German logical positivist. Carnap left Vienna to become professor at Prague in 1931, and fled Nazism to become professor in Chicago in 1935. He subsequently worked at Los Angeles from 1952 to 1961. Carnap was probably more influential than any other thinker in combining a basic empiricism with the logical tools provided by Frege and Russell, and it is in his works that the main achievements (and difficulties) of logical positivism are best exhibited. His first major work was Der logische Aufbau der Welt (1928, trs. as The Logical Structure of the World, 1967). This phenomenalistic work attempts a reduction of all the objects of knowledge, by generating equivalence classes of sensations, related by a primitive relation of remembrance of similarity. This is the solipsistic basis of the construction of the external world, although Carnap later resisted the apparent metaphysical priority here given to experience. His hostility to metaphysics soon developed into the characteristic positivist view that metaphysical questions are pseudo-problems. Criticism from Neurath shifted Carnap’s interest towards a view of the unity of the sciences, with the concepts and theses of special sciences translatable into a basic physical vocabulary whose protocol statements describe not experience but the qualities of points in space-time. Carnap pursued the enterprise of clarifying the structures of mathematical and scientific language (the only legitimate task for scientific philosophy) in Logische Syntax der Sprache (1934, trs. as The Logical Syntax of Language, 1937). Refinements to his syntactic and semantic views continued with Meaning and Necessity (1947), while a general loosening of the original ideal of reduction culminated in the great Logical Foundations of Probability, the most important single work of confirmation theory, in 1950. Other works concern the structure of physics and the concept of entropy.

Throughout his work Carnap continued his hostility to metaphysics, believing that questions such as whether numbers exist merely raise a choice, that can be settled either way, of the framework of description that we are to adopt. Frameworks themselves are to be valued according to their utility. Because his views are both forthright and developed Carnap has been a convenient target for critics of the structures that positivism tended to impose upon linguistic and scientific thought. However, his massive range and insistence on precision in philosophy have made him one of the 20th century’s most influential philosophers.