Hempel’s Dilemma: Not Only for Physicalism*

ABSTRACT

According to the so-called Hempel’s Dilemma, the thesis of physicalism is either false or empty. Our intention in this paper is not to propose a solution to the Dilemma, but rather to argue as follows: to the extent that Hempel’s Dilemma applies to physicalism it equally applies to any theory that gives a deep-structure and changeable account of our experience or of high-level theories. In particular, we will show that it also applies to mind–body dualistic theories. The scope of Hempel’s Dilemma turns out to be very wide: it is a special case of a general sceptical argument against changeable deep-structure theories in and outside science.

KEYWORDS:

• Hempel’s Dilemma
• deep structure
• dualism
• physicalism
• reduction
• theory change

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Notes

1 Stoljar (2017), in his overview of this question, distinguishes between the ‘theory-based conception’, according to which to be physical is to be something that physical theory tells us about, and the ‘object-based conception’, according to which to be physical is to be something required by a complete account of the intrinsic nature of paradigmatic physical objects and their constituents. We address the former conception.

2 Earlier, in his (1969) paper, Hempel already remarked that (what he calls there) the ‘mechanistic’ thesis is obscure—and it seems to us that he would agree to our ‘extended’ Hempelian Dilemma presented in the next section. Hempel writes: ‘Thus, we face a dilemma. If for the sake of conceptual clarity, we give the thesis of mechanism a linguistic turn, we fail to express its philosophical intent; and if we try to formulate that intent in ontological terms, or in the “material mode,” the resulting statement proves to be seriously obscure and elusive. The same difficulty besets all reductionist theses that are conceived as ontological claims’ (Hempel 1969, 183).

3 Much earlier Feigl (1969) discusses the problem described in the second horn of Hempel’s Dilemma, and says that others are aware of it as well. He writes: ‘Schlick, Carnap, and Reichenbach, who espoused this thesis [of physicalism or the unity of science], were fully aware of its conjectural and hence precarious character. Essentially it endorses a certain program for the current and future development of science towards a unitary or monistic set of explanatory premises. … As a distant goal of this program of unitary explanation, some future theoretical physics is fancied. … This thesis is, of course, not only problematic, but also inevitably vague in that such a theoretical physics may have to be very different from its current stage. All that can be said at the moment is that the ‘style’ of explanation might be somewhat similar to that used in the present stage of the theories of relativity, quantum mechanics, and quantum electrodynamics’ (Feigl 1969, 21).

4 See for example Dowell (2006a), Pineda (2006), Ney (2008a), Stoljar (2010, Ch. 5), Bokulich (2011) and Prelević (2018).

5 Chomsky (1968, 2000, 2003) also argues that all the theories of physics from Newotonian mechanics onwards are meaningless in the sense that they carry no meaning for us, human beings. These theories are, in Chomsky's view, formalisms accompanied by instructions for application in empirical predictions. In his view, all these theories make claims that are incomprehensible by human beings; they exceed our cognitive capacities. The cognitive capacities of human beings are limited by our biological making, and the nature of the material world (as well as the nature of the mental realm) is beyond our grasp. He argues that the last theory that was comprehensible to us was Descartes’s; but it makes false predictions.Dennett, in an interview, responded that while it is by and large non controversial that we are limited qua biological creatures, Chomsky provides no basis for claiming that our limitations lie in understanding physics.

6 van Fraassen (2002) applies this in characterising empiricism.

7 We talk about lower-level theories rather than fundamental theories, avoiding the need to commit to fundamentalism. See Morganti (2020).

8 There are anticipations of the distinction between principle vs. constructive theories in the nineteenth-century and early twentieth-century literature; see e.g. Bechler (1993, Ch. 3.7.10; Howard and Giovanelli 2019). Bechler (1993) argues that Einstein’s idea of a principle theory is essentially connected to Poincare's conventionalism. But we set these issues aside here.

9 For another application of Einstein distinction, see Shenker (2015); Hemmo and Shenker’s (2021) analyses of Davidson’s (1970) anomalous monism in its terms; and compare between the structures of the arguments by Einstein (1905a) and Davidson (1970).

10 Hence we need not be committed here to there being a most-fundamental level, that is, to fundamentalism in this respect.

11 Here are some examples of such problems. One problem in contemporary physics includes the well-known incompatibility between quantum mechanics and general relativity. There are ongoing attempts to build a ‘deeper structure’ theory (a notion we discuss below) from which the main facts described by quantum mechanics and general relativity will emerge, but those are still work in progress and give rise to debates concerning their merits and even acceptability. Another problem in contemporary physics is the measurement problem in quantum mechanics: here some people think that the problem has been solved, but this point is under debate. A third problem is the account of the direction of time (if there is any) and—even more severely—the flow of time and the notion of the present. A fourth problem concerns the need to employ mathematical ideas in physics that some people think are dubious. There are other examples, and the reader may provide more, from physics as well as from other sciences.

12 Anti-de Sitter (AdS) space is the maximally-symmetric spacetime of constant negative curvature. Our universe (according to the best estimates) has a small positive cosmological constant. Nevertheless, the AdS space presents many of the puzzles associated with quantum gravity.

13 Also: it seems to us that the stance approach shares the merits and demerits of non-cognitivist approaches in meta-ethics (see van Roojen 2018), but we do not address this issue here.

14 An anonymous reviewer, in suggesting that we are able to know what mental is without relying on some theory, compared this to knowledge of what a square is, which is allegedly possible in a way that does not depend on a theory of squareness. People use the word ‘square’ in daily contexts, sometimes correctly and sometimes incorrectly. How can we say which is which? Do we not rely on theory? Famously, rich contents were added to the notions of Euclidean geometry when Hilbert offered his 20 axioms of Euclidean geometry.

15 The case of ghosts that Montero (1999) brings in invites a different sort of consideration, since here: (i) With regard to the mental vs. physical distinction, although it seems clear that ghosts are nonmental, it is harder to say whether or in what sense they are physical; (ii) Another issue concerns existence (e.g., of ghosts): one needs to consider what are the criteria for existence and whether there are different sorts of existence in the first place and what are they.

16 For an argument that physics is fundamental, see (Morganti 2020).

17 Although this is not our main subject here, let us make two very brief comments about the brute facts option. (1) We doubt that in any particular example the brute facts idea is taken seriously: we doubt whether anyone seriously thinks that the fact that my pain is not realised by, say, my cup of coffee, is a mere brute fact. (2) We vehemently object to the idea that brute facts accounts are even legitimately acceptable in science and philosophy, since we see them as forms of mysterianism, that merely prohibit the search for explanation and are therefore detrimental to progress.

18 This statement is false to a large extent according to contemporary science; we have learned a lot about the physiology of pain since Kripke came up with this example in the 1970s. However this falsity doesn’t matter for our present argument (especially in the context of discussing Hempel’s Dilemma), and therefore we choose to stick with this famous example.

19 Here we assume that all names in the above sentences are what Kripke (1980) calls ‘rigid designators’.

20 We consider (c) below: it is easier to make our point without the difficulties surrounding mental terms.

21 Or otherwise, given any appropriate understanding of the notion of cause, including a deflationary notion. See Ben-Menahem (2018) on causation in physics.

Additional information

Funding

This work was supported by Israel Science Foundation [grant number 1148/18], [grant number 690/21].