The daring idea that convention - human decision - lies at the root both of necessary truths and much of empirical science reverberates through twentieth-century philosophy, constituting a revolution comparable to Kant's Copernican revolution. This is the first comprehensive study of Conventionalism. Drawing a distinction between two conventionalist theses, the under-determination of science by empirical fact, and the linguistic account of necessity, Yemima Ben-Menahem traces the evolution of both ideas to their origins in Poincare's geometric conventionalism. She argues that the radical extrapolations of Poincare's ideas by later thinkers, including Wittgenstein, Quine, and Carnap, eventually led to the decline of conventionalism. This book provides a new perspective on twentieth-century philosophy. Many of the major themes of contemporary philosophy emerge in this book as arising from engagement with the challenge of conventionalism.

1. Overview: the varieties of conventionalism; 2. Origins: Poincaré and Duhem and convention; 3. Relativity: from 'experience and geometry' to 'geometry and experience'; 4. Implicit definition; 5. 'Unlimited possibilities': Carnap on convention; 6. Metaphor and argument: Quine on convention; 7. Wittgenstein: from conventionalism to Iconoclasm.