Here we have, first of all, an unmistakable attack made by the youthful Socrates on the paradoxes of Zeno. He perfectly understands their drift, and Zeno himself is supposed to admit this. But they appear to him, as he says in the Philebus also, to be rather truisms than paradoxes. For every one must acknowledge the obvious fact, that the body being one has many members, and that, in a thousand ways, the like partakes of the unlike, the many of the one. The real difficulty begins with the relations of ideas in themselves, whether of the one and many, or of any other ideas, to one another and to the mind. But this was a problem which the Eleatic philosophers had never considered; their thoughts had not gone beyond the contradictions of matter, motion, space, and the like.
It was no wonder that Parmenides and Zeno should hear the novel speculations of Socrates with mixed feelings of admiration and displeasure. He was going out of the received circle of disputation into a region in which they could hardly follow him. From the crude idea of Being in the abstract, he was about to proceed to universals or general notions. There is no contradiction in material things partaking of the ideas of one and many; neither is there any contradiction in the ideas of one and many, like and unlike, in themselves. But the contradiction arises when we attempt to conceive ideas in their connexion, or to ascertain their relation to phenomena. Still he affirms the existence of such ideas; and this is the position which is now in turn submitted to the criticisms of Parmenides.
To appreciate truly the character of these criticisms, we must remember the place held by Parmenides in the history of Greek philosophy. He is the founder of idealism, and also of dialectic, or, in modern phraseology, of metaphysics and logic (Theaet., Soph.). Like Plato, he is struggling after something wider and deeper than satisfied the contemporary Pythagoreans. And Plato with a true instinct recognizes him as his spiritual father, whom he 'revered and honoured more than all other philosophers together.' He may be supposed to have thought more than he said, or was able to express. And, although he could not, as a matter of fact, have criticized the ideas of Plato without an anachronism, the criticism is appropriately placed in the mouth of the founder of the ideal philosophy.
There was probably a time in the life of Plato when the ethical teaching of Socrates came into conflict with the metaphysical theories of the earlier philosophers, and he sought to supplement the one by the other. The older philosophers were great and awful; and they had the charm of antiquity. Something which found a response in his own mind seemed to have been lost as well as gained in the Socratic dialectic. He felt no incongruity in the veteran Parmenides correcting the youthful Socrates. Two points in his criticism are especially deserving of notice. First of all, Parmenides tries him by the test of consistency. Socrates is willing to assume ideas or principles of the just, the beautiful, the good, and to extend them to man (compare Phaedo); but he is reluctant to admit that there are general ideas of hair, mud, filth, etc. There is an ethical universal or idea, but is there also a universal of physics? – of the meanest things in the world as well as of the greatest? Parmenides rebukes this want of consistency in Socrates, which he attributes to his youth. As he grows older, philosophy will take a firmer hold of him, and then he will despise neither great things nor small, and he will think less of the opinions of mankind (compare Soph.). Here is lightly touched one of the most familiar principles of modern philosophy, that in the meanest operations of nature, as well as in the noblest, in mud and filth, as well as in the sun and stars, great truths are contained. At the same time, we may note also the transition in the mind of Plato, to which Aristotle alludes (Met.), when, as he says, he transferred the Socratic universal of ethics to the whole of nature.
The other criticism of Parmenides on Socrates attributes to him a want of practice in dialectic. He has observed this deficiency in him when talking to Aristoteles on a previous occasion. Plato seems to imply that there was something more in the dialectic of Zeno than in the mere interrogation of Socrates. Here, again, he may perhaps be describing the process which his own mind went through when he first became more intimately acquainted, whether at Megara or elsewhere, with the Eleatic and Megarian philosophers. Still, Parmenides does not deny to Socrates the credit of having gone beyond them in seeking to apply the paradoxes of Zeno to ideas; and this is the application which he himself makes of them in the latter part of the dialogue. He then proceeds to explain to him the sort of mental gymnastic which he should practise. He should consider not only what would follow from a given hypothesis, but what would follow from the denial of it, to that which is the subject of the hypothesis, and to all other things. There is no trace in the Memorabilia of Xenophon of any such method being attributed to Socrates; nor is the dialectic here spoken of that 'favourite method' of proceeding by regular divisions, which is described in the Phaedrus and Philebus, and of which examples are given in the Politicus and in the Sophist. It is expressly spoken of as the method which Socrates had heard Zeno practise in the days of his youth (compare Soph.).
The discussion of Socrates with Parmenides is one of the most remarkable passages in Plato. Few writers have ever been able to anticipate 'the criticism of the morrow' on their favourite notions. But Plato may here be said to anticipate the judgment not only of the morrow, but of all after-ages on the Platonic Ideas. For in some points he touches questions which have not yet received their solution in modern philosophy.
The first difficulty which Parmenides raises respecting the Platonic ideas relates to the manner in which individuals are connected with them. Do they participate in the ideas, or do they merely resemble them? Parmenides shows that objections may be urged against either of these modes of conceiving the connection. Things are little by partaking of littleness, great by partaking of greatness, and the like. But they cannot partake of a part of greatness, for that will not make them great, etc.; nor can each object monopolise the whole.