s, between ignorance and
knowledge, ascribing to it a certain measure of truth, and making it
the starting-point for reflection. And further, he transforms the
Socratic idea of morality, rejecting the notion that its principle is
to be found in a mere calculation of pleasures, {38} and maintaining
that particular goods must be estimated by the good of life as a whole.
Plato's philosophy rests upon his doctrine of ideas, which, as the
types of permanent reality, represent the eternal nature of things; and
the problem of life is to rise from opinion to truth, from appearance
to reality, and attain to the ideal principle of unity. The highest
good Plato identifies with God, and man's end is ultimately to be found
in the knowledge of, and communion with, the eternal.

The human soul he conceived to be a mixture of two elements. In virtue
of its higher spiritual nature it participates in the world of ideas,
the life of God: and in virtue of its lower or animal impulses, in the
corporeal world of decay. These two dissimilar parts are connected by
an intermediate element called by Plato _thymos_ or courage, implying
the emotions or affections of the heart. Hence a threefold
constitution of the soul is conceived--the rational powers, the
emotional desires, and the animal passions. If we ask who is the good
man? Plato answers, it is the man in whom these three elements are
harmonised. On the basis of this psychology Plato classifies and
determines the virtues--adopting the four cardinal virtues of Greek
tradition as the fundamental types of morality. Wisdom is the quality,
or condition of all virtue and the crown of the moral life: courage is
the virtue of the emotional part of man; temperance or moderation, the
virtue of the lower appetites: while justice is the unity and the
principle of the others. Virtue is thus no longer identified with
knowledge simply. Another source of vice besides ignorance is assumed,
viz., the disorder and conflict of the soul; and the well-being of man
lies in the attainment of a well-ordered and harmonious life. As
health is the harmony of the body, so virtue is the harmony of the
soul--a condition of perfection in which every desire is kept in
control and every function performs its part with a view to the good of
the whole. Morality, however, does not belong merely to the
individual, but has its perfect realisation in the state in which the
three elements of the soul have their {39} co