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The Linguistic Turn: Rudolph Carnap
Logical syntax provides the conventional rules that set out the forms of any meaningful proposition erman positivist philosopher and leading member of the ‘Vienna Circle’, Carnap was a dominant figure in the development of postWar philosophy in the USA. A student of Frege at Jena, he went on to Vienna and became heavily influenced by the work of both Russell and Wittgenstein. However, with the rise of National Socialism he left Europe for America, where he remained for the rest of his life. The corpus of his work consists of over 20 books and some 80 articles which together have made major contributions to logic, semantics and the philosophy of science. The most important of these are The Logical Structure of the World and The Logical Syntax of Language. Along with Schlick and Carl Hempel, Carnap was a strong proponent of the verification principle. For Carnap, this principle meant that anything that might count as a contribution to human knowledge can either be justified by observation and experience or is merely formal and expressed in tautological propositions. Carnap’s best contribution to this idea was his meticulous working out of the nature of these formal, tautological propositions, which he described as the ‘logical syntax of the language of science’. This logical syntax, Carnap held, provides the conventional rules that set out the possible forms of any meaningful proposition. In the past, philosophers have mistaken such rules for substantive philosophical claims, but a proper understanding of their nature shows them to be what Wittgenstein would later call ‘norms of representation’. For instance, the claim ‘time extends infinitely in both directions’ can be
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shown to be nothing more than the ‘syntactic’ proposition that any positive or negative real number can be used to represent a timecoordinate. Such a proposition possesses no empirical or cognitive content, but rather expresses a rule for the use of signs. Carnap believed that the logical syntax of science could be laid bare by a thorough investigation into all the possible forms of a proposition, in other words into the structural relationships between all the signs in a language. This, Carnap held, should be the task of philosophy, making philosophy purely the business of linguistic analysis. At this point in his work Carnap was convinced that the syntactic investigation into the possible combination of signs, logical syntax, could not have any connection with what those signs were actually used to represent. In other words, logical syntax and empirical content were two distinct and unrelated studies. The first belongs to philosophy, the second to the various branches of science. Under the influence of Gödel and Tarski, however, Carnap was forced to revise this position. It became clear that some philosophically important properties of language could not be reduced to syntactic structures, in particular the property of truth, which required a semantic analysis. Since Tarski had shown that it was possible to develop a formal theory of semantics using a meta-language referring to an object language, Carnap now set about defining semantic rules, or definitions, for a theory of truth. To this branch of logical analysis he made significant contributions which would heavily influence his student and disciple, W.V.O.Quine.
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