The American philosopher Rudolf Carnap (1891-1970) was the most prominent representative of the school of logical positivism, sometimes called logical empiricism.

Rudolf Carnap was born on May 18, 1891, in Ronsdorf, Germany. From 1910 to 1914 he studied philosophy and science at the universities of Jena and Freiburg. At Jena, Gottlob Frege, the pioneering mathematical logician, directed his thinking. Carnap served as an officer in the Germany army during World War I, later resuming his studies at Jena, where he received his doctorate in 1921. As a student, Carnap came under the influence of Bertrand Russell and his writings on logic and epistemology.

In 1923 Carnap met Hans Reichenbach, with whom he later founded and edited Erkenntnis (1930-1940), the journal of the logical empiricists. Through Reichenbach he met Moritz Schlick, head of the Philosophical Circle at the University of Vienna. In 1926 Carnap became instructor of philosophy there and participated in the Circle. Ludwig Wittgenstein attended meetings of the Circle in 1927, becoming another influence on Carnap's thought.

Carnap won wide recognition among philosophers with the publication of the Logische Aufbau der Welt (Logical Structure of the World) in 1928. He offered a new methodology, which called for the reduction of all knowledge to private, subjective sense-data in order to construct a technical system to embrace all known-objects and to solve philosophical problems. In 1928 Carnap also published Scheinprobleme in der Philosophie (Fictitious Problems in Philosophy). Following Wittgenstein, he sought to show that metaphysical problems are pseudoproblems and that metaphysical sentences are "non-sense."

In 1931 Carnap became professor of natural philosophy at the German university in Prague. In 1933 he married Elizabeth Ina von Stöger.

Carnap's investigations into logic and mathematics came to fruition with the publication of The Logical Syntax of Language (1934). Utilizing the distinction between "metalanguage" and "object language" advanced by Polish logicians, Carnap sought to develop a metalanguage (which he called "logical syntax") to elucidate and formalize the basic terms, formation rules, and transformation rules of object languages--that is, systems of logic and mathematics. He proposed his famous "principle of tolerance," which permits anyone to construct any language he wishes.

Fleeing from Nazism, Carnap went to the United States in December 1935. A few months later he was appointed professor of philosophy at the University of Chicago. In 1941 he became a naturalized citizen. Except for leaves to research or to teach elsewhere, he remained at Chicago until 1952.

At the university Carnap joined Otto Neurath and Charles W. Morris to found and edit the International Encyclopedia of Unified Science. Carnap's contribution to the encyclopedia is entitled Foundations of Logic and Mathematics (1930). This work displays a radical shift in his thinking. Persuaded by Alfred Tarski, Carnap had become convinced that the logical analysis of language extends beyond logical syntax and includes semantics, which deals with the reference of language to objects and contains the concepts of meaning and truth. Thus Carnap initiated a series of studies in semantics: Introduction to Semantics (1942), Formalization of Logic (1943), and Meaning and Necessity (1947).

In 1950 Carnap's massive book, The Logical Foundations of Probability, climaxed his investigations into the logic of empirical knowledge. From 1952 to 1954 Carnap advanced his researches into the logic of science at the Institute for Advanced Study in Princeton. In 1954 he accepted the chair in philosophy at the University of California, Los Angeles, made vacant by the death of Reichenbach. Retiring from teaching in 1961, he continued as a research professor until his death on Sept. 14, 1970, in Santa Monica, Calif.

Further Reading

• P. A. Schillp, ed., The Philosophy of Rudolf Carnap (1963), containing Carnap's intellectual autobiography, is basic. Carnap's views receive some attention in Julian Weinberg, An Examination of Logical Positivism (1936); Victor Kraft, The Vienna Circle (1950); and Joergen Joergensens, The Development of Logical Positivism (1951). See also Wolfgang Stegmuller, Die Wahrheitsidee und die Idee der Semantik (1957); B. H. Kazemeir and D. Vuijsje, eds., Logic and Language (1962); Alan Hausman and Fred Wilson, Carnap and Goodman (1967); and Arne Naess, Four Modern Philosophers.