of the dialogue, with the Sophist, to which in many respects the Theaetetus
is so little akin. (1) The same persons reappear, including the younger
Socrates, whose name is just mentioned in the Theaetetus; (2) the theory of
rest, which Socrates has declined to consider, is resumed by the Eleatic
Stranger; (3) there is a similar allusion in both dialogues to the meeting
of Parmenides and Socrates (Theaet., Soph.); and (4) the inquiry into not-
being in the Sophist supplements the question of false opinion which is
raised in the Theaetetus. (Compare also Theaet. and Soph. for parallel
turns of thought.) Secondly, the later date of the dialogue is confirmed
by the absence of the doctrine of recollection and of any doctrine of ideas
except that which derives them from generalization and from reflection of
the mind upon itself. The general character of the Theaetetus is
dialectical, and there are traces of the same Megarian influences which
appear in the Parmenides, and which later writers, in their matter of fact
way, have explained by the residence of Plato at Megara. Socrates
disclaims the character of a professional eristic, and also, with a sort of
ironical admiration, expresses his inability to attain the Megarian
precision in the use of terms. Yet he too employs a similar sophistical
skill in overturning every conceivable theory of knowledge.

The direct indications of a date amount to no more than this: the
conversation is said to have taken place when Theaetetus was a youth, and
shortly before the death of Socrates. At the time of his own death he is
supposed to be a full-grown man. Allowing nine or ten years for the
interval between youth and manhood, the dialogue could not have been
written earlier than 390, when Plato was about thirty-nine years of age.
No more definite date is indicated by the engagement in which Theaetetus is
said to have fallen or to have been wounded, and which may have taken place
any time during the Corinthian war, between the years 390-387. The later
date which has been suggested, 369, when the Athenians and Lacedaemonians