things and in men's thoughts about them,--the sad, self-conscious,
philosophy of Heraclitus, like one, knowing beyond his years, in this
barely adolescent world which he is so eager to instruct, makes no
pretence to be able to restrain that. Was not the very essence of
thought itself also such perpetual motion? a baffling transition from
the dead past, alive one moment since, to a present, itself deceased in
turn ere we can say, It is here? A keen analyst of the facts of nature
and mind, a master presumably of all the knowledge that then there was,
a vigorous definer of thoughts, he does but refer the superficial
movement of all persons and things around him to deeper and still more
masterful currents of universal change, stealthily withdrawing the
apparently solid earth itself from beneath one's feet. The principle
of disintegration, the incoherency of fire or flood (for Heraclitus
these are but very lively instances of movements, subtler yet more
wasteful still) are inherent in the primary elements alike of matter
and of the soul. Legei pou Herakleitos, says Socrates in the Cratylus,
hoti panta chorei kai ouden menei.+ But the principle of lapse, of
waste, was, in fact, in one's self. "No one has ever passed [16] twice
over the same stream." Nay, the passenger himself is without identity.
Upon the same stream at the same moment we do, and do not, embark: for
we are, and are not: eimen te kai ouk eimen.+ And this rapid change, if
it did not make all knowledge impossible, made it wholly relative, of a
kind, that is to say, valueless in the judgment of Plato. Man, the
individual, at this particular vanishing-point of time and place,
becomes "the measure of all things."

To know after what manner (says Socrates, after discussing the
question in what proportion names, fleeting names, contribute
to our knowledge of things) to know after what manner we must be
taught, or discover for ourselves, the things that really are