From, A History of Greek Philosophy, vol. IV, Plato: the man and his dialogues, earlier period,
Cambridge University Press, 19896, pp. 8-38.
The greatest single influence on Plato after Socrates was Parmenides, that giant of intellect among the Presocratics whose challenging thesis that by all rational argument motion and change were impossible had to be met without evading his apparently unassailable premises. Ι have referred already to the dialogues in which he, or an Eleatic follower, takes the lead, and in the Theaetetus (183e) Socrates refuses to embark on a criticism of Parmenides because he has always thought of him as, in the words of Homer, a ‘reverend and awful’ figure. There is no trace of irony in this description. Here and again at Sophist 217c Plato makes him refer to his (doubtless imaginary) meeting with Parmenides in his youth which is the subject of the Parmenides. Actual quotations from Parmenides’s poem occur at Symposium 178b and Sophist 237a. Much of the Sophist is devoted to an examination of his use of the verb ‘to be’ solely in an absolute sense, with its consequence that, as he claimed, ‘what is not’ can be neither spoken nor thought of. The mischievous use by Sophists of the exclusive choice between ‘being’ and ‘not-being’ was satirized by Plato in the Euthydemus, where it is argued, for example, that to wish for someone to be no longer what he is (i.e. ignorant) is, after all, to wish him to be no longer, i.e. to perish (283 c-d). In the Sophist he had to go to some trouble to show that ‘what is not, in some respects has being’, because ‘is not’ might mean only ‘is different from’. The other way in which, at an earlier stage, Plato modified the harsh dichotomy of Parmenides was by introducing an intermediate ontological category between being and non-being, namely the world of becoming. Not having the status of full, unchanging being, it could not be the object of full knowledge, but only of doxa, belief or opinion. Nevertheless the ‘beliefs of mortals’ were not wholly false as Parmenides had claimed (fr. 1.30), but somewhere between knowledge and ignorance as their subject was between the being of the Forms and sheer nonentity.
Since much of Plato’s philosophy is unimaginable without the towering figure of Parmenides, it will seem surprising that he is not mentioned by Aristotle in his account of the genesis of the theory of Forms. A probable explanation, if not a justification, is that this occurs in his examination of earlier views on a particular subject, the causes of coming-to-be and perishing. That Plato investigated these he admits, but since Parmenides and his followers simply denied that motion and coming-to-be take place in reality at all, they must, he says (986b12-17, 25-6), be set aside ‘as inappropriate to the present investigation of causes’.
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