IN BOOK VII OF THE REPUBLIC, the Greek philosopher Plato recounts a dialogue between his younger brother, Glaucon, and his teacher, Socrates. The dialogue is an allegory about a cave. It is the duty of the philosopher, Socrates says, to lead us all from the darkness of the cave, with its false understandings built only on shadows and echoes, into the sunshine, where we will finally see the truth. In the light of true knowledge and reason, humans will at last come into our own. This, anyway, is what Socrates argues.