In this book, Zilioli relates Protagoras' relativism with modern forms of relativism, in particular the 'robust relativism' of Joseph Margolis. He also gives an integrated account both of the perceptual relativism examined in Plato's Theatetus and the ethical or social relativism presented in the first part of Plato's Protagoras and offers an integrated and positive analysis of Protagoras' thought, rather than focusing on ancient criticisms and responses to his thought. This is a deeply scholarly work which brings much argument to bear to the claim that Protagoras was and remains Plato's subtlest philosophical enemy.