Logical positivism is widely associated with an illiberal technocratic view of politics. This view is a caricature. Some members of the left Vienna circle were explicit in their criticism of this conception of politics. In particular, Neurath's work attempted to link the internal epistemological pluralism and tolerance of logical empiricism with political pluralism and the rejection of a technocratic politics. This paper examines the role that unified science played in Neurath's defence of political and social pluralism. Neurath's project of unified science addressed problems that lie at the centre of recent debates around liberalism concerning the possibility of social co-operation in conditions of pluralism. His response is distinctive in calling upon an empiricist tradition that differs from Kantian proceduralist approaches that have predominated in recent liberalism. While Neurath's position has problems, it deserves reconsideration, especially in so far as it questions the Kantian assumption that a thin language of abstract rights provides the best basis for the cosmopolital lingua franca required by conditions of social pluralism. An investigation of the role that unified science plays in Neurath's politics also gives reasons for revising common misconceptions about the nature of the unity of science programme itself. © 2003 Published by Elsevier Ltd.