"Pre-Socratic" is the term commonly used (and the one that will be used here) to cover those Greek thinkers from approximately 600 to 400 BCE who attempted to find universal principles that would explain the whole of nature, from the origin and ultimate constituents of the universe to the place of man within it. Yet 400 was the last year of Socrates' life, and among the Sophists, who are also excluded, Protagoras and Gorgias were older than he and others were his contemporaries. "Pre-Socratic" therefore indicates not so much a chronological limit as an outlook and a range of interests. This outlook Protagoras and Socrates deliberately attacked, condemning natural philosophy as worthless compared with the search for a good life, the discussion of social and political questions, and individual morality. Socrates also dismissed its explanations as inadequate because expressed predominantly in terms of origins and internal mechanisms. In his...