Logic

The Logical Syntax of Language

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Rudolf Carnap

1934

The Logical Syntax of Language (Logische Syntax der Sprache) marks Carnap's decisive turn from phenomenalist constructionism to the investigation of formal languages and their logical properties — a turn that defines his mature philosophy. Published in 1934, the work introduces the Principle of Tolerance: "In logic, there are no morals. Everyone is at liberty to build up his own logic, i.e., his own form of language, as he wishes." There is no single correct logical syntax; different formal systems (Carnap himself develops two, Languages I and II, with increasing expressive power) are equally legitimate, and philosophical disputes about which logic is "true" are pseudo-problems arising from the confusion of formal and factual questions. The distinction at the heart of the book is between the object language (in which we talk about the world) and the metalanguage (in which we talk about the logical properties of the object language) — a distinction Carnap uses to dissolve traditional metaphysical problems by showing that they arise from conflating syntactic talk-about-language with factual talk-about-the-world. Carnap introduces the concept of "material mode" versus "formal mode" of speech: to say "the world is made of numbers" (material mode) is to be confused; the proper formulation (formal mode) is "numerals are primitive signs in such-and-such a language." The Logical Syntax of Language established formal syntax as a core discipline of analytic philosophy and influenced Quine, Tarski, and the entire subsequent tradition of formal philosophy of language.