German-born US philosopher and a leading logical positivist.
Carnap was educated at the universities of Freiburg and Jena, where he studied under Frege. In 1926 he moved to Vienna and joined the influential group of philosophers led by Schlick and known as the Vienna Circle. Carnap was one of its most influential members, and in 1930 he and Hans Reichenbach (1913–67) founded and edited the important philosophical journal Erkenntnis. In 1931 he was appointed to the chair of philosophy at Prague, but in 1935 he left Europe for the USA, where he served as professor of philosophy, first at the University of Chicago and from 1954 until his retirement in 1961 at the University of California, Los Angeles.
As a radical positivist Carnap's first major work was Der logische Aufbau der Welt (1928; translated as The Logical Structure of the World, 1967). In it he sought to construct the world of experience, using the primitive relation of ‘recognition of similarity’. In a later work, The Logical Syntax of Language (1934), he proposed his famous principle of tolerance and also introduced into philosophy the important distinction between the formal and material modes of speech. Failure to distinguish between them clearly, he declared, was a common cause of philosophical confusion.
Carnap was quick to see that such purely syntactical approaches were inadequate, and in his Introduction to Semantics (1942) and other works of the 1940s he began to insist that such formal concepts as ‘implication’ and ‘analyticity’ could only be analysed semantically. Later he turned his attention to problems in the philosophy of science. In his most significant work, The Logical Foundations of Probability (1950), he argued that there were in fact two concepts of probability. The simplest could be defined in terms of relative frequency. The other, more ambitiously, he identified as the degree of confirmation assigned to a particular hypothesis on the basis of supporting evidence. This relation, he insisted, was a logical relation, weaker than but similar to the more familiar notion of logical implication. Carnap was in reality attempting to develop a new formal inductive logic. Despite his own labours of twenty years, and a further decade's work by numerous logicians, it is still far from clear whether or not Carnap's project is a viable one.