s, is there nothing that is immutable and
permanent? Have we no ultimate standard of Right? Is there no criterion
of Truth? Plato believed most confidently there was such a criterion and
standard. He had learned from Socrates, his master, to cherish an
unwavering faith in the existence of an Eternal Truth, an Eternal Order,
an Eternal Good, the knowledge of which is essential to the perfection
and happiness of man, and which knowledge must therefore be presumed to
be attainable by man. Henceforth, therefore, the ceaseless effort of
Plato's life is to attain a standard (kriterion)[506]--a CRITERION OF
TRUTH.

[Footnote 506: "Theaetetus," Sec. 89.]

At the outset of his philosophic studies, Plato had derived from
Socrates an important principle, which became the guide of all his
subsequent inquiries. He had learned from him that the criterion of
truth must be no longer sought amid the ever-changing phenomena of the
"sensible world." This had been attempted by the philosophers of the
Ionian school, and ended in failure and defeat. It must therefore be
sought in the metaphenomenal--the "intelligible world;" that is, it must
be sought in the apperceptions of the reason, and not in opinions
founded on sensation. In other words, he must look _within_. Here, by
reflection, he could recognize, dimly and imperfectly at first, but
increasing gradually in clearness and distinctness, two classes of
cognitions, having essentially distinct and opposite characteristics. He
found one class that was complex (synkegumenon), changeable (thateron),
contingent and relative (ta pros ti schesin echonta); the other, simple
(kexorismenon), unchangeable (akineton), constant (tauton), permanent
(to on aei), and absolute (anypotheton = aploun). One class that may be
questioned, the other admitting of no question, because self-evident and
necessary, and therefore compelling belief. One class grounded on
sense-perception, the other conceived by reason alone. But whilst the
reason recognizes, it does not create them. They are not particular and
individual, but universal. They belong not to the man, but to the race.

He found, then, that there are in all minds certain "principles" which
are fundamental--principles which lie at the basis of all our cognitions
of the objective world, and which, as "mental laws," determine all our
forms of thought; and principles, too, which have this marvellous and
undeniable character, that they are encountered in the