What is justice? Is the life upheld by Socrates sufficiently definite for practical guidance? The views of Callicles have been overborne; but have they been thoroughly examined? Socrates claims to be the only politician. But how can that deserve the name of policy which results in doing nothing? These and cognate questions may well have haunted Plato when he planned the Republic, the greatest of his works. The great principle of the political supremacy of mind, though thus held back through half the dialogue, really dominates the whole. It may be read between the lines all through, even in the institution of gymnastic and the appraisement of the cardinal virtues. It is a genuine development of Socratic thought. And it is this more than any other single feature which gives the Republic a prophetic significance as an attempt towards anticipating the work of future generations.