In This Article Rudolf Carnap

  • Introduction
  • Surveys and Orientation
  • Carnap’s Works
  • Carnap’s Beginnings
  • The Aufbau
  • Critiques of the Aufbau, and Its Later Influence
  • Reconstructions and Technical Critiques of the Aufbau
  • The Vienna Circle
  • From the Aufbau to the Syntax
  • The “Protocol-Sentence Debate” and Physicalism
  • Carnap, Wittgenstein, Heidegger
  • Logical Syntax of Language
  • Misunderstandings and Critiques of Logical Syntax
  • Logicism and Philosophy of Mathematics
  • Semantics
  • Critiques and Misunderstandings of Carnap’s Semantics
  • “Testability and Meaning” and Criteria of Empirical Significance
  • Modal Logic
  • Probability and Induction
  • Carnap vs. Quine
  • Carnap vs. Quine on Analyticity
  • Later Debates on Analyticity
  • Carnap vs. Quine on Ontology
  • “Empiricism, Semantics, and Ontology”
  • Theoretical Concepts
  • Carnap and Gödel—Again
  • Unity of Science, the Encyclopedia, and Kuhn
  • Values
  • Carnap’s Voluntarist Conception of Philosophy
  • Explication

Philosophy Rudolf Carnap
A.W. Carus
  • LAST REVIEWED: 08 October 2015
  • LAST MODIFIED: 10 March 2015
  • DOI: 10.1093/obo/9780195396577-0248


Rudolf Carnap (b. 1891–d. 1970) was acknowledged as the principal philosophical spokesman for the movement known as “logical empiricism” or “logical positivism,” and the leading philosopher of the “Vienna Circle” of the late 1920s and early 1930s. He first became widely known for his 1928 book Der logische Aufbau der Welt (The Logical Construction of the World), which was generally seen as attempting to carry out a positivistic or phenomenalist reduction of all knowledge to sense data—an impression that has only recently been corrected. Carnap’s attention then shifted to the philosophy of logic and mathematics. His next major book, the 1934 Logical Syntax of Language, sought to resolve the debate among the foundational schools of logicism, intuitionism, and formalism (then at its height) by proposing a “principle of tolerance,” according to which there is no ultimately “correct” logic, but only more and less useful ones for various human purposes. This became the guiding principle for his entire later philosophy, including his program of “explication” or piecemeal replacement of vague ideas and concepts by better ones. After Carnap’s emigration to the United States in 1936, the larger ethical and political context of his work—obvious in Central Europe to followers of the Vienna Circle and surrounding debates—went unrecognized, and his experimentation with new language forms came to seem somewhat recondite and technical, even after his shift in focus during the 1940s to inductive logic and probability. Although his major 1950 book Logical Foundations of Probability reshaped the field and led eventually to current Bayesian epistemology and decision theory, it was viewed as a narrowly technical preoccupation. Moreover, by this time, Carnap’s philosophy had come under widespread attack from younger philosophers, especially Quine, who shaped his generation’s understanding of Carnap, which remained in place until quite recently. By the time of Carnap’s major restatement of his views in The Philosophy of Rudolf Carnap (1963), therefore, philosophers had mostly lost interest, and the wider intellectual world saw Quine and Kuhn as having decisively superseded logical empiricism. This only began to be seriously questioned some two decades after Carnap’s death, when the historical turn in analytical philosophy led to closer investigation of many classical texts. Since about 1990, re-interpretations of Carnap’s works have proliferated, and the literature on various aspects of his philosophy has grown at an increasing rate.

Surveys and Orientation

There is a curious ambivalence to the general character of Carnap’s philosophy. From a certain viewpoint, his work appears to be very much in the mainstream of western philosophy—he can be recognized as working within certain traditions of thought, and his philosophical development can be accounted for, to some degree, as responses to those traditions. But from another angle of view, he stands very much outside the philosophical tradition, with which he never had much patience and to which he made only grudging concessions; most of his published work is stiffly expository and technical, hence less than suitable for orientation. Such overall surveys as exist do quite a good job from the first viewpoint but not the second—reasonably enough, as they mostly come from philosophers. Probably the best place to start is Friedman and Creath 2007. There is no suitable single-authored survey in English, though Friedman 2000 puts the early Carnap in a wide overall context, as do the early chapters of Carus 2007. For those who read German, Mormann 2000 is genuinely introductory in a way none of the other items in this section are, but (perhaps for that reason) it is somewhat limited in scope. An orientation to the revolutionary ramifications of the “principle of tolerance” central to Carnap’s thought can be obtained from Ricketts 1994 or Creath 2009. For those interested in the second, more anti- or aphilosophical aspect of Carnap’s thought, there is no overall orientation, but Uebel 2004 sketches a general context, Bouveresse 2012 gives an interestingly different one, and Carus 2007 (chapters 1–3) provides extensive material. Carnap’s own published autobiography, though significantly cut from the original manuscript (preserved in the Carnap papers at the University of California, Los Angeles), is nonetheless an important introductory document, included in Carnap 1963a (cited under Carnap’s Works).

  • Bouveresse, Jacques. “Rudolf Carnap and the Legacy of Aufklärung.” In Carnap’s Ideal of Explication and Naturalism. Edited by Pierre Wagner, 47–62. New York: Palgrave Macmillan, 2012.

    DOI: 10.1057/9780230379749E-mail Citation »

    Abridged translation of “Rudolf Carnap et l’héritage de l’Aufklärung.” In Jacques Bouveresse’s Essais VI: Les lumières des positivistes, 55–133; Marseille: Agone, 2011. Broad discussion of the predicament of the Enlightenment in 20th-century Europe and Carnap’s place in that interplay of ideas.

  • Carus, A. W. Carnap and Twentieth-Century Thought: Explication as Enlightenment. Cambridge, UK: Cambridge University Press, 2007.

    DOI: 10.1017/CBO9780511487132E-mail Citation »

    Looks for the architectonic unity of Carnap’s thought in his ideal of explication, mostly by way of how Carnap arrived at it—via early influences, his first writings, the Aufbau, up to the Syntax and a bit beyond, against a wide array of archival documents that provide narrative continuity.

  • Creath, Richard. “The Gentle Strength of Tolerance: The Logical Syntax of Language and Carnap’s Philosophical Programme.” In Carnap’s “Logical Syntax of Language.” Edited by Pierre Wagner, 203–216. New York: Palgrave Macmillan, 2009.

    DOI: 10.1057/9780230235397E-mail Citation »

    The principle of tolerance considered more broadly as an argumentative (not merely rhetorical) strategy, illustrating just how radical a move it is, and how unprecedented in the history of thought. Stresses that the program behind tolerance is a positive, creative engineering program more than a negative, anti-metaphysical one.

  • Friedman, Michael. A Parting of the Ways: Carnap, Cassirer, Heidegger. LaSalle, IL: Open Court, 2000.

    E-mail Citation »

    Reconstructs the epoch-making philosophical encounter in Davos between the establishment Neo-Kantian Ernst Cassirer and the upcoming “secret king” of German philosophy, Martin Heidegger. Carnap also attended. The different responses of Carnap and Heidegger to the Neo-Kantian problematic epitomize the ensuing split between analytical and continental traditions in philosophy.

  • Friedman, Michael, and Richard Creath. The Cambridge Companion to Carnap. Cambridge, UK: Cambridge University Press, 2007.

    DOI: 10.1017/CCOL9780521840156E-mail Citation »

    Collection of introductory papers by leading Carnap scholars covering most aspects of Carnap’s work, with a valuable overview introduction by Friedman that also reflects critically on the Carnap literature as a whole, including his own previous work. Several of these papers are cited separately in other sections of this article.

  • Mormann, Thomas. Carnap. Munich: C. H. Beck, 2000.

    E-mail Citation »

    The only brief introduction to Carnap for the nonspecialist. Very readable and literate; places its subject in a broad context. Concludes by presenting Carnap’s philosophy as one of “possibilities” in the spirit of Robert Musil’s “Möglichkeitsmenschen” (people who imagine possibilities envisaging the world as being different from the way it is).

  • Ricketts, Thomas. “Carnap’s Principle of Tolerance, Empiricism, and Conventionalism.” In Reading Putnam. Edited by Peter Clark and Bob Hale, 176–200. Oxford: Blackwell, 1994.

    E-mail Citation »

    One of the best and clearest expositions of the import and the larger philosophical significance of Carnap’s principle of tolerance.

  • Uebel, Thomas. “Carnap, the Left Vienna Circle, and Neopositivist Antimetaphysics.” In Carnap Brought Home: The View from Jena. Edited by Steve Awodey and Carsten Klein, 247–278. LaSalle, IL: Open Court, 2004.

    E-mail Citation »

    Paints a vivid picture of the Vienna Circle in its “political” context, broadly speaking (especially the “left” Vienna Circle, the subgroup to which Carnap belonged), with “bewusste Lebensgestaltung” (conscious shaping of life) at the center of its agenda, and the anti-metaphysical impulse a desire to shake off the conservative burden of the past.

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