The concept sensus communis-a term that means a great deal more than its English translation "common sense"-has served as a key principle in the theory of knowledge from the ancient Greeks through the Enlightenment philosophers. John D. Schaeffer shows how the seventeenth-century Italian philosopher Giambattista Vico synthesized Greek and Roman ideas of what sensus communis and what this synthesis implies for current discussions of rhetoric and hermeneutics. Arguments for ethical relativism emerge from divisions between sensus communis as an ethical judgment (a concept that Richard Rorty, Richard Bernstein, and others have tried to rescue) and as a linguistic consensus, a division against which Vico argued and which his own concept of sensus communis attempted to reconcile. In extended commentaries on Gadamer, the Gadamer/Habermas debate, and Derrida, Schaeffer shows that Vico offers the possibility of analyzing social phenomena and constellations of power from within the humanist rhetorical tradition. Vico's achievements have powerful implications for relating ethics and hermeneutics to the world of concrete social practice, particularly in an age in which the electronic media have replaced print as the primary means of communication and in which a "secondary orality" (a cast of mind similar to that of nonliterate peoples) is appearing within our literate civilization.