Rudolf Carnap is undoubtedly one of the central figures in twentieth-century scientific philosophy. While his work covers a wide spectrum of topics in philosophy of logic and mathematics, philosophy of language, formal philosophy of science, and probability theory (among other fields), a particular method of doing philosophy can be identified in all of his contributions. This is the use of formal logic in his approach to philosophical problems. Logic plays an essential role in Carnap’s work throughout his intellectual career, from his early type-theoretic formulation of a constitution theory of knowledge in Der logische Aufbau der Welt (Carnap 1928) to his mature work on a theory of probability, e.g. (Carnap 1950).