d rectitude of purpose, that longing after truth,
that inward sympathy with, and reverence for justice, and purity, and
goodness, which dwelt in the heart of Socrates, and which constrained
him to believe in their reality and permanence. He could not endure the
thought that all ideas of right were arbitrary and factitious, that all
knowledge was unreal, that truth was a delusion, and certainty a dream.
The world of sense might be fleeting and delusive, but the voice of
reason and conscience would not mislead the upright man. The opinions of
individual men might vary, but the universal consciousness of the race
could not prevaricate. However conflicting the opinions of men
concerning beautiful things, right actions, and good sentiments, Plato
was persuaded there are ideas of Order, and Right, and Good, which are
universal, unchangeable, and eternal. Untruth, injustice, and wrong may
endure for a day or two, perhaps for a century or two, but they can not
always last; they must perish. The _just_ thing and the _true_ thing are
the only enduring things; these are eternal. Plato had a sublime
conviction that his mission was to draw the Athenian mind away from the
fleeting, the transitory, and the uncertain, and lead them to the
contemplation of an Eternal Truth, an Eternal Justice, an Eternal
Beauty, all proceeding from and united in an Eternal Being--the ultimate
agathon--_the Supremely Good_. The knowledge of this "Supreme Good" he
regarded as the highest science.[490]

[Footnote 490: "Republic," bk. vi. ch. xvi. p. 193.]

Added to these moral qualifications, Plato had the further qualification
of a comprehensive knowledge of all that had been achieved by his
predecessors. In this regard he had enjoyed advantages superior to those
of Socrates. Socrates was deficient in erudition, properly so called. He
had studied men rather than books. His wisdom consisted in an extensive
_observation_, the results of which he had generalized with more or less
accuracy. A complete philosophic method demands not only a knowledge of
contemporaneous opinions and modes of thought, but also a knowledge of
the succession and development of thought in past ages. Its instrument
is not simply psychological analysis, but also historical analysis as a
counterproof.[491] And this erudition Plato supplied. He studied
carefully the doctrines of the Ionian, Italian, and Eleatic schools.
Cratylus gave him special instruction in the theories of
Heraclitu