to speak of himself.

The other digression is the famous contrast of the lawyer and
philosopher. This is a sort of landing-place or break in the middle of
the dialogue. At the commencement of a great discussion, the reflection
naturally arises, How happy are they who, like the philosopher, have
time for such discussions (compare Republic)! There is no reason for the
introduction of such a digression; nor is a reason always needed, any
more than for the introduction of an episode in a poem, or of a topic in
conversation. That which is given by Socrates is quite sufficient, viz.
that the philosopher may talk and write as he pleases. But though not
very closely connected, neither is the digression out of keeping with
the rest of the dialogue. The philosopher naturally desires to pour
forth the thoughts which are always present to him, and to discourse of
the higher life. The idea of knowledge, although hard to be defined, is
realised in the life of philosophy. And the contrast is the favourite
antithesis between the world, in the various characters of sophist,
lawyer, statesman, speaker, and the philosopher,--between opinion and
knowledge,--between the conventional and the true.

The greater part of the dialogue is devoted to setting up and throwing
down definitions of science and knowledge. Proceeding from the lower to
the higher by three stages, in which perception, opinion, reasoning are
successively examined, we first get rid of the confusion of the idea of
knowledge and specific kinds of knowledge,--a confusion which has been
already noticed in the Lysis, Laches, Meno, and other dialogues. In
the infancy of logic, a form of thought has to be invented before the
content can be filled up. We cannot define knowledge until the nature of
definition has been ascertained. Having succeeded in making his meaning
plain, Socrates proceeds to analyze (1) the first definition which
Theaetetus proposes: 'Knowledge is sensible perception.' This is
speedily identified with the Protagorean saying, 'Man is the measure
of all things;' and of this again the foundation is discovered in the
perpetual flux of Heracleitus. The relativeness of sensation is then
developed at length, and for a moment the definition appears to be
accepted. But soon the Protagorean thesis is pronounced to be suicidal;
for the adversaries of Protagoras are as good a measure as he is, and
they deny his doctrine. He is then supposed to reply that the perception
may