On May 18, 1891, German-born philosopher Rudolf Carnap was born. He was a major member of the Vienna Circle and an advocate of logical positivism and made significant contributions to logic and the philosophy of science. To avoid the ambiguities resulting from the use of ordinary language, he made a logical analysis of language. He believed in studying philosophical issues in artificial languages constructed under the rules of logic and mathematics, which he published in his famous books The Logical Structure of the World (1928) and The Logical Syntax of Language (1934).
“In science there are no ‘depths’; there is surface everywhere.”
— Rudolf Carnap (1929) from the Vienna Circle manifesto.
Rudolf Carnap – Early Years
Rudolf Carnap was born in Ronsdorf, near Düsseldorf, in the German Empire. His father had risen from the status of a poor ribbon-weaver to become the owner of a ribbon-making factory. His uncle was the archaeologist Wilhelm Dörpfeld, whom as a ten-year-old, Carnap accompanied on an expedition to Greece. After the Barmen Gymnasium, Carnap attended the University of Jena from 1910 to 1914, intending to write a thesis in physics. But he also studied carefully Kant’s Critique of Pure Reason during a course taught by Bruno Bauch, and was one of very few students to attend Gottlob Frege’s courses in mathematical logic, subsequently acknowledged as the greatest logician of the 19th century. Frege’s ideas exerted a deep influence on Carnap.
Surpass traditional Philosophy with logical Innovations
Then came World War I and Carnap 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 in 1917. Carnap then attended the University of Jena, where he wrote a thesis defining an axiomatic theory of space and time. The physics department said it was too philosophical, while the philosophy department said it was pure physics. Carnap then wrote another thesis on the theory of space in a more orthodox Kantian style, and published as Der Raum (Space) in 1922, where he makes the clear distinction between formal, physical and perceptual spaces. Frege’s course exposed Carnap to Bertrand Russell’s work on logic and philosophy. He accepted the effort to surpass traditional philosophy with logical innovations. In 1924, he attended seminars led by Edmund Husserl, the founder of phenomenology, and continued to write on physics from a logical positivist perspective.
“Philosophy is to be replaced by the logic of science — that is to say, by the logical analysis of the concepts and sentences of the sciences, for the logic of science is nothing other than the logical syntax of the language of science.”
— Rudolf Carnap, Logical Syntax of Language, 1934/1937
The Vienna Circle and the Logical Structure of the World
In 1926 Moritz Schlick, the founder of the Vienna Circle — a small group of philosophers, mathematicians, and other scholars who met regularly to discuss philosophical issues—invited Carnap to join the faculty of the University of Vienna, where he soon became an influential member of the Circle. In 1929, with Hans Hahn and Otto Neurath, Carnap wrote the manifesto of the Circle. In 1928, Carnap published The Logical Structure of the World, in which he developed a formal version of empiricism arguing that all scientific terms are definable by means of a phenomenalistic language. The great merit of the book was the rigor with which Carnap developed his theory. In the same year, he published Pseudoproblems in Philosophy, which asserted that many philosophical questions were meaningless, i.e., the way they were posed amounted to an abuse of language. An operational implication of this opinion was taken to be the elimination of metaphysics from responsible human discourse. This is the statement for which Carnap was best known for many years.
The following year, Carnap together with Hans Reichenbach founded the journal Erkenntnis. At the same time, Carnap met Alfred Tarski, who was developing his semantical theory of truth. Carnap was also interested in mathematical logic and wrote a manual of logic, entitled Abriss der Logistik (1929). As a result of many discussions with his associates in Vienna, Carnap soon began to develop a more liberal version of empiricism, which he further elaborated while he was professor of natural philosophy at the German University in Prague from 1931 to 1935. He eventually presented it in full detail in his essay Testability and Meaning, published in 1936. Carnap argued that the terms of empirical science are not fully definable in purely experiential terms but can at least be partly defined by means of “reduction sentences,” which are logically much-refined versions of operational definitions, and “observation sentences,” whose truth can be checked by direct observation.
Emigration to the USA
With the aid of the American philosophers Charles Morris and Willard Van Orman Quine, Carnap moved to the USA in 1936, where he became a professor at the University of Chicago. Although he was not Jewish, he had been vulnerable to persecution by the Nazis for his social-democratic political beliefs. He then spent two years at the Institute for Advanced Study at Princeton before taking an appointment at the University of California at Los Angeles.
“Science is a system of statements based on direct experience, and controlled by experimental verification. Verification in science is not, however, of single statements but of the entire system or a sub-system of such statements.”
— Rudolf Carnap, The unity of science, 1934
A Theory of Analycity
One idea in logic and the theory of knowledge that occupied much of Carnap’s attention was that of analyticity. In contrast to the 19th-century radical empiricism of John Stuart Mill, Carnap and other logical empiricists held that the statements of logic and mathematics, unlike those of empirical science, are analytic, i.e., true solely by virtue of the meanings of their constituent terms—and that they can therefore be established a priori (without any empirical test). Carnap repeatedly returned to the task of formulating a precise characterization and theory of analyticity.
While at UCLA, Carnap wrote on scientific knowledge, the analytic – synthetic dichotomy, and the verification principle. His writings on thermodynamics and on the foundations of probability and induction, were published posthumously. Carnap was working on the theory of inductive logic when he died on September 14, 1970, at Santa Monica, California. Carnap had a lasting influence on the development of analytical philosophy, which, however, in terms of content, began to detach itself from him, especially from the middle of the 20th century. The view that the task of philosophy consists essentially in the construction of artificial, logically stringent “scientific languages” was pushed back in favour of the analysis of normal colloquial language in the context of the linguistic turn.
Abraham Stone, Philosophy of Science: Carnap’s Aufbau, lecture 1, 
References and Further Reading:
-  Gottlob Frege and the Begriffsschrift, SciHi Blog
-  Rudolf Karnap at Internet Encyclopedia of Philosophy
-  Rudolf Carnap at Britannica Online
-  Homepage of the Collected Works of Rudolf Carnap. Department of Philosophy, Carnegie Mellon University
-  The time you enjoy wasting is not wasted time – Bertrand Russell, Logician and Pacifist, SciHi Blog
-  Edmund Husserl’s Phenomenology, SciHi Blog
-  Alfred Tarski and the Undefinability of Truth, SciHi Blog
-  Liberty vs. Authority according to John Stuart Mill, SciHi Blog
-  Works of and about Rudolf Carnap at the German Digital Library
-  Rudolf Carnap at Wikidata
-  Abraham Stone, Philosophy of Science: Carnap’s Aufbau, lecture 1, Abraham Stone @ youtube
-  Timeline for Rudolf Carnap, via Wikidata