Rudolf Carnap (/ˈkɑːrnæp/;[20] German: [ˈkaʁnaːp]; 18 May 1891 – 14 September 1970) was a German-language philosopher who was active in Europe before 1935 and in the United States thereafter.

His mother came from an academic family; her father was an educational reformer and her oldest brother was the archaeologist Wilhelm Dörpfeld.

[5] While Carnap held moral and political opposition to World War I, he felt obligated to serve in the German army.

After three years of service, he was given permission to study physics at the University of Berlin, 1917–18, where Albert Einstein was a newly appointed professor.

Carnap then attended the University of Jena, where he wrote a thesis defining an axiomatic theory of space and time.

Frege's course exposed him to Bertrand Russell's work on logic and philosophy, which put a sense of the aims to his studies.

In 1924 and 1925, he attended seminars led by Edmund Husserl,[25] the founder of phenomenology, and continued to write on physics from a logical positivist perspective.

Carnap thereupon joined an informal group of Viennese intellectuals that came to be known as the Vienna Circle, directed largely by Schlick and including Hans Hahn, Friedrich Waismann, Otto Neurath, and Herbert Feigl, with occasional visits by Hahn's student Kurt Gödel.

He (with Hahn and Neurath) wrote the 1929 manifesto of the Circle, and (with Hans Reichenbach) initiated the philosophy journal Erkenntnis.

Thus began the lifelong mutual respect these two men shared, one that survived Quine's eventual forceful disagreements with a number of Carnap's philosophical conclusions.

Carnap, whose socialist and pacifist beliefs put him at risk in Nazi Germany, emigrated to the United States in 1935 and became a naturalized citizen in 1941.

During the late 1930s, Carnap offered an assistant position in philosophy to Carl Gustav Hempel, who accepted and became one of his most significant intellectual collaborators.

[27] Carnap (1963) later expressed some irritation about his time at Chicago, where he and Charles W. Morris were the only members of the department committed to the primacy of science and logic.

After a stint at the Institute for Advanced Study in Princeton (1952–1954), he joined the UCLA Department of Philosophy in 1954, Hans Reichenbach having died the previous year.

He had earlier refused an offer of a similar job at the University of California, Berkeley, because accepting that position required that he sign a loyalty oath, a practice to which he was opposed on principle.

[30] He was listed as a 'sponsor' for the "National Conference to Appeal the Walter-McCarran Law and Defend Its Victims" organised by the American Committee for the Protection of the Foreign Born,[31] and also for the "Scientific and Cultural Conference for World Peace" organised by the National Council of Arts, Sciences and Professions.

From 1919 to 1921, Carnap worked on a doctoral thesis called Der Raum: Ein Beitrag zur Wissenschaftslehre (Space: A Contribution to the Theory of Science, 1922).

In this dissertation on the philosophical foundations of geometry, Carnap tried to provide a logical basis for a theory of space and time in physics.

[33] That achievement has become a landmark in modern epistemology and can be read as a forceful statement of the philosophical thesis of logical positivism.

According to Carnap, philosophical propositions are statements about the language of science; they aren't true or false, but merely consist of definitions and conventions about the use of certain concepts.

Accordingly, the purpose of this constitutional system is to identify and discern different classes of scientific concepts and to specify the logical relations that link them.

In contrast, by analyzing the language and propositions of science, philosophers should define the logical foundations of scientific knowledge.

They include concepts like "god", "soul" and "the absolute" that transcend experience and cannot be traced back or connected to direct observations.

At that point in his career, Carnap attempted to develop a full theory of the logical structure of scientific language.

In fact, the basic function of these rules is to provide the principles to safeguard coherence, to avoid contradictions and to deduce justified conclusions.

Clearly enough, the principle of tolerance was a sophisticated device introduced by Carnap to dismiss any form of dogmatism in philosophy.

In fact, Carnap claims that the problem of induction is a matter of finding a precise explanation of the logical relation that holds between a hypothesis and the evidence that supports it.

In contrast, the probability of a statement about the degree of confirmation could be unknown, in the sense that one may miss the correct logical method to evaluate its exact value.

The most notable were: Herbert Feigl, Carl Gustav Hempel, Felix Kaufmann, Otto Neurath, and Moritz Schlick.

Some of the correspondence is considered notable and consist of his student notes, his seminars with Frege, (describing the Begriffsschrift and the logic in mathematics).