Abstract
Conceivability arguments (Descartes in Discourse on method; and, meditations on first philosophy, Hackett Pub. Co, Indianapolis, 1993; Kripke in: Munitz (ed) Identity and Individuation, New York University Press, New York, pp 135–164, 1971; Kripke in Naming and necessity, Harvard University Press, Cambridge 1980; Jackson in Philos Stud 42(2):209–225, 1982; Chalmers in The conscious mind: in search of a fundamental theory, Oxford University Press, Oxford, 1996; Chalmers in: Chalmers (ed), The character of consciousness, Oxford University Press, Oxford, 2010) constitute a serious threat against reductive physicalism. Recently, a number of authors (Bayne in Philosophia 18:265–270, 1988; Marton in Southwest Philos Rev 14(1):131–138, 1998; Sturgeon in Matters of mind: consciousness, reason, and nature, Routledge, Abingdon, 2000; Frankish in Philos Q 57(229):650–666, 2007; Brown in J Conscious Stud 17(3–4):47–69, 2010; Campbell et al. in Philos Q 67(267):223–240, 2017; VandenHombergh in Analysis 77(1):116–125, 2017) have proven and characterized a devastating logical truth, (IN), centered on these arguments: namely, that their soundness entails the inconceivability of reductive physicalism. In this paper, I demonstrate that (IN) is only a logical truth when reductive physicalism is interpreted in its stronger, intrinsic sense (e.g., as an identity theory), as opposed to its weaker—yet considerably more popular—extrinsic sense (e.g., as a supervenience theory). The basic idea generalizes: perhaps surprisingly, stronger (intrinsic) forms of reduction are uniquely resistant to the conceivability arguments opposing them. So far as the modal epistemology of reduction is concerned, therefore, it pays to go intrinsic.
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Notes
In what follows, “physical” will cover both physical and functional properties. For a range of examples from the phenomenal domain, see especially Chalmers (1996).
It is worth mentioning that some philosophers have apparently bitten the bullet, arguing that physicalism is inconceivable (see, e.g., Chalmers 2010). The bite is then softened by an insistence that physicalism may be conceivable in some sense, albeit not in the sense relevant to conceivability-possibility entailment principles relied on in the defense of (IN). While the discussion here is fairly involved, it is difficult to see how this move might avoid controversy. Campbell et al. (2017) persuasively argue that it requires an argument, the existence of which undermines the purpose of any independent conceivability argument. VandenHombergh (2017) mentions that the “prima facie negative conceivability” of physicalism—offered as an olive branch in Chalmers 2010; cf. his 2002—would merely collapse to possibility-entailing senses of conceivability. For that matter, it is hard to see how a dualist might advance both the prima facie conceivability of physicalism and the (required) ideal conceivability of zombies, without reducing this central issue of consciousness metaphysics to mere intuition-mongering. Perhaps it is mere intuition-mongering, but less drastic measures ought first to be considered.
This terminology is unique to Campbell et al. (2017), but the assumption is more or less the same (as I will discuss below).
Rudd and Naegle do not explicitly conclude in favor of reductive physicalism, given various background assumptions. Nevertheless, both arguments are opposed to epiphenomenalism, and, given the abandonment of certain assumptions, could work in favor of the reductive position (cf. Chalmers 1996, ch. 5).
This symmetry is reflected in the details of the corresponding formalism: to capture the semantic rigidity of terms in a first-order modal language, one must endorse the conjunctive axiom schema ((s = t ⊃ □(s = t)) ∧ (s ≠ t ⊃ □(s ≠ t))) (cf. Garson 2013).
Note: we might have equally let the actual world instantiate no properties at all, and the model still would have succeeded. Nevertheless, I included the (slightly more complex) model in order to show that the invalidity of (INEP) is consistent with what all (non-eliminative and non-idealist) parties to the dispute accept: there are at least some physical and phenomenal properties which actually instantiate.
In his words, MT is defined as the thesis that “All facts of (phenomenal) consciousness logically supervene on the totality of fundamental (micro-) physical facts” (Marton 1998). MT is equivalent to extrinsic physicalism, so long as: “facts” are understood as “property instances,” “logical supervenience” is understood as “metaphysical supervenience” (itself understood as metaphysical necessitation), and “the totality of… physical instances” is understood as the instantiation of some complex physical property.
VandenHombergh (2017) incorrectly describes Sturgeon’s assumption as an instance of S4, or the transitive 4 axiom. Sturgeon earlier appeals to S4, in order to demonstrate that the possible possibility of a zombie situation entails its possibility, simpliciter—but this concerns his own reconstruction of the conceivability argument, not its mirror.
Indeed, on a technical note, it doesn’t seem to me that the denial of (5) necessitates the existence of a world inaccessible from the actual one. Again, let w@ access w1, w2, w3, and itself, and let these be the only existing worlds. If w1 accesses w2 and w3, while the latter two fail to access one another, then the accessibility relation will be non-Euclidean and the (5) axiom will be invalid—even though, by hypothesis, our world accesses everything.
There are other problems. The conceivability of extrinsic physicalism, as used in the modal mirror argument, requires embedding modal operators in the scope of the conceivability operator, complicating things significantly and contradicting an otherwise plausible hypothesis in modal epistemology (cf. Chalmers’s “modal rationalism” 2002).
With the exception of Campbell et al. (2017), who introduce somewhat distinct background premises to similar effect.
There is one tacit step. The intended interpretation proves the totalized instance of extrinsic physicalism; existentially generalizing gets us the conclusion above.
It might be objected that totalization could obtain in virtue of non-identification; e.g., by way of extrinsic physicalism. But this would clearly embed a necessity operator in the physical situation, therefore regenerating the problems associated with the modal interpretation. Frankish is right to suggest that totalization obtains “in virtue of… token identities”—but this, and not the resulting “metaphysical supervenience,” is what does all the heavy-lifting (2007).
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Acknowledgements
Many thanks to two anonymous reviewers from Erkenntnis, past anonymous reviewers, and colleagues at the University of Wisconsin-Madison (especially Farid Masrour), for criticism and support on earlier drafts of this paper.
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VandenHombergh, J. Consciousness, Conceivability, and Intrinsic Reduction. Erkenn 85, 1129–1151 (2020). https://doi.org/10.1007/s10670-018-0069-6
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DOI: https://doi.org/10.1007/s10670-018-0069-6