This book recounts the hitherto untold story of conventionalism. The profound impact conventionalism has had on seminal developments in both the science and the philosophy of the twentieth century is revealed through analysis of the writings of Poincaré, Duhem, Carnap, Wittgenstein, and Quine on the subject, and by examining the debate over conventionalism in the context of the theory of relativity and the foundations of mathematics. I trace the evolution of conventionalism from Poincaré's modest but precise initial conception through a number of extravagant extrapolations, all of which, I show, eventually collapsed under the weight of the problems they generated. My focus, however, is not history but analysis. The literature is replete with ambiguity as to what the meaning of ‘convention’ is, misunderstandings about the aims of conventionalism, and conflation of conventionalism with other philosophical positions, such as instrumentalism and relativism. The most serious confusion pertains to the notion of truth by convention typically associated with conventionalism. A central theme of this book is that conventionalism does not purport to base truth on convention, but rather, seeks to forestall the conflation of truth and convention.

Much of twentieth-century philosophy was characterized by engagement in determining the limits of meaning and countering the tendency to ascribe meaning to meaningless expressions. Conventionalism, correctly understood, is motivated by a desire to mitigate deceptive ascription of truth. To the conventionalist, the very idea of truth by convention is as incongruous as that of meaningful nonsense.