y amusing himself by giving
oracles out of the shrine of his book."[167:13]

This is the full swing of the pendulum from _dogmatism_, or the
uncritical conviction of truth. A modified form of scepticism has been
developed in these later days under the influence of natural science,
and is called _agnosticism_ or _positivism_. It accepts the Protagorean
doctrine only in the sense of attributing to human knowledge as a whole
an incapacity for exceeding the range of perception. Beyond this realm
of natural science, where theories can be sensibly verified, lies the
unknowable realm, more real, but forever inaccessible.

[Sidenote: The Source and Criterion of Knowledge According to Empiricism
and Rationalism. Mysticism.]

Sect. 68. It is important to note that both scepticism and agnosticism
agree in regarding _perception as the essential factor in knowledge_. So
far at any rate as our knowledge is concerned, the certification of
being consists in perceivability. Knowledge is coextensive with actual
and possible human experience. This account of the source and criterion
of knowledge is called _empiricism_, in distinction from the
counter-theory of _rationalism_.

The rationalistic motive was a quickening influence in Greek philosophy
long before it became deliberate and conspicuous in Socrates and Plato.
Parmenides, founder of the Eleatic School, has left behind him a poem
divided into two parts: "The Way of Truth" and "The Way of
Opinion."[168:14] In the first of these he expounds his esoteric
philosophy, which is a definition of being established by dialectical
reasoning. He finds that being must be single, eternal, and changeless,
because otherwise it cannot be thought and defined without
contradiction. The method which Parmenides here employs presupposes that
knowledge consists in understanding rather than perception. Indeed, he
regards the fact that the world of the senses is manifold and mutable as
of little consequence to the wise man. The world of sense is the
province of vulgar opinion, while that of reason is the absolute truth
revealed only to the philosopher. The truth has no concern with
appearance, but is answerable only to the test of rationality. _That
world is real which one is able by thinking to make intelligible._ The
world is what a world must be in order to be possible at all, and the
philosopher can deduce it directly from the very conditions of thought
which it must satisfy. He who would know