This book offers an introduction to the Sophists of fifth-century Athens and a new overall interpretation of their thought. Since Plato first animadverted on their activities, the Sophists have commonly been presented as little better than intellectual mountebanks - a picture which Professor Kerferd forcefully challenges here. Interpreting the evidence with care, he shows them to have been part of an exciting and historically crucial intellectual movement. At the centre of their teaching was a form of relativism, most famously expressed by Protagoras as 'Man is the measure of all things', and which they developed in a wide range of views - on kwledge and argument, virtue, government, society, and the gods. On all these subjects the Sophists did far more than simply provoke Plato to thought. Their contributions were substantial and serious; they inaugurated the debate on many central philosophical questions and decisively shifted the focus of philosophical attention from the cosmos to man.