awkward consequences. We cannot say "this is white," for if it was white when we began
speaking it will have ceased to be white before we end our sentence. We cannot be right in
saying we are seeing a thing, for seeing is perpetually changing into not-seeing. * If everything
is changing in every kind of way, seeing has no right to be called seeing rather than not-seeing,
or perception to be called perception rather than not-perception. And when we say "perception
is knowledge," we might just as well say "perception is not-knowledge."
What the above argument amounts to is that, whatever else may be in perpetual flux, the
meanings of words must be fixed, at least for a time, since otherwise no assertion is definite,
and no assertion is true rather than false. There must be something more or less constant, if
discourse and knowledge are to be possible. This, I think, should be admitted. But a great deal
of flux is compatible with this admission.
There is, at this point, a refusal to discuss Parmenides, on the ground that he is too great and
grand. He is a "reverend and awful figure." "There was a sort of depth in him that was
altogether noble." He is "one being whom I respect above all." In these remarks Plato shows his
love for a static universe, and his dislike of the Heraclitean flux which he has been admitting for
the sake of argument. But after this expression of reverence he abstains from developing the
Parmenidean alternative to Heraclitus.
We now reach Plato's final argument against the identification of knowledge with perception.
He begins by pointing out that we perceive through eyes and ears, rather than with them, and he
goes on to point out that some of our knowledge is not connected with any sense-organ. We can
know, for instance, that sounds and colours are unlike, though no organ of sense can perceive
both. There is no special organ for "existence and non-existence, likeness and unlikeness,
sameness and differences, and also unity and numbers in general." The same applies to
honourable and dishonourable, and good and bad. "The mind contemplates some things through
its own instrumentality, others through the bodily faculties." We perceive hard and soft through
touch, but it is the mind that judges that they exist and that they are contraries. Only the mind
can reach existence, and we can-
* Compare the advertisement: "That's Shell, that was."-152-not reach truth if we do not reach existence. It follows that we cannot know things through the
senses alone, since through the senses alone we cannot know that things exist. Therefore
knowledge consists in reflection, not in impressions, and perception is not knowledge, because
it "has no part in apprehending truth, since it has none in apprehending existence."To
disentangle what can be accepted from what must be rejected in this argument against the
identification of knowledge with perception is by no means easy. There are three inter-
connected theses that Plato discusses, namely:
- Knowledge is perception;
- Man is the measure of all things;
- Everything is in a state of flux.