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Carnapian rationality


It is generally thought that Carnap’s principle of tolerance cannot be integrated into a coherent overall conception of rationality. The doubts come from many sides, of which two are singled out. This paper argues (and documents) that both are wrong, and that Carnapian rationality is a viable and perhaps quite interesting program for further development.

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  1. Quoted by Stein (1998, p. 3). The general perspective developed in this paper owes a great deal to Stein’s writings—not only to those cited—as well as his personal influence as a teacher.

  2. E.g. in his later paper “The Aim of Inductive Logic” (Carnap 1962).

  3. This passage, originally in Sect. 12 of Carnap’s (1963) autobiography, was omitted from the published version.

  4. Of course one might accept Carnapian accounts of both “analytic” and “a priori” and still reject Carnap’s argument here, e.g. because one rejects his conception of probability. This is bracketed here; Carnap’s conception of probability and induction is used in this paper only to illuminate his larger conception of rationality, and nothing depends on it.

  5. As Carnap puts it in the unpublished typescript discussed further down in this paragraph (ASP/RC 082-07-01, p. 10).

  6. Where the emphasis is on “first-hand”—the relevant intuitions are those of active users, not passive commentators or consumers. Carnap suggests this in his reply to Ernest Nagel when he says that Nagel’s intuitions would change if he actually tried to construct a logic of confirmation himself: “\(\ldots \) since the time I began to construct a system of inductive logic, I myself had sometimes to change intuitive judgments on certain properties of logical probability. And this occurs still today when I begin to think about the extension of inductive logic to a new, more complex language form. If Nagel were to try to construct a system of [degree of confirmation] on the basis of his present intuitive judgments, I am convinced that he would change quite a number of these judgments because he would find that the system would yield many results which would appear to him either as undesirable or even as entirely unacceptable. From experiences with my own intuitive judgments and those of friends whom I often asked for reactions to particular results, I have learned that isolated intuitive judgments are often very unreliable. Of course, the development of inductive logic must be guided by intuitive inductive judgments. But these judgements are more useful if they are made, not on isolated points, but in the context of the tentative construction of a system.” (Carnap 1963, p. 994)

  7. Any more than he was the least fazed by Arne Naess’s research showing that half the population did not use the truth predicate in accordance with Tarski.

  8. Though Carnap may well have written the section on uniformity of nature (§41F, quoted above, Sect. 1) in 1949, as he says in the original draft of his autobiography, the discussions with Feigl go back to at least April 1942, i.e. before he wrote the rest of the book; a diary entry says “Mit Feigl ausführlich über dc [degree of confirmation]. (Er: darin steckt immer faktische Annahme über Gleichförmigkeit der Natur.)” (ASP/RC 025-82-08, 26 Apr 1942) Carnap also made several notes on uniformity of nature at around this time, mentioning Feigl’s question about what factual assumptions underlie Carnap’s proposed degree of confirmation (ASP/RC, folder 078-25). So the fact that Carnap wrote section 41F later likely meant that he was not yet satisfied he had worked out this problem to his own satisfaction by 1944–1946.

  9. Feigl presumably has in mind Burks (1953) and Feigl (1954).

  10. Hempel makes specific reference to the passage from §18 of Continuum of Inductive Methods quoted above, and asks whether “while the choice of a c-function, to be sure, need not rest on any empirical assumption, the problem remains whether the justification of such a choice as adequate would require reference to empirical fact\(\ldots \) I wonder whether you could not add a word about that question, because otherwise the reader might feel that your reply sidesteps a crucial issue at stake.” (ASP/RC 089-57-03, p. 2)

  11. Since Carnap is an emotivist, according to one such critic, “value statements lack cognitive content; they do not have any truth-value. But then the justification of science on the basis of ethics is not really a justification at all since the claim about the good life merely expresses Carnap’s emotive state or disposition toward life.” So “emotivism in ethics severed the crucial link between science and the good life as he envisioned it. Perhaps this is the ultimate aporia of logical empiricism.” (Irzik 2003, pp. 343–344)

  12. This widespread view projects a Wittgensteinian absolutism regarding the “boundaries” of language onto Carnap, who explicitly rejected it and endorsed a gradualist conception, e.g. in Carnap (1963, p. 934).

  13. One of the clearest statements of the tradeoffs between such a position, attributed to Carnap, and a Quinean position where we are simply inside whatever framework we are in, in mediis rebus (Dreben 1994), without access to its basic framework principles, let alone the ability to choose them, is that of George (2012), concluding: “But for Carnap, as we have seen, such considerations can at best exert a non-rational influence on an agent who is choosing which framework to adopt. Talk of rational constraint only has its place within a framework, once a language and rules of reasoning and inquiry have been settled upon. For Carnap, this observation is critical in understanding why traditional philosophical disputes have proven to be so frustratingly irresolvable and so different from scientific disagreements: philosophers, unlike scientists, typically dispute about which framework to adopt, which language to speak, and no facts about the world can rationally bear on such disagreements. The empirical facts only come into focus, and talk of rational relevance only gets a grip, once a particular linguistic framework has been adopted.” (George 2012, p. 10)

  14. Cf. the discussion of Stein’s conception of pragmatics more generally in Carus (2010).

  15. Which is again not to claim that the non-traditional, non-conformist origins of knowledge or values make them inherently “better,” certainly not by any absolute standard, though presumably there is a better chance for knowledge generated within the constraints of a given value system to be “better” by the standards of that value system.

  16. Among the better-known milestones in this tradition of Enlightenment critique are the Romantic (and Goethean) rebellion against the portrayal of nature in terms of “Zahlen und Figuren,” Adorno’s and Horkheimer’s “dialectic of enlightenment,” and Richard Rorty’s rejection of science as a cognitive exemplar (Carus 2007, Ch. 1).

  17. These examples suggest that he would have liked the general approach, at least, of Nozick’s list of 23—progressively stronger—conditions for constraining “rational” utility functions in the section “Rational Preferences” of a chapter entitled “Instrumental Rationality and its Limits” (Nozick 1993, pp. 139–151). Nozick does not argue explicitly that there is no genuine distinction between instrumental and substantive rationality, but by the end of this list it is hard to deny that the boundary is much less clear-cut than the rhetoric surrounding this debate usually suggests.

  18. Wood (2006) portrays Kant as rejecting the idea that there could be fundamentally different “supreme principles of morality,” and as arguing that practical reason shows all such supreme principles to be equivalent. This would make Carnap’s loose and pluralistic practical reason even more un-Kantian than suggested above.

  19. In precisely this context of a threatening regress of languages in which to specify quantifiers of object

    languages lower in the hierarchy: “\(\ldots \) in practice, we end the regress of background languages, in discussions of reference, by acquiescing in our mother tongue and taking its words at face value.” (Quine 1969, p. 9)

  20. Ricketts (2004) disagrees, citing Carnap’s reply to Evert Beth: “Since the metalanguage ML serves as a means of communication between author and reader or among the participants in a discussion, I always presupposed, both in syntax and in semantics, that a fixed interpretation of ML, which is shared by all participants, is given.” (Carnap 1963, p. 929) But Carnap himself, in the same text, makes explicit that he does not intend this shared default language to be taken at face value. “It seems to be obvious that , if two men wish to find out whether or not their views on certain objects agree, they must first of all use a common language to make sure that they are talking about the same objects\(\ldots \) It is of course not quite possible to use the ordinary language with a perfectly fixed interpretation, because of the inevitable vagueness and ambiguity of ordinary words. Nevertheless it is possible at least to approximate a fixed interpretation to a certain extent, e.g. by a suitable choice of less vague words and suitable paraphrases.” (ibid., pp. 929–930)

  21. Though a very different one from that held out by the ordinary language philosophers, who considered ordinary language the philosopher’s “sole and essential point of contact with reality” (Strawson 1963, p. 518). For Quine, the status of ordinary language is much more problematic, since it has no independent authority (the parts of it found defective, within the conceptual scheme as a whole—in the light of regimentation—are to be eliminated), but is nonetheless a kind of default standpoint.

  22. Here again, as in the case of Stein’s extrapolation from Carnap above, some interpretive leeway is required that some readers may find too wide, and reject as incompatible with their conception of Carnap’s overall perspective. In this case, the leeway in question is that suggested by Thomas Uebel (2007, p. xvi) regarding what he sees as the “emerging consensus on metaphilosophical matters on the so-called left wing of the Vienna Circle,” which includes not only Carnap and Neurath but also Philipp Frank and Hans Hahn, among others; see also Uebel (2004), and further discussion on the “scientific vernacular” in Carus (2007, Ch. 11).

  23. Frankfurt (1971) introduced this idea into the moral philosophy literature, where it has been current ever since, but never high profile, any more than in economics, despite the occasional efforts of Amartya Sen.

  24. For instance, in Carnap (1962, p. 312): “In the sphere of human action we have first concepts describing overt behavior, say of a boy who is offered the choice of an apple or an ice cream cone and takes the latter; then we introduce the concept of an underlying momentary inclination, in this case the momentary preference of ice cream over apple; and finally we form the abstract concept of an underlying permanent disposition, in our example the general utility function of the boy\(\ldots \) When we wish to judge the morality of a person, we do not simply look at some of his acts, we study rather his character, the system of his moral values, which is part of his utility function. Single acts without knowledge of motives give little basis for a judgment\(\ldots \)

  25. On the distinction between “framework” and “content” values as characteristic of the liberal, Anglophone wing of the Enlightenment tradition (in contrast to the continental, engineering-oriented wing), see Carus (2007, pp. 296–7ff.).

  26. “Roughly” since not everyone accepts every current theory (or alleged fact) in every scientific and historical discipline. But there will be an “overlapping consensus” among all those who use the scientific vernacular, and the ultimate source of this overlap—empirical evidence—is a more compelling motivation than the supposed “reasonableness” of the contending “comprehensive doctrines” that drives Rawls’s well-known version of such an overlapping consensus (Rawls 1996, pp. 58–66). Of course it could perhaps be argued that all Rawls means by “reasonableness” here is, in fact, a willingness to accept and use the scientific vernacular.

  27. A comparison of Kuhn and Stein in this respect, with particular emphasis on Stein’s Carnapian pragmatics, is to be found in Carus (2013).

  28. This is the upshot of the “reciprocal containment” discussed by Ricketts (2009); on Quine’s “universalism” cf. Hintikka (1990) and Quine’s (1990) thin-skinned but hardly convincing response.

  29. Friedman’s (2001, pp. 47–68, 105–115; 2011, pp. 712–729) argument to the effect that object-level Kuhnian incommensurability (e.g. during scientific revolutions) can coexist with meta-level rationality at the level of philosophical or meta-scientific debate (e.g. the debate about geometry between Poincaré and Helmholtz as a backdrop to Einstein’s introduction of relativity) makes essentially this same point; Carnap would have classified such meta-scientific debate as belonging to descriptive pragmatics.

  30. See Shimony (1977) for a balanced discussion, which however appears somewhat to misconstrue the aims of Carnap’s critique.

  31. Which would invite the kind of circularity charge sometimes levelled at Quine, discussed in depth by Gregory (2008); cf. also the review of Gregory’s book by Burgess (2009).

  32. Michael Friedman provides good examples of this in his cases of philosophical, meta-scientific debate guiding object-level scientific change (footnote 29 above).


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The unpublished texts listed above are quoted by permission of the University of Pittsburgh and the Carnap heirs, respectively, which is gratefully acknowledged. I am also grateful to Georg Schiemer for organizing the conference at the Munich Center for Mathematical Philosophy in July 2013 where an earlier version of this paper was presented, as well as to Thomas Uebel, Florian Steinberger, Pierre Wagner and two anonymous referees for perceptive comments that greatly improved the paper. The influence of many conversations with Howard Stein and Michael Friedman on the overall viewpoint of the paper is pervasive.

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Carus, A.W. Carnapian rationality. Synthese 194, 163–184 (2017).

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