Timaeus

obviously, our business is to investigate his mode of operation at both stages. We must see how he endeavored in the first instance to escape the philosophical skepticism that seemed the inevitable result of previous speculation, what deficiencies he found in the earlier form of his theory, and how he proposed to remedy its faults. We must also observe how his conception of the nature of the problem may have altered in the interval between the earlier and later phases of the ideal theory.

To this end, it will be necessary to examine Plato’s metaphysical teaching as propounded in a group of dialogues. The most important of these metaphysically are the Republic and Phaedo—with which the Phaedrus, Symposium, Meno, and apparently the Cratylus are in accordance—and next, the amended form of their teaching as it appears in four great dialogues of the later period: Parmenides, Sophist, Philebus, and Timaeus, especially, of course, the last. The Socratic dialogues may be dismissed as not bearing upon our question.

Plato starts from a Herakleitean standpoint. § 16. Plato had thoroughly assimilated the physical teaching of Herakleitos. He held, no less strongly than the Ionian philosopher, the utter instability and fluidity of material nature. While we are not perhaps at liberty to cite the very emphatic language of the Theaetetus as evidence of his view in the earlier phase of his philosophy—which we are currently addressing—there is abundant proof within the limits of the Republic and Phaedo (see Republic 479 B, Phaedo 78 B). He was therefore, like Protagoras, bound to draw his inference from the Herakleitean principle. The inference drawn by Protagoras was that speculation is idle and knowledge impossible. The inference drawn by Plato was that, since matter cannot be known, there must be some essence transcending matter which alone is the object of knowledge. Furthermore, this immaterial essence must be the cause and sole reality of material phenomena. Thus, it was Plato’s acceptance of the Herakleitean πάντα ῥεῖ original: "everything flows", combined with his refusal to infer from it the impossibility of knowledge, that led him to idealism.

The contribution of Sokrates, and the ideal theory as presented in the Republic. At this point, the hint from Sokrates is incorporated. What manner of immaterial essence are we to seek as the object of knowledge? Plato cordially adopted the Socratic principle that universals alone can be known. But the Socratic universal, being no substantial existence but merely a conception in our own mind, will not meet Plato’s demand for a