At bottom Aristotle's philosophy is the same as Plato's, with some of the main defects and crudities removed. Plato was the founder of the philosophy of the Idea. [{332}] But in his hands, idealism was clogged with unessentials, and overgrown with excrescences. His crude theory of the soul as a thing mechanically forced in and out of the body, his doctrines of reincarnation and recollection, the belief that this thing the soul can travel to some place far away where it will see those things the Ideas, and above all, what is the root of all these, the confusion between reality and existence, with its consequent degradation of the universal to a mere particular--these were the unessentials with which Plato connected his essential idealism. To take the pure theory of Ideas--albeit not under that name--to purge it of these encumbrances and to cast them upon the rubbish heap, to cleanse Plato's gold of its dross, this was the task of Aristotle. Thought, the universal, the Idea, form--call it what you will--this is the ultimate reality, the foundation of the world, the absolute prius of all things. So thought both Plato and Aristotle. But whereas Plato began to draw mental pictures of the universal, to imagine that it existed apart in a world of its own, and so might be experienced by the vision of the wandering soul, Aristotle saw that this was to treat thought as if it were a thing, to turn it into a mere particular again. He saw that the universal, though it is the real, has no existence in a world of its own, but only in this world, only as a formative principle of particular things. This is the key-note of his philosophy. Aristotle registers, therefore, an enormous advance upon Plato. His system is the perfected and completed Greek idealism. It is the highest point reached in the philosophy of Greece. The flower of all previous thought, the essence and pure distillation of the Greek philosophic spirit, the gathering [{333}] up of all that is good in his predecessors and the rejection of all that is faulty and worthless--such is the philosophy of Aristotle. It was not possible for the Greek spirit to advance further. Further development could be only decay. And so, in fact, it turned out to be.
Aristotle deserves, too, the credit of having produced the only philosophy of evolution which the world has ever seen, with the exception of that of Hegel; and Hegel was enabled to found a newer theory of evolution only by following largely in the footsteps of Aristotle. This was perhaps Aristotle's most original contribution to thought. Yet the factors of the problem, though not its solution, he took from his predecessors. The problem of becoming had tortured Greek thought from the earliest ages. The philosophy of Heracleitus, in which it was most prominent, had failed to solve it. Heracleitus and his successors racked their brains to discover how becoming could be possible. But even if they had solved this minor problem, the greater question still remained in the background, what does this becoming mean? Becoming for them was only meaningless change. It was not development. The world-process was an endless stream of futile and purposeless events, "a tale, told by an idiot, full of sound and fury, signifying nothing." Aristotle not merely asked himself how becoming is possible. He showed that becoming has a meaning, that it signifies something, that the world-process is a rationally ordered development towards a rational end.
But, though Aristotle's philosophy is the highest presentation of the truth in ancient times, it cannot be accepted as anything final and faultless. Doubtless no philosophy can ever attain to finality. Let us apply our [{334}] two-fold test. Does his principle explain the world, and does it explain itself? First, does it explain the world? The cause of Plato's failure here was the dualism in his system between sense and thought, between matter and the Ideas. It was impossible to derive the world from the Ideas, because they were absolutely separated from the world. The gulf was so great that it could never be bridged. Matter and Idea lay apart, and could never be brought together. Now Aristotle saw this dualism in Plato, and attempted to surmount it. The universal and the particular, he said, do not thus lie apart, in different worlds. The Idea is not a thing here, and matter a thing there, so that these two incommensurables have to be somehow mechanically and violently forced together to form a world. Universal and particular, matter and form, are inseparable. The connexion between them is not mechanical, but organic. The dualism of Plato is thus admitted and refuted. But is it really surmounted? The answer must be in the negative. It is not enough by a tour de force to bring matter and form together, to assert that they are inseparable, while they remain all the time, in principle, separate entities. If the Absolute is form, matter ought to be deduced from form, shown to be merely a projection and manifestation of it. It must be shown that form not only moulds matter but produces it. If we assert that the one primal reality is form, then clearly we must prove that all else in the world, including matter, arises out of that prime being. Either matter arises out of form or it does not. If it does, this arising must be exhibited. If it does not, then form is not the sole ultimate reality, for matter is equally an ultimate, underivative, [{335}] primordial substance. In that case, we thus have two equally real ultimate beings, each underived from the other, existing side by side from all eternity. This is dualism, and this is the defect of Aristotle. Not only does he not derive matter from form, but he obviously sees no necessity for doing so. He would probably have protested against any attempt to do so, for, when he identifies the formal, final, and efficient causes with each other, leaving out the material cause, this is equivalent to an assertion that matter cannot be reduced to form. Thus his dualism is deliberate and persistent. The world, says Aristotle, is composed of matter and form. Where does this matter come from? As it does not, in his system, arise out of form, we can only conclude that its being is wholly in itself, i.e., that it is a substance, an absolute reality. And this is utterly inconsistent with Aristotle's assertion that it is in itself nothing but a mere potentiality. Thus, in the last resort, this dualism of sense and thought, of matter and Idea, of unlimited and limiting, which runs, "the little rift within the lute," through all Greek philosophy, is not resolved. The world is not explained, because it is not derived from a single principle. If form be the Absolute, the whole world must flow out of it. In Aristotle's system, it does not.
Secondly, is the principle of form self-explanatory? Here, again, we must answer negatively. Most of what was said of Plato under this head applies equally to Aristotle. Plato asserted that the Absolute is reason, and it was therefore incumbent on him to show that his account of reason was truly rational. He failed to do so. Aristotle asserts the same thing, for form is only [{336}] another word for reason. Hence he must show us that this form is a rational principle, and this means that he must show us that it is necessary. But he fails to do so. How is form a necessary and self-determining principle? Why should there be such a principle as form? We cannot see any necessity. It is a mere fact. It is nothing but an ultimate mystery. It is so, and that is an end of it. But why it should be so, we cannot see. Nor can we see why there should be any of the particular kinds of form that there are. To explain this, Aristotle ought to have shown that the forms constitute a systematic unity, that they can be deduced one from another, just as we saw that Plato ought to have deduced all the Ideas from one another. Thus Aristotle asserts that the form of plants is nutrition, of animals sensation, and that the one passes into the other. But even if this assertion be true, it is a mere fact. He ought not merely to have asserted this, but to have deduced sensation from nutrition. Instead of being content to allege that, as a fact, nutrition passes into sensation, he ought to have shown that it must pass into sensation, that the passage from one to the other is a logical necessity. Otherwise, we cannot see the reason why this change occurs. That is to say, the change is not explained.
Consider the effects of this omission upon the theory of evolution. We are told that the world-process moves towards an end, and that this end is the self-realization of reason, and that it is proximately attained in man, because man is a reasoning being. So far this is quite intelligible. But this implies that each step in evolution is higher than the last because it approaches nearer to [{337}] the end of the world-process. And as that end is the realization of reason, this is equivalent to saying that each step is higher than the last because it is more rational. But how is sensation more rational than nutrition? Why should it not be the other way about? Nutrition passes through sensation into human reason. But why should not sensation pass through nutrition into human reason? Why should not the order be reversed? We cannot explain. And such an admission is absolutely fatal to any philosophy of evolution. The whole object of such a philosophy is to make it clear to us why the higher form is higher, and why the lower is lower: why, for example, nutrition must, as lower, come first, and sensation second, and not vice versa. If we can see no reason why the order should not be reversed, this simply means that our philosophy of evolution has failed in its main point. It means that we cannot see any real difference between lower and higher, and that therefore we have merely change without development, since it is indifferent whether A passes into B, or B into A. The only way in which Aristotle could have surmounted these difficulties would have been to prove that sensation is a development of reason which goes beyond nutrition. And he could only do this by showing that sensation logically arises out of nutrition. For a logical development is the same as a rational development. He ought to have logically deduced sensation from nutrition, and so with all the other forms. As it is, all that can be said is that Aristotle was the founder of a philosophy of evolution because he saw that evolution implies movement towards an end, and because he attempted to point out the different stages in the attainment of that end, [{338}] but that he failed rationally to develop the doctrine stage by stage.
As neither the principle of form in general was shown to be necessary, nor were the particular forms deduced from each other, we have to conclude that Aristotle like Plato, named a self-explanatory principle, reason or form, as ultimate principle of things, but failed to show in detail that it is self-explanatory. Yet, in spite these defects, the philosophy of Aristotle is one of the greatest philosophies that the world has ever seen, or is ever likely to see. If it does not solve all problems, it does render the world more intelligible to us than it was before.
THE GENERAL CHARACTER OF POST-ARISTOTELIAN PHILOSOPHY
The rest of the story of Greek philosophy is soon told, for it is the story of decay. The post-Aristotelian is the least instructive of the three periods of Greek thought, and I shall delineate only its main outlines.