Plato

In the second and longer half, Parmenides gives an example of the logical training he recommends. He takes for examination his own thesis, "the One is," and constructs an elaborate set of an tinomies after the fashion of Zeno, apparently proving that whether this thesis be affirmed or denied, in either case we are compelled either to affirm simultaneously or to deny simultane ously a series of contradictory predicates, alike of the "One" and of the "Many." The conclusion is patently ironical, and we are left to divine the author's purpose, if we can.

The objections to "participation," which is formulated precisely as in the Phaedo, are directed not against the existence of Forms, but against the possibility that sensible things should "participate" in them. From the point of view of this criticism Socrates' error is that he attributes some sort of secondary reality to the sensible. The main arguments are two: (I) the doctrine does not really reconcile unity with plurality, since it leads to a regressus in inde finitum. It says that the many things which have a common predi cate "participate of" or "imitate" a single Form. But the Form itself also admits of the common predicate, and there must there fore be a second Form, "participated" or "imitated" alike by the sensible things and the first Form, and so on endlessly. We could not escape by the suggestion that the Form exists only "in our minds," since that would mean that a Form is a thought, and it would follow that "things" are made of thoughts. But if so, either everything thinks, or there are thoughts which do not think, and both alternatives are absurd; (2) it is a still graver difficulty that if there are two realms, a realm of Forms and a realm of sensible things, the relations between Forms must belong to the realm of Forms, those between sensible things to the realm of things. We ourselves belong to the second, and therefore all our knowledge belongs to it too; we know nothing of the true realities, the Forms : if anyone knows them, it is God, but God's knowledge, being knowledge of realities, will not extend to our world, the sensible. The purpose of the objections is thus to suggest that the "manifold of sense" has not even a derivative reality ; it is mere illusion.

This is precisely the position of the Eleatics and their Megarian continuators. The inference is that Plato is reproducing Megarian criticisms of the doctrine ascribed by himself to Socrates, an in ference confirmed by the notice preserved by Alexander of Aphro disiac (on Met. 990 b 15) of the "third man" argument of the Megarian Polyxenus against "participation." Plato does not indi

cate his own opinion of the cogency of the reasoning, which is, in fact, fallacious, as was properly pointed out by Proclus.' The purpose of the antinomies which follow has been very dif ferently understood. In the present writer's opinion, they are de liberate parody, the object being to show that the methods of the Megarian logicians are even more damaging to their own funda mental metaphysical tenet than they are to the doctrine of "par ticipation." Megarian logic is a double-edged weapon, and Plato, if he chooses, can apply it even more dexterously than its inventors.

Theaetetus.

Except for a magnificent interlude in praise of the contemplative life, the dialogue is a straightforward discussion of the question how knowledge should be defined. It naturally ends negatively. None of the proposed definitions will stand ex amination (the reason is that we are really trying to define truth and truth is an ultimate). But the incidental results of the dis cussion are of the first importance. We learn (a) that knowledge cannot be identified with sensation nor with any formless "simple apprehension"; (b) that pure relativism is as impossible in epis temology as in metaphysics. We have the beginning of a doctrine of the "categories" which is further developed in the Sophistes.

The increasing value which Plato is coming to put upon "natural knowledge" is marked by the use of the. word 84a, which in earlier dialogues had commonly meant mere uncertain "opinion" as contrasted with knowledge, in the new sense of "judgment" which it retains in Plato's subsequent work. The most striking negative feature of the Theaetetus is that it discusses knowledge at length without making any reference to the Forms and the mythology of "recollection." It remains to this day the best of introductions to the "problem of knowledge." The main argument may be very briefly summarized thus : I. It seems plausible at first to say that knowledge (frcarihun) is sen sation This sounds very much like the proposition of Protagoras, "what seems to me is so to me; what seems to you is so to you." We might base such a thorough-going doctrine of the relativity of all knowledge on a still more ultimate meta physical theory, if we said—it is implied that Protagoras himself said nothing of the kind—that, within us and without us, the only reality is motion. "Organ" and "environment" are both motions ; when these motions impinge on one another, they give rise to the twin-product, felt sensation–sensible quality.