ity of knowledge on the Heraclitean flux? (c) Would he have
asserted the absoluteness of sensation at each instant? Of the work of
Protagoras on 'Truth' we know nothing, with the exception of the two
famous fragments, which are cited in this dialogue, 'Man is the measure
of all things,' and, 'Whether there are gods or not, I cannot tell.' Nor
have we any other trustworthy evidence of the tenets of Protagoras, or
of the sense in which his words are used. For later writers, including
Aristotle in his Metaphysics, have mixed up the Protagoras of Plato, as
they have the Socrates of Plato, with the real person.

Returning then to the Theaetetus, as the only possible source from which
an answer to these questions can be obtained, we may remark, that Plato
had 'The Truth' of Protagoras before him, and frequently refers to the
book. He seems to say expressly, that in this work the doctrine of the
Heraclitean flux was not to be found; 'he told the real truth' (not
in the book, which is so entitled, but) 'privately to his
disciples,'--words which imply that the connexion between the doctrines
of Protagoras and Heracleitus was not generally recognized in Greece,
but was really discovered or invented by Plato. On the other hand,
the doctrine that 'Man is the measure of all things,' is expressly
identified by Socrates with the other statement, that 'What appears to
each man is to him;' and a reference is made to the books in which the
statement occurs;--this Theaetetus, who has 'often read the books,' is
supposed to acknowledge (so Cratylus). And Protagoras, in the speech
attributed to him, never says that he has been misunderstood: he rather
seems to imply that the absoluteness of sensation at each instant was
to be found in his words. He is only indignant at the 'reductio ad
absurdum' devised by Socrates for his 'homo mensura,' which Theodorus
also considers to be 'really too bad.'

The question may be raised, how far Plato in the Theaetetus could
have misrepresented Protagoras without violating the laws of dramatic
probability. Could he have pretended to cite from a well-known writing
what was not to be found there? But such a shadowy enquiry is not worth
pursuing further. We need only remember that in the criticism which
follows of the thesis of Protagoras, we are criticizing the Protagoras
of Plato, and not attempting to draw a precise line between his real
sentiments and those which Plato has attributed to him.

2. The other