of his own mind; and he cannot escape from the further accident of being
dependent for his knowledge on others. But still this is no reason why he
should always be in doubt; of many personal, of many historical and
scientific facts he may be absolutely assured. And having such a mass of
acknowledged truth in the mathematical and physical, not to speak of the
moral sciences, the moderns have certainly no reason to acquiesce in the
statement that truth is appearance only, or that there is no difference
between appearance and truth.

The relativity of knowledge is a truism to us, but was a great
psychological discovery in the fifth century before Christ. Of this
discovery, the first distinct assertion is contained in the thesis of
Protagoras. Probably he had no intention either of denying or affirming an
objective standard of truth. He did not consider whether man in the higher
or man in the lower sense was a 'measure of all things.' Like other great
thinkers, he was absorbed with one idea, and that idea was the absoluteness
of perception. Like Socrates, he seemed to see that philosophy must be
brought back from 'nature' to 'truth,' from the world to man. But he did
not stop to analyze whether he meant 'man' in the concrete or man in the
abstract, any man or some men, 'quod semper quod ubique' or individual
private judgment. Such an analysis lay beyond his sphere of thought; the
age before Socrates had not arrived at these distinctions. Like the
Cynics, again, he discarded knowledge in any higher sense than perception.
For 'truer' or 'wiser' he substituted the word 'better,' and is not
unwilling to admit that both states and individuals are capable of
practical improvement. But this improvement does not arise from
intellectual enlightenment, nor yet from the exertion of the will, but from
a change of circumstances and impressions; and he who can effect this
change in himself or others may be deemed a philosopher. In the mode of
effecting it, while agreeing with Socrates and the Cynics in the importance