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Summary Article: Carnap, Rudolf
From Blackwell Companions to Philosophy: A Companion to Metaphysics

(1891–1970) A leading German logical positivist (see logical positivism). At university. Carnap studied both physics and philosophy. From 1925–36, he was an important participant in the Vienna Circle. In 1936 Carnap emigrated to the United States, where his work in philosophy of science, philosophy of language, modal logic and inductive logic shaped and promoted the absorption of logical positivist ideas into the American philosophical mainstream. In his autobiography (in Schilpp, 1963, p. 45), Carnap laments the vague, inconclusive character of traditional metaphysics: “most of the controversies in traditional metaphysics appeared to me sterile and useless … I was depressed by disputations in which the opponents talked at cross purposes; there seemed hardly any change of mutual understanding, let alone of agreement, because there was not even a common criterion for deciding the controversy.” This anti-metaphysical animus informs Carnap's two most important books, Der logische Aufbau der Welt (1928) and Logische Syntax der Sprache (1934). In both these works Carnap proposes to replace philosophy with a successor discipline devoted to the application of modern logic to the clarification of the concepts of science.

In Der logische Aufbau der Welt Carnap advocates the development of constitution systems as the successor to philosophy. A constitution system is an ordered system or definitions of scientific concepts. Constitution systems are to be comprehensive, embracing all the concepts of all the formal and empirical sciences. By “definition”, Carnap means explicit definition. Carnap assumes, in effect, a version of the simple theory of types as the background language and logic for constitution systems; and he takes Whitehead and Russell to have demonstrated that mathematics can be unproblematically developed in this framework. Each constitution system has a basis: a domain of individuals and primitive relations over the domain. Carnap believes that there are alternative bases for constitution systems, and hence distinct, though equivalent, systems; he holds forth the prospect of systems with a physical basis of fundamental particles and fundamental magnitudes. However, to illustrate constitution systems, Carnap sketches the development of an epistemologically oriented system with an autopsychological basis: the individuals are the total momentary experiences of a person; the single undefined relation is that of recollected similarity. The order of definition in this system is to reflect epistemological priority in the application of concepts.

A constitution system contains definitions for the concepts employed by the existing formal and empirical sciences. Carnap relies on this feature of these systems to motivate his claim that any rational statement can be formulated within a constructional system. Statements drawing on concepts not so definable are non-rational. Carnap believes his autopsychological constitution system expresses the core common to various epistemological positions, capturing the insights each emphasizes. This achievement makes evident that these epistemological positions differ only in their non-rational, metaphysical assertions. So, Carnap holds that his sample system captures the Kantian insight that objective knowledge requires the synthesis of something given to the form of the unity of the object (see kant). However, for Carnap, synthesis is not understood in terms of an ordering that a transcendental subject imposes on a given manifold in accordance with the immutably valid forms of thought, as neo-Kantians held (see transcendental ego). Instead, type theory replaces transcendental logic; formal definitions replace synthesis. Talk of transcendental subjects as well as unconceptualizable things-in-themselves disappears (see noumenal/phenomenal). Similarly, in defining scientific concepts from an autopsychological basis, this constitution system captures the Machian empiricist insight that all empirical knowledge arises from experience, that every scientific statement is reducible to an equivalent one concerning elementary experiences (see empiricism; mach). But this reducibility does not in any way ontologically privilege the elementary experiences over objects defined at later stages of the system.

In Logische Syntax der Sprache Carnap urges that philosophy be replaced by the logic of science, by the logical syntax of languages for science. Central to Carnap's view of logical syntax is his notion of a language or linguistic framework, a notion that, with modifications, Carnap held for the rest of his career. Languages are to be described in purely formal terms via formation rules defining sentencehood and transformation rules defining a consequence relation for the language. The logical pluralism voiced in Carnap's Principle of Tolerance gives logical syntax its significance: “In logic, there are no morals. Everyone is at liberty to build up his own logic … All that is required of him is that … he must state his methods clearly, and give syntactical rules instead of philosophical arguments” (Carnap, 1934, p. 52). In denying that there is a right or wrong in logic, Carnap rejects any framework transcendent notion of fact or truth. He accordingly comes to distinguish sharply between the decision to adopt a linguistic framework and the epistemic evaluation of sentences of a particular framework. The former is a matter of practical decision, ultimately of preference. The latter evaluations are constrained by the defining rules of a particular language.

Carnap adopts the Principle of Tolerance in response to disputes in the foundations of mathematics, disputes that struck him as sterile as traditional philosophical debates. In Logische Syntax der Sprache Carnap explicates analyticity in terms of consequence. He exhibits specifications of languages of differing logical strengths all of whose mathematical truths are analytic. Carnap thus seeks to persuade us that mathematics flows from the defining rules of a language. He maintains that foundational debates arise from the adoption of different languages. Tolerance counsels that these quarrels should be replaced by the metamathematical investigation of languages formalizing various foundational approaches. It should be noted, however, that the mathematics required in Carnap's metalanguage for the crucial definition of consequence makes his understanding of the analyticity of mathematics vulnerable to the charge of vicious circularity.

Carnap applies logical syntax to the problem of explicating empirical testability (Carnap, 1936, 1937). For Carnap, empiricism is not a thesis; it is rather a recommendation that investigators restrict themselves to certain languages as the frameworks for formalizing scientific theories. Here again we see Carnap's distinctive approach to philosophy: the explication (that is, the replacement) of a hitherto philosophical notion by a precise, formal notion and the corresponding construal of a philosophical thesis as the recommendation of a linguistic framework.

  • Der logische Aufbau der Welt (Weltkreis-Verlag Berlin. 1928); trans. R. George, The Logical Structure of the World (Berkeley: University of California Press. 1969).
  • Foundations of Logic and Mathematics, in Foundations of the Unity of Science, vol. 1, ed. Neurath, O. et al. (University of Chicago Press Chicago. 1939), 139-213.
  • Logische Syntax der Sprache (J. Springer Vienna, 1934); trans. Smeaton, A. , The Logical Syntax of Language (Routledge and Kegan Paul London, 1937).
  • Meaning and Necessity (University of Chicago Press Chicago, 1947).
  • “Testability and Meaning,” Philosophy of Science 3 (1936), 419-71; Philosophy of Science 4 (1937), 1-40.
  • Schilpp, P.: The Philosophy of Rudolf Carnap (Open Court La Salle, IL, 1963).
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