The bright and glorious period of Greek philosophy was from Socrates to Aristotle.  Philosophical inquiries began about the origin of things, and ended with an elaborate systematization of the forms of thought, which was the most magnificent triumph that the unaided intellect of man ever achieved.  Socrates does not found a school, nor elaborate a system.  He reveals most precious truths, and stimulates the youth who listen to his instructions by the doctrine that it is the duty of man to pursue a knowledge of himself, which is to be sought in that divine reason which dwells within him, and which also rules the world.  He believes in science; he loves truth for its own sake; he loves virtue, which consists in the knowledge of the good.

Plato seizes the weapons of his great master, and is imbued with his spirit.  He is full of hope for science and humanity.  With soaring boldness he directs his inquiries to futurity, dissatisfied with the present, and cherishing a fond hope of a better existence.  He speculates on God and the soul.  He is not much interested in physical phenomena; he does not, like Thales, strive to find out the beginning of all things, but the highest good, by which his immortal soul may be refreshed and prepared for the future life, in which he firmly believes.  The sensible is an impenetrable empire; but ideas are certitudes, and upon these he dwells with rapt and mystical enthusiasm,—­a great poetical rhapsodist, severe dialectician as he is, believing in truth and beauty and goodness.

Then Aristotle, following out the method of his teachers, attempts to exhaust experience, and directs his inquiries into the outward world of sense and observation, but all with the view of discovering from phenomena the unconditional truth, in which he too believes.  But everything in this world is fleeting and transitory, and therefore it is not easy to arrive at truth.  A cold doubt creeps into the experimental mind of Aristotle, with all his learning and his logic.

The Epicureans arise.  Misreading or corrupting the purer teaching of their founder, they place their hopes in sensual enjoyment.  They despair of truth.

But the world will not be abandoned to despair.  The Stoics rebuke the impiety which is blended with sensualism, and place their hopes on virtue.  Yet it is unattainable virtue, while their God is not a moral governor, but subject to necessity.

Thus did those old giants grope about, for they did not know the God who was revealed unto the more spiritual sense of Abraham, Moses, David, and Isaiah.  And yet with all their errors they were the greatest benefactors of the ancient world.  They gave dignity to intellectual inquiries, while by their lives they set examples of a pure morality.

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The Romans added absolutely nothing to the philosophy of the Greeks.  Nor were they much interested in any speculative inquiries.  It was only the ethical views of the old sages which had attraction or force to them.  They were too material to love pure subjective inquiries.  They had conquered the land; they disdained the empire of the air.