produced a magnificent effect by expounding to us that he was no wiser than
a tadpole. For if sensations are always true, and one man's discernment is
as good as another's, and every man is his own judge, and everything that
he judges is right and true, then what need of Protagoras to be our
instructor at a high figure; and why should we be less knowing than he is,
or have to go to him, if every man is the measure of all things? My own
art of midwifery, and all dialectic, is an enormous folly, if Protagoras'
"Truth" be indeed truth, and the philosopher is not merely amusing himself
by giving oracles out of his book.'

Theodorus thinks that Socrates is unjust to his master, Protagoras; but he
is too old and stiff to try a fall with him, and therefore refers him to
Theaetetus, who is already driven out of his former opinion by the
arguments of Socrates.

Socrates then takes up the defence of Protagoras, who is supposed to reply
in his own person--'Good people, you sit and declaim about the gods, of
whose existence or non-existence I have nothing to say, or you discourse
about man being reduced to the level of the brutes; but what proof have you
of your statements? And yet surely you and Theodorus had better reflect
whether probability is a safe guide. Theodorus would be a bad geometrician
if he had nothing better to offer.'...Theaetetus is affected by the appeal
to geometry, and Socrates is induced by him to put the question in a new
form. He proceeds as follows:--'Should we say that we know what we see and
hear,--e.g. the sound of words or the sight of letters in a foreign
tongue?'

'We should say that the figures of the letters, and the pitch of the voice
in uttering them, were known to us, but not the meaning of them.'