From, A History of Greek Philosophy, vol. IV, Plato: the man and his dialogues, earlier period,
Cambridge University Press, 19896, pp. 8-38.
In the dialogues, there is no need to emphasize the fact that Plato’s chief inspiration for the greater part of his life was Socrates. In the great majority of them he takes the lead throughout, even in the Theaetetus and Philebus which must have been written in Plato’s late maturity. In this period however we shall have to consider the significance of a striking change. In the Parmenides, Socrates is a young man quite overshadowed by the elderly and revered Parmenides and though his part at the beginning is important, he is silent for four—fifths of the whole. In the Sophist and Ροliticus, which follow the Theaetetus, he gives place to the unnamed Eleatic visitor after a few introductory remarks, and similarly in the Timaeus to the Pythagorean Timaeus from Locri.
Of Presocratic cosmogonical and physiological theories Plato shows his general knowledge in the famous passage in the Phaedo (95e ff.) where Socrates says that to answer adequately the question of Cebes he must go into the whole question of how things come into being and perish. The influence of Heraclitus is seen in the Symposium (207d) when Diotima describes our bodies as being in a constant process of change and renewal throughout our lives, affecting hair, flesh, bones, blood and all the rest. Cratylus 402a quotes Heraclitus by name for his famous comparison οf the world to a river into which you cannot step twice (νol. I, 488ff.). At Theaetetus 152e he is mentioned together with Protagoras and Empedocles as a believer in the genesis of all things from motion and mingling, in contrast to Parmenides, the only one who denied motion; and later in the same dialogue the Heracliteans are satirized as people impossible to deal with (179e ff.). Faithful to their doctrine they are in perpetual motion. They cannot argue, but shoot out little riddling phrases like arrows, and there are no teachers or pupils among them, for each thinks he is inspired and the others know nothing. One is reminded of Aristotle’s hit at Cratylus, who, he says (Metaphysics 1010a10-15), was so overcome by the impossibility οf arresting even for a moment the flux οf change that in the end he found any speech impossible and merely moved his finger. At Sophist 242d (νol, I, 436 f.) Plato shows that he appreciated the full paradoxical rigour of Heraclitus’s teaching, which most others missed.
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