Rudolf Carnap (1891–1970) is famous for his work on scientific verification. He received his Ph.D. from the University of Jena. He was a member of the Vienna Circle until he left Germany in 1935 to teach at the University of Chicago and the University of California at Los Angeles. In his early work he focused on the logical structure of language and what it implied about the world. In the 1940s, Carnap worked on logic and introduced the idea of a “state description,” which is the linguistic form of a possible world, or the most complete description of the world that can be given in any language.

Unlike earlier logical positivists, Carnap addressed the problem of inconclusive evidence for actual scientific verification and the meaning of scientific terms. He argued for the use of probability in determining “degrees of confirmation” in place of absolute verification. Carnap’s principle works include The Logical Structure of the World (1928; English translation, 1967), Philosophy and Logical Syntax (1935), Introduction to Semantics (1942), Formalization of Logic (1943), Meaning and Necessity: A Study in Semantics and Modal Logic (1947), and Logical Foundations of Probability (1950).