But there can be no doubt as to his marvelous power of systematization. Collecting together all the results of ancient speculation, he so elaborated them into a coordinate system, that for two thousand years he reigned supreme in the schools. In a literary point of view, Plato was doubtless his superior, but Plato was a poet making philosophy divine and musical; but Aristotle's investigations spread over a far wider range. He wrote also on politics, natural history, and ethics, in so comprehensive and able manner, as to prove his claim to be one of the greatest intellects of antiquity, the most subtle and the most patient. He differed from Plato chiefly in relation to the doctrine of ideas, without however resolving the difficulty which divided them. As he made matter to be the eternal ground of phenomena, he reduced the notion of it to a precision it never before enjoyed, and established thereby a necessary element in human science. But being bound to matter, he did not soar, as Plato did, into the higher regions of speculation; nor did he entertain as lofty views of God, or of immortality. Neither did he have as high an ideal of human life. His definition of the highest good was a perfect practical activity in a perfect life. With Aristotle closed the great Socratic movement in the history of speculation. When Socrates appeared there was the general prevalence of skepticism, arising from the unsatisfactory speculations respecting nature. He removed this skepticism by inventing a new method, and by withdrawing the mind from the contemplation of nature, to the study of man himself. He bade men to look inward. [Sidenote: Ethics the great subject of inquiry with Plato.] Plato accepted his method, but applied it more universally. Like Socrates, however, ethics were the great subject of his inquiries, to which physics were only subordinate. The problem he sought to solve was the way to live like the gods. He would contemplate truth as the great aim of life. [Sidenote: Main inquiries of Aristotle had reference to physics and metaphysics.] With Aristotle, ethics formed only one branch of his attention. His main inquiries were in reference to physics and metaphysics. He thus, by bringing these into the region or inquiry, paved the way for a new epoch of skepticism. [Footnote: Lewes, Ritter, Hegel, Maurice, Diogenes Laertius. See fine article in _Encyclopedia Britannica._ Schwegler, translated by Seelyn.] It is impossible, within the proper limits of this chapter, to enter upon an analysis of the philosophy of either the three great lights of the ancient world, or to enumerate and describe their other writings. I merely wish to show what are considered to be the vital principles on which their systems were based, and the general spirit of their speculations. The student must examine these in the elaborate treatises of modern philosophers, and in the original works of Plato and Aristotle. [Sidenote: Their characteristic inquiries.]