Abstract
This paper includes an unpublished interview with Rudolf Carnap, conducted originally in 1961 by the sociologist Warren Hagstrom. It concerns Carnap’s views on metaphilosophy, disagreement in philosophy, his role in the foundational debate, and his views on the relation of philosophy to logic and mathematics. The interview is supplemented with an editorial introduction, contextualizing the discussion.
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- 1.
This view of Carnap about freedom, responsibility, and emphasizing the inner capability of making matured decisions about one’s life and values goes back to Carnap’s youth when he was a member of the so-called German Youth Movement. This idea is explored in great detail by Carus (2007) and in the chapters of Damböck et al. (2021).
- 2.
There is another interesting line of thought in the interview, namely a finitist motive. While the logical space of reasons and possible paths might be infinite, our life and practical possibilities are finite, thus we have to make decisions. As Carnap says in the interview: “Here we are concerned with the fact that every philosopher and every scientist has to make up his mind which way to take because there is not enough time to try to all possible ways, and therefore he chooses his approach according to his mostly unconscious judgment or feeling or hunch of fruitfulness of this or that approach.” This might even come close to the idea that Carnap often expressed (e.g. in the preface to the Aufbau), namely that philosophy is a collective enterprise; thus as a collective, philosophers might explore different paths, which might lead to different results, but as they contribute to the same enterprise, they do not fight or compete with each other but supplement each other’s inquiries.
- 3.
One of the main examples of disagreement in the interview concerns debate over the foundations of mathematics; the other major example concerns, however, what is usually called the debate between ideal and ordinary language philosophy. By the time the interview was conducted Carnap already read and replied to all of the paper in his forthcoming Festschrift, The Philosophy of Rudolf Carnap, which included numerous pieces that concerned the philosophy of language. But one of them was especially relevant in this context, namely Peter Strawson’s “Carnap’s View on Constructed Systems versus Natural Languages in Analytic Philosophy” (Strawson 1963). In his reply, Carnap emphasized his method of explication and its relevance to ordinary language and claimed that “language, whether natural or artificial, is an instrument that may be replaced or modified according to our needs, like any other instrument” (Carnap 1963b, 938). Regarding this debate (see, e.g., Franco 2018), this interview contains some nuances and further considerations as well; even about how Carnap viewed the history and ramification of analytic philosophy (or philosophies).
- 4.
See Hagstrom to Carnap, March 5, 1961 (ASP RC 089–50-03), Hagstrom to Carnap June 24, 1961 (ASP RC 089–50-02), and Carnap to Hagstrom September 23, 1961 (ASP RC 089–50-01). Nonetheless, Carnap’s name does not appear in Hagstrom’s book. See Hagstrom (1964). Nonetheless, Carnap’s interview is often quoted by Hagstrom, referring to him as “an eminent logician”.
- 5.
- 6.
Note, however, that Carnap accepted a broader picture of philosophy of science as well, a so-called bipartite metatheory in which both the sociological and the logical inquiries have their own important place, contributing to the general enlightening program. See Uebel (2012).
- 7.
- 8.
“Not” is put into parentheses and underlined by pencil, seemingly by Carnap.
- 9.
Augustus De Morgan (1806–1871) was a British mathematician and logician; “De Morgan’s laws” are named after him. The laws concern the expression of conjunction and disjunction in terms of each other with negation.
- 10.
Carnap has in mind Frege’s Grundgesetze der Arithmetik (Jena: Verlag Hermann Pohle, Band I/II), translated recently completely by P. Ebert and M. Rossberg (with C. Wright) as Basic Laws of Arithmetic: Derived using concept-script, Oxford: Oxford University Press, 2013.
- 11.
About the detailed reception of Frege’s work, and how his reception influenced him, see Dale Jacquette, Frege: A Philosophical Biography, Cambridge: Cambridge University Press, 2019.
- 12.
Leopold Kronecker (1823–1891) was a German mathematician who criticized heavily Cantor’s set theory. The mentioned saying of Kronecker comes presumably from a 1886 lecture of his.
- 13.
Carnap has spent the winter semester 1910/11, the summer semester 1913 and the summer semester 1914 with Frege in Jena. His lecture notes of the courses “Begriffschrift I, II” and “Login in Mathematics”, have been published in Frege’s Lectures on Logic: Carnap’s Student Notes 1910–1914, trans. and ed. by Erich H. Reck and Steve Awodey. Chicago and LaSalle, Illinois: Open Court, 2004.
- 14.
Although Russell has read some of Frege’s work already in 1895, he did not understand it that time due to Frege’s special symbolism. He famously notified Frege, however, that he has found a contradiction in his system in 1902, already after he [Russell] was working on his own system.
- 15.
In fact, though most of them were dismissive, critical and deeply misunderstood his endeavor, Frege’s first book, the Begriffschrift earned at least six reviews by such figures as Reinhold Hoppe, Kurd Lasswitz, Paul Tannery, Karl Michaëlis, Ernst Schröder, and John Venn.
- 16.
The Association for Symbolic Logic was founded in late 1935 (after a year of discussions at Harvard); its first president was C.J. Ducasse and vice-president H.B. Curry. On its early history see C.J. Ducasse and H.B. Curry, “Early history of the Association for Symbolic Logic,” The Journal of Symbolic Logic 27 (3) (Sep. 1962): 255–258.
- 17.
Carnap has spent the academic year 1940/41 at Harvard. See Greg Frost-Arnold, Carnap, Tarski, and Quine at Harvard: Conversations on Logic, Mathematics, and Science, Chicago: Open Court, 2013.
- 18.
Carnap arrived to the States in December 1935 for the tercentennial of Harvard, celebrated in late 1936, where he was an invited speaker and took his honorary doctoral degree.
- 19.
Edwin Boring (1886–1968) was an American experimental psychologist at Harvard. He wrote a lot about the history of psychology, e.g. A history of Experimental Psychology (New York: Century, 1929), and Sensation and Perception in the History of Experimental Psychology (New York: Appleton-Century-Crofts, 1942).
- 20.
The University of California, Berkeley has initiated in 1957 an interdisciplinary graduate program about logic and methodology of science, following the ideas of Alfred Tarski. The program still exists today; about its history, see Paolo Mancosu, “The Origin of the Group in Logic and the Methodology of Science,” Journal of Humanistic Mathematics 8 (1) (January 2018): 371–413.
- 21.
Percy W. Bridgman (1882–1961) was a Nobel Prize winner American physicist; among philosophers he is mainly known for his work on philosophy of science, especially on operationalism. About the early history of Bridgman and the Vienna Circle, see Sander Verhaegh, “The American Reception of Logical Positivism: First Encounters, 1929–1932,” HOPOS: The Journal of the International Society for the History of Philosophy of Science 10 (1) (Spring 2020): 106–142.
- 22.
See, e.g., Carnap, “Inductive Logic and Inductive Intuition,” in Imre Lakatos (ed.), The Problem of Inductive Logic, Amsterdam: North Holland, 1968, pp. 258–314.
- 23.
John von Neumann (1903–1957) was a Hungarian mathematician, physicist, and computer scientist.
- 24.
Hermann Weyl (1885–1955) was a German mathematician, physicists and philosopher. He worked quite early on the theory of relativity; in his philosophy of physics, Weyl followed the path of Edmund Husserl’s phenomenology and Brouwer’s intuitionism at the same time until the late 1920s.
- 25.
Alfred Tarski (1901–1983) was a Polish logician and mathematician who emigrated to the United States in 1939. Previously he was a leading member of the prominent Lwów-Warsaw School of logic and mathematics; in the US, he thought logic and mathematics at the University of California, Berkeley from 1942 till his death in 1983.
- 26.
Chen Chung Chang (1927–2014) was a Chinese logician who obtained his PhD from Berkeley in 1955 under Tarski’s supervision. Later he became a professor of mathematics at UCLA.
- 27.
Richard Montague (1930–1971) was an American mathematician, philosopher, and linguist.
- 28.
Chang, Montague and Tarski initiated a bi-weekly Logic Colloquium in the late 1950s, and organized it through the 1960s.
- 29.
Georg Cantor (1845–1918) was a German mathematician, known mainly for his early works on set theory.
- 30.
Carnap talks about “The Second Conference on the Epistemology of the Exact Sciences in Königsberg” that took place on September 5–7, 1930. For some details see Friedrich Stadler, The Vienna Circle: Studies in the Origins, Development, and Influence of Logical Empiricism, Dordrecht: Springer, 2015, 161–166.
- 31.
Arend Heyting (1898–1980) was a Dutch mathematician and logician, mainly known for his work intuitionism.
- 32.
L.E.J. Brouwer (1881–1966) was a Dutch mathematician, logician, and philosophers, mainly known as the founder of intuitionism.
- 33.
Papers of the symposium were published later in Paul Benacerraf and Hilary Putnam (ed.), Philosophy of Mathematics: Selected Readings, Second Edition, Cambridge: Cambridge University Press, 1983 (originally 1964), pp. 41–65.
- 34.
Brouwer was invited to Vienna by the physicist Felix Ehrenhaft in 1928. Some members of the Vienna Circle attended his lectures; famously, Ludwig Wittgenstein was there as well, and many people note this event as his return to philosophy.
- 35.
See, e.g., Heyting, “Die formalen Regeln der intuitionistischen Logik” (1930) and “Die formalen Regeln der intuitionistischen Mathematik I, II” (1931), both published by the Deutsche Akadmie der Wissenschaften zu Berlin. In his Logical Syntax of Language (published originally in German in 1934, translation in 1937, Kegan Paul, Trench, Trubner & Co Ltd.), Carnap noted already that Heyting’s work gave a much better approximation of what intuitionism might be consisted in, and thus made a solid ground for further discussions (see §16, “On Intuitionism”).
- 36.
Carnap left Vienna before the winter semester of 1931 to take his new position in Prague.
- 37.
In the original transcript, “alive” is underlined and marked with a question mark.
- 38.
In the original transcript, “reveal” is underlined and a pencil note says “contain?”.
- 39.
Carnap crossed out this word and wrote another with a question mark with pencil, but it is unreadable.
- 40.
It is unknown to exactly what Carnap refers here. In the literature, the Hilbert-Brouwer controversy is a well-discussed issue, concerning, on the one hand, the foundational debate regarding mathematics, and on the other hand, Hilbert’s act of removing Brouwer from the editorial board of “Mathematische Annalen”. See, e.g., Per Martin-Löf, “The Hilbert-Brouwer controversy resolved?”, in Mark van Atten et al. (eds.), One Hundred Years of Intuitionism (1907–2007): The Cerisy Conference, Basel/Boston/Berlin: Birkhäuser, 243–256. See also J. Posy Carl, “Brouwer versus Hilbert: 1907–1928”, Science in Context 11 (2) (Summer 1998): 291–325.
- 41.
One of the most important documents and official initiators of the debate is Peter Strawson’s paper in the Carnap volume of The Living Philosophers series, see “Carnap’s Views on Constructed Systems versus Natural Languages in Analytic Philosophy,” in P.A. Schilpp (ed.), The Philosophy of Rudolf Carnap, La Salle, Illinois: Open Court, 1963, 503–518.
- 42.
The original transcript has “end of side one”, and the second half of the sentence is missing.
- 43.
William Herbert Sheldon (1898–1977) was an American psychologist and worked on so-called “somatotype psychology:” he tried to find correlations between body types, behavior and social settings.
- 44.
In the original transcript, “today on so-and-so” is underlined by Carnap and marked with a question mark.
- 45.
Paul Bernays (1888–1977) was a Swiss mathematician, known for his work on set theory and the philosophy of mathematics.
- 46.
David Hilbert and Paul Bernays, Grundlagen der Mathematik II, New York/Berlin: Springer, 1939. The first volume, with the same title, also at Springer, was published in 1934.
- 47.
“Not” is underlined with pencil in the transcript, and a question mark is put by pencil on the margin by Carnap.
- 48.
Wilhelm Ackermann (1896–1962) was a German mathematician who obtined his PhD under Hilbert in Göttingen in 1925. Ackermann is known for his work on first-order logic and for his joint textbook with Hilbert that was published in 1928 (Grundzüge der theoretischen Logik, Springer).
- 49.
Gerhard Gentzen (1909–1945) was a German mathematician and logician, known for his wok on natural deductions.
- 50.
Carnap’s views on finitism, with the historical context in mind, is discussed in detail by Greg Frost-Arnold, Carnap, Tarski, and Quine at Harvard: Conversations on Logic, Mathematics, and Science, Chicago: Open Court, 2013.
- 51.
Richard von Mises (1883–1953) was an Austrian mathematician, known for his work on probability, statistics and aeronautics. Von Mises was involved both in the Vienna Circle around Moritz Schlick and in the Berlin Circle around Hans Reichenbach. He emigrated to the United States (after a six year detour to Turkey) in 1939 and taught there at Harvard until his death.
- 52.
John Maynard Keynes (1883–1946) was a British economist who published his famous and influential A Treatise on Probability in 1921.
- 53.
Sir Harold Jeffreys (1891–1989) was an English mathematician and geophysicist. He published his book, Theory of Probability in 1939, and thus initiated the revival of the Bayesian view of probability.
- 54.
Bruno de Finetti (1906–1985) was an Italian statistician and actuary.
- 55.
Leonard J. Savage (1917–1971) was an American mathematician; his well-known book, The Foundations of Statistics was published in 1954.
- 56.
Carnap’s final views on probability are to be found in “A Basic System of Inductive Logic, Part 1”, in Studies in Inductive Logic and Probability, volume 1, edited with Richard C. Jeffrey (Berkeley: University of California Press, 1971), and in “A Basic System of Inductive Logic, Part 2”, in Richard Jeffrey (ed.), Studies in Inductive Logic and Probability, volume 2, Berkeley: University of California Press, 1980, 17–155.
- 57.
This is marked by Carnap with question marks.
- 58.
John G. Kemeny (1926–1992) was a Hungarian-born American mathematician and computer scientist. He exchanged many ideas with Carnap on semantics and model theory in the 1950s.
- 59.
Richard Jeffrey (1926–2002) was an American philosopher and logician, known for his work on probability theory. He worked with Carnap on probability from the late 1950s until the death of Carnap in 1970.
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Acknowledgments
The interview is contained in the Carnap Archive at Pittsburgh: Rudolf Carnap Papers, 1905–1970, ASP.1974.01, Special Collections Department, Archives of Scientific Philosophy, Hillman Library University of Pittsburgh. All rights reserved; I take the chance here to express my gratitude for their permission to publish the interview here.
I was supported by the MTA Lendulet Morals and Science Research Group and by the MTA Premium Postdoctoral Scholarship.
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Tuboly, A.T. (2022). Tolerance, Disagreement, and the Practical Dimension of Philosophy: Warren Hagstrom’s Interview with Carnap. In: Ramharter, E. (eds) The Vienna Circle and Religion. Vienna Circle Institute Yearbook, vol 25. Springer, Cham. https://doi.org/10.1007/978-3-030-76151-6_12
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