permanent essence or
being to be found. Hence Protagoras inferred that truth must vary with
the ever-varying sensations of the individual. "Man (the individual) is
the measure of all things." Knowledge is a purely relative thing, and
every man's opinion is truth for him.[500] The law of right, as
exemplified in the dominion of a party, is the law of the strongest;
fluctuating with the accidents of power, and never attaining a permanent
being. "Whatever a city enacts as appearing just to itself, this also is
just to the city that enacts it, so long as it continues in force."[501]
"The just, then, is nothing else but that which is expedient for the
strongest."[502]

[Footnote 498: "Theaetetus," Sec. 23.]

[Footnote 499: Ibid., Secs. 25, 26.]

[Footnote 500: Ibid., Secs. 39, 87.]

[Footnote 501: Ibid., Sec. 87.]

[Footnote 502: "Republic," bk. i. ch. xii.]

2. The second theory is that which denies the existence (except as
phantasms, images, or mere illusions of the mind) of the whole of
sensible phenomena, and refers all knowledge to the _rational
apperception of unity_ (to en) _or the One_.

This was the doctrine of the later Eleatics. The world of sense was, to
Parmenides and Zeno, a blank negation, the _non ens_. The identity of
thought and existence was the fundamental principle of their philosophy.

"Thought is the same thing as the cause of thought; For
without the thing in which it is announced, You can not find
the thought; for there is nothing, nor shall be, Except the
existing."[503]

[Footnote 503: Parmenides, quoted in Lewes's "Biog. History of
Philosophy," p. 54.]

This theory, therefore, denied to man any valid knowledge of the
external world.

It will at once be apparent to the intelligent reader that the direct
and natural result of both these theories[504] of knowledge was a
tendency to universal skepticism. A spirit of utter indifference to
truth and righteousness was the prevailing spirit of Athenian society.
That spirit is strikingly exhibited in the speech of Callicles, "the
shrewd man of the world," in "Gorgias" (Sec.85, 86). Is this new to our
ears?" My dear Socrates, you talk of _law_. Now the laws, in my
judgment, are just the work of the weakest and most numerous; in framing
them they never thought but of themselves and their own interests; they
never approve or censure except in reference to _this._ Hence it is that
the cant arises that tyranny is improper