Introd, xxxi.-ii., lii-v. Does Plato now go on to
talk metaphysics in a mystery, does he refute Par-
menides’ doctrine out of its author’s own mouth,
or does he merely give a lesson in dialectic? Such
are some of the suggestions. Except that the
second might better run, does he develop what is
latent in the doctrine of Parmenides ?—there is no
inconsistency in supposing that he does all these
at once, and advances his own conception of the
ideal problem at the same time. Among the
thoughts which succeed each other in his mind as
he writes, one is that there is complexity within the
ideal world analogous to that in our sensible one:
a second is that the ideas having so far been held
to be isolated, as a sina qua non of their purity,
hopeless contradictions thus arise which cut at the
very roots of philosophy : a third is that some such
trenchant dialectic as that exemplified by Zeno’s
writings is essential if these difficulties are to be
overcome; and that a laborious discipline in it is
the sole training adequate for him who would deal
with the ideal theory, or (which to Plato is the
same thing) with metaphysical problems at all. It
is clear from the detail given that Plato has this
last subject deeply at heart. As upshot, Parm. is,
as it were, put to revise his own doctrine in the
light of more recent developments. And the
result seems to be that even the simple idea of
‘one’ has indefinite possibilities latent in it, and
that, so far from its being possible to regard any
idea as isolated, an almost Heraclitean complexity
in the ideal sphere arising through dialectical neces-
sities is now the real problem to be faced. Dialectic,
says Aristotle (Met. 1.6; xu. 4), did not exist before
this; and the more Plato looks into it as a factor
in speculation the more impressed he is with its
transforming powers—in physical matters it has
infinitely divided the space between Achilles and
the tortoise, so that we can hardly think of the one
overtaking the other: in the intellectual sphere it
converts even the simple unity of being as put
forth by Parmenides into endless multiplicity. It
is curious to observe, however, that the ‘idea of
science’ quietly drops out of sight. 