lustration.

The attack upon the Ideas is resumed in the Philebus, and is followed
by a return to a more rational philosophy. The perplexity of the One and
Many is there confined to the region of Ideas, and replaced by a theory
of classification; the Good arranged in classes is also contrasted with
the barren abstraction of the Megarians. The war is carried on against
the Eristics in all the later dialogues, sometimes with a playful irony,
at other times with a sort of contempt. But there is no lengthened
refutation of them. The Parmenides belongs to that stage of the
dialogues of Plato in which he is partially under their influence, using
them as a sort of 'critics or diviners' of the truth of his own, and of
the Eleatic theories. In the Theaetetus a similar negative dialectic
is employed in the attempt to define science, which after every effort
remains undefined still. The same question is revived from the objective
side in the Sophist: Being and Not-being are no longer exhibited in
opposition, but are now reconciled; and the true nature of Not-being is
discovered and made the basis of the correlation of ideas. Some
links are probably missing which might have been supplied if we had
trustworthy accounts of Plato's oral teaching.

To sum up: the Parmenides of Plato is a critique, first, of the Platonic
Ideas, and secondly, of the Eleatic doctrine of Being. Neither are
absolutely denied. But certain difficulties and consequences are shown
in the assumption of either, which prove that the Platonic as well as
the Eleatic doctrine must be remodelled. The negation and contradiction
which are involved in the conception of the One and Many are preliminary
to their final adjustment. The Platonic Ideas are tested by the
interrogative method of Socrates; the Eleatic One or Being is tried by
the severer and perhaps impossible method of hypothetical consequences,
negative and affirmative. In the latter we have an example of the
Zenonian or Megarian dialectic, which proceeded, not 'by assailing
premises, but conclusions'; this is worked out and improved by Plato.
When primary abstractions are used in every conceivable sense, any or
every conclusion may be deduced from them. The words 'one,' 'other,'
'being,' 'like,' 'same,' 'whole,' and their opposites, have slightly
different meanings, as they are applied to objects of thought or
objects of sense--to number, time, place, and to the higher ideas of
the reason;--and out of their d