculation had latterly become still further perplexed by the question whether the antithetical couples supposed to divide all Nature between them could or could not be reduced to so many aspects of a single opposition. In the last chapter but one we showed that there were four such competing pairs—Being and Not-Being, the One and the Many, the Same and the Other, Rest and Motion. Plato employed his very subtlest dialectic in tracing out their connexions, readjusting their relationships, and diminishing the total number of terms which they involved. In what was probably his last great speculative effort, the _Timaeus_, he seems to have selected Sameness and Difference as the couple best adapted to bear the heaviest strain of thought. There is some reason for believing that in his spoken lectures he followed the Pythagorean system more closely, giving the preference to the One and the Many; or he may have employed the two expressions indifferently. The former would sooner commend itself to a dialectician, the latter to a mathematician. Aristotle was both, but he was before all things a naturalist. As such, the antithesis of Being and Not-Being, to which Plato attached little or no value, suited him best. Accordingly, he proceeds to work it out with a clearness before unknown in Greek philosophy. The first and surest of all principles, he declares, is, that a thing cannot both be and not be, in the same sense of the words, and furthermore that it must either be or not be. Subsequent logicians prefixed to these axioms another, declaring that whatever is is. The three together are known as the laws of Identity, Contradiction, and Excluded Middle. By all, except Hegelians, they are recognised as the highest laws of thought; and even Hegel was indebted to them, through Fichte, for the ground-plan of his entire system.[235]

The whole meaning and value of such excessively abstract propositions must lie in their application to the problems which they are employed to solve. Aristotle made at once too much and too little of his. Too much—for he employed them to refute doctrines not really involving any logical inconsistency—the theory of Heracleitus, that everything is in motion; the theory of Anaxagoras, that everything was originally confused together; the theory of Protagoras, that man is the measure of all things. Too little—for he admitted a sphere of possibilities where logical definition did not apply, and where subjects simultaneously possessed the capacity of taking on one or other of two contradictory attributes.

Nor is this all. After sharply distinguishing what is from what is not, and refusing to admit any intermediary between them, Aristotle proceeds to discover such an intermediary in the shape of what he calls Accidental Predication.[236] An accident is an attribute not necessarily or usually inhering in its subject—in other words, a co-existence not dependent on causation. Aristotle could never distinguish between the two notions of cause and kind, nor yet between interferences with the action of some particular cause and exceptions to the law of causation in general; and so he could not frame an intelligible theory of chance. Some propositions, he tells us, are necessarily true, others are only generally true; and it is the exceptions to the latter which constitute accident; as, for instance, when a cold day happens to come in the middle of summer. So also a man is necessarily an animal, but only exceptionally white. Such distinctions are not uninteresting, for they prove with what difficulties the idea of invariable sequence had to contend before even the highest intellects could grasp it. There was a constant liability to confound the order of succession with the order of co-existence, the order of our sensations with the order of objective existence, and the subjection of human actions to any fixed order, with the impossibility of deliberation and choice. The earlier Greek thinkers had proclaimed that all things existed by necessity; but with their purely geometrical or historical point of view, they entirely ignored the more complex questions raised by theories about classification, logical attribution, and moral responsibility. And the modifications introduced by Epicurus, into the old physics, show us how unanswerable Aristotle’s reasonings seemed to some of his ablest successors.

Absolute being is next distinguished from truth, which, we are told, has no objective existence[237]—a remarkable declaration, which throws much light on other parts of the Aristotelian system, and to which we shall subsequently return.[238]

After explaining at considerable length what Being is not, Aristotle now proceeds to ascertain what it is. He tells us that just as all number _quâ_ number must be either odd or even, so all Being _quâ_ Being must have certain universal attributes. These he sets himself to discover. When Descartes long afterwards entered on a somewhat similar inquiry, he fell back on the facts of his own individual consciousness. Aristotle, on the contrary, appeals to the common consciousness of mankind as embodied in ordinary language. In how many senses do we say that a thing is? The first answer is contained in his famous Ten Categories.[239] These are not what some have supposed them to be, _summa genera_ of existence, but _summa genera_ of predication. In other words, they are not a classification of things, but of the information which it is possible to receive about a single thing, more especially about the richest and most concrete thing known to us—a human being. If we want to find out all about a thing we ask, What is it? Of what sort? How large? To what does it belong? Where and when can we find it? What does it do? What happens to it? And if the object of our investigations be a living thing, we may add, What are its habits and dispositions? The question has been raised, how Aristotle came to think of these ten particular categories, and a wonderful amount of rubbish has been written on the subject, while apparently no scholar could see what was staring him in the face all the time, that Aristotle got them by collecting all the simple forms of interrogation supplied by the Greek language,[240] and writing out their most general expressions.

Having obtained his categories, Aristotle proceeds to mark off the first from the other nine. The subject or substance named in answer to the question, What is it? can exist without having any quality, size, and so forth predicated of it; but they cannot exist without it. Logically, they cannot be defined without telling _what_ they are; really they cannot be conceived without something not themselves in which they inhere. They are like the tail of a kite, giving greater conspicuousness and buoyancy to the body, but entirely dependent on it for support. What our philosopher fails to perceive is, that the dependence is reciprocal, that substance can no more be conceived without attributes than attributes without substance; or rather that substance, like all other categories, can be resolved into Relation.[241]

Meanwhile, he had a logical machine ready to hand, which could be used with terrible effect against the Platonic Ideas. Any of these—and there were a great number—that could be brought under one of the last nine categories were at once deprived of all claim to independent existence. Take Equality, for instance. It cannot be discovered outside quantity, and quantity is always predicated of a substance. And the same is true of number, to the utter destruction of the Neo-Pythagorean theory which gave it a separate existence. Moreover, the categories served not only to generalise and combine, but also to specificate and divide. The idea of motion occurs in three of them; in quantity, where it means increase or diminution; in quality, where it means alteration, as from hot to cold, or _vice versâ_; and in place, implying transport from one point to another. The Idea of Good, which stands at the very summit of Plato’s system, may be traced through all ten categories.[242] Thus, the supposed unity and simplicity of such conceptions was shown to be an illusion. Platonism was, in truth, so inconsistent with the notions embodied in common language, that it could not but be condemned by a logic based on those notions.

Aristotle next takes the Idea of Substance and subjects it to a fresh analysis.[243] Of all things none seem to possess so evident an existence as the bodies about us—plants and animals, the four elements, and the stars. But each of these has already been shown to consist of Form and Matter. A statue, for instance, is a lump of bronze shaped into the figure of a man. Of these two constituents, Matter seems at first sight to possess the greater reality. The same line of thought which led Aristotle to place substance before the other categories now threatens to drive him back into materialism. This he dreaded, not on sentimental or religious grounds, but because he conceived it to be the negation of knowledge. He first shows that Matter cannot be the real substance to which individuals owe their determinate existence, since it is merely the unknown residuum left behind when every predicate, common to them with others, has been stripped off. Substance, then, must be either Form alone or Form combined with Matter. Form, in its completest sense, is equivalent to the essential definition of a thing—the collection of attributes together constituting its essence or conception. To know the definition is to know the thing defined. The way to define is to begin with the most general notion, and proceed by adding one specific difference after another, until we reach the most particular and concrete expression. The union of this last with a certain portion of Matter gives us the individual Socrates or Callias. There are no real entities (as the Platonists pretend) corresponding to the successive stages of generalisation, biped, animal, and so forth, any more than there are self-existing quantities, qualities, and relations. Thus the problem has been driven into narrower and narrower limits, until at last we are left with the _infimæ species_ and the individuals contained under them. It remains to discover in what relation these stand to one another. The answer is unsatisfactory. We are told that there is no definition of individuals, and also that the definition is identical with the individual.[244] Such, indeed, is the conclusion necessarily resulting from Aristotle’s repeated declarations that all knowledge is of definitions, that all knowledge is of something really existing, and that nothing really exists but individual things. Nevertheless, against these we have to set equally strong declarations to the effect that knowledge is of something general, not of the perishing individuals which may pass out of existence at any moment. The truth is, that we are here, as Zeller has shown,[245] in presence of an insoluble contradiction, and we must try to explain, not how Aristotle reconciled it with itself, for that was impossible, but how he reconciled himself to it.

His analysis of individuality was the first step in this direction. We have seen that he treats definition as a process of gradual specification, beginning with the most general notions, and working down by successive differentiations to the most particular. Now, the completed conception is itself the integration of all these differences, the bond of union holding them together. Turning to an antithetical order of ideas, to the material substance of which bodies are composed, and its various transformations, we find him working out the same vein of thought. According to the Aristotelian chemistry, an ultimate indeterminate unknowable something clothes itself with one or other of the opposing attributes, dry and moist, hot and cold; and when two of these are combined, manifests itself to our senses as one of the four elements. The elements combine in a particular manner to form homogeneous animal tissues, and these again are united into heterogeneous organs, which together constitute the living body. Here, then, we have two analogous series of specifications—one conceptual and leading down from the abstract to the concrete, the other physical, and leading up from the vague, the simple, and the homogeneous, to the definite, the complex, and the heterogeneous. Aristotle embraces both processes under a single comprehensive generalisation. He describes each of them as the continuous conversion of a possibility into an actuality. For the sake of greater clearness, let us take the liberty of substituting modern scientific terms for his cumbrous and obsolete classifications. We shall then say that the general notion, living thing, contains under it the two less general notions—plant and animal. If we only know of any given object that it has life, there is implied the possibility of its being either the one or the other, but not both together. On determining it to be (say) an animal, we actualise one of the possibilities. But the actualisation is only relative, and immediately becomes the possibility of being either a vertebrate or an invertebrate animal. The actuality vertebrate becomes the possibility of viviparous or oviparous, and so on through successive differentiations until we come (say) to a man. Now let us begin at the material end. Here are a mass of molecules, which, in their actual state are only carbon, nitrogen, and so forth. But they are potential starch, gluten, water, or any other article of food that might be named; for under favourable conditions they will combine to form it. Once actualised as such, they are possible blood-cells; these are possible tissues; these, again, possible organs, and lastly we come to the consensus of vital functions, which is a man. What the raw material is to the finished product, that are the parts to the entire organism, the elements to the compound, the genus to the species, and such in its very widest sense is potency to realisation, δύναμις to ἐντελέχεια, throughout the universe of growth and decay.[246]

It will be observed that, so far, this famous theory does not add one single jot to our knowledge. Under the guise of an explanation, it is a description of the very facts needing to be explained. We did not want an Aristotle to tell us that before a thing exists it must be possible. We want to know how it is possible, what are the real conditions of its existence, and why they combine at a particular moment to produce it. The Atomists showed in what direction the solution should be sought, and all subsequent progress has been due to a development of their method. Future ages will perhaps consider our own continued distinction between force and motion as a survival of the Peripatetic philosophy. Just as sensible aggregates of matter arise not out of potential matter, but out of matter in an extremely fine state of diffusion, so also sensible motion will be universally traced back, not to potential motion, which is all that force means, but to molecular or ethereal vibrations, like those known to constitute heat and light.

We have said, in comparing him with his predecessors, that the Stagirite unrolled Greek thought from a solid into a continuous surface. We have now to add that he gave his surface the false appearance of a solid by the use of shadows, and of aërial perspective. In other words, he made the indication of his own ignorance and confusion do duty for depth and distance. For to say that a thing is developed out of its possibility, merely means that it is developed out of something, the nature of which we do not know. And to speak about such possibilities as imperfect existences, or matter, or whatever else Aristotle may be pleased to call them, is simply constructing the universe, not out of our ideas, but out of our absolute want of ideas.

We have seen how, for the antithesis between Form and Matter, was substituted the wider antithesis between Actuality and Possibility. Even in this latter the opposition is more apparent than real. A permanent possibility is only intelligible through the idea of its realisation, and sooner or later is certain to be realised. Aristotle still further bridges over the interval between them by a new conception—that of motion. Motion, he tells us, is the process of realisation, the transformation of power into act. Nearly the whole of his _Physics_ is occupied with an enquiry into its nature and origin. As first conceived, it is equivalent to what we call change rather than to mechanical movement. The table of categories supplies an exhaustive enumeration of its varieties. These are, as we have already mentioned, alteration of quality or transformation, increase or decrease of quantity, equivalent to growth and decay, and transport from place to place. Sometimes a fourth variety is added, derived from the first category, substance. He calls it generation and destruction, the coming into existence or passing out of it again. A careful analysis shows that motion in space is the primordial change on which all others depend for their accomplishment. To account for it is the most vitally important problem in philosophy.