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Abstract
Perhaps all concrete phenomena obtain solely in virtue of physical phenomena. Even so, it seems that the world could have been otherwise. It seems that physicalism, if true, is contingently true. In fact, many believe that the actual truth of physicalism allows metaphysically possible worlds duplicating the actual world in all physical respects while containing immaterial extras, e.g. ghosts, spirits, or Cartesian souls, that no physicalist would believe actually exist. Here I focus on physicalism regarding mentality and argue that the doctrine does not allow possible worlds that physically duplicate the actual world while differing mentally. By revealing what physicalism (regarding the mind) does not allow, this essay helps us get clear on what the view really amounts to and why it is contingent.
Notes on Contributor
Robert Francescotti is a graduate of Syracuse University and currently Professor of Philosophy at San Diego State University. His research interests and publications lie mainly in the philosophy of mind (physicalism, supervenience, and animal minds) and metaphysics (the intrinsic/extrinsic distinction, identity, and personhood).
Notes
1. The problem of Extras is designed to show not that physically indistinguishable individuals can differ mentally, but that physically indistinguishable worlds can differ mentally. That is why the emphasis here is on global rather than local supervenience.
2. There are different varieties of global supervenience. Stalnaker (Citation1996) and McLaughlin (Citation1997) distinguish between strong and weak global supervenience. Consider any two possible worlds, w1 and w2, and a one–one mapping of each item x in w1 onto some item y in w2. This isomorphism is φ-preserving for some class of properties, φ, just in case for every property F in φ, Fx in w1 just in case Fy in w2. With the notion of a φ-preserving isomorphism, a class of properties, A, is said to supervene on a class of properties, B, in the strong global sense just in case for any w1 and w2, every B-preserving isomorphism between w1 and w2 is an A-preserving isomorphism between them. A supervenes on B in the weak global sense just in case for any w1 and w2, if there is a B-preserving isomorphism between w1 and w2, then there is an A-preserving isomorphism between them. Bennett (Citation2004) adds a middling variety, which obtains just in case for any w1 and w2, if there is a B-preserving isomorphism between them, then at least one B-preserving isomorphism between them is itself an A-preserving isomorphism; Bennett also shows that the weak variety falls far short of capturing the sort of determination required by our ordinary notion of global supervenience. I leave it open whether the intermediate variety, or the strong, or some other version (Leuenberger's Citation2009 discussion being relevant here) best captures the ordinary notion of global supervenience, since nothing in the following discussion hinges on this issue.
3. The ontological physicalist can consistently believe (with Kirk Citation2006) that the physical facts logically/conceptually necessitate the mental facts. However, as an ontological physicalist one need not (and arguably should not) believe that.
4. Melnyk proposes that “token y of a functional type, F, is physically realized iff (i) y is realized …by a token of some physical type, T; and (ii) T meets the special associated condition for F solely as a logical consequence of (a) the distribution in the world of physical tokens and (b) the holding of physical laws (2006, 130–1)”. This fixing of the higher-level facts by the physical facts is clearly what supervenience claims are designed to report. And one condition in Pereboom's analysis of x materially constituting y is “necessarily, if x exists and is in D at t, then y exists at t and is made up of and materially coincident with x at t” (2011, 140), where D might be the physical features of x on which the distinctive higher-level features of y supervene. Also note that those who advocate some irreducible notion of grounding generally accept the necessity thesis that if one set of facts grounds another, then necessarily if the former obtains, the latter also obtains. See, for example, Correia (Citation2011, 6) and Rosen (Citation2010, 118); and see Fine (Citation2011, 7–8), who replaces talk of necessitation with “relevant verification”.
5. To ensure that the actual physical facts are the same, the Extras we are imagining do not interfere in any way with the operations of the physical world. This assumes that the capacity to interact with the physical world (for instance, to cause the right sort of behaviour) is not essential to mentality. Whether this assumption is correct is an idea I shall here leave entirely open. What I will argue is that even if there could be Extras in physically indistinguishable worlds (and therefore Extras that do not disrupt the physical details), this possibility is not consistent with physicalism.
6. With the notion of a P-world, Horgan offers a local supervenience principle: “[t]here do not exist any two P-regions which are exactly alike in all qualitative intrinsic microphysical features but different in some other qualitative intrinsic feature” (1982, 37).
7. See also Jackson's (Citation1994, 28) presentation of this idea. In the same spirit, Chalmers (Citation1996, 39) characterizes physicalism with an “at least clause” requiring that “at least the B-facts true in our world are true in all physically identical worlds”.
8. See, for example, Witmer's (Citation1999, 321–4) objections to Lewis' proposal. Also see how Witmer (325–9) renders Jackson's appeal to minimal physical duplicates more precise.
9. Kripke introduces the creation metaphor (1972, 340–1) while arguing against the identity of pain and C-fiber stimulation.
10. Apart from the God issue, the creation metaphor might mislead by implying that for the physicalist the initial physical condition of the world determined the rise of mentality and the world's current mental condition. Physicalists clearly need not accept the diachronic necessitation of the mental by the physical, since they need not even accept diachronic physical–physical necessitation (the necessitation of the physical state of the universe at one time by its physical state at a previous time). The point of the metaphor is that for the physicalist, the complete physical condition of the world at any time necessitates the total condition of the world at that time.
11. The universal nature of the fact that all minds are embodied is not itself a reason to deny its necessitation, for there are always universal physical facts, which include the physical laws, to help metaphysically necessitate the universal higher-level facts.
12. Chalmers adds the restriction to positive supervening facts in part to allow the possibility of worlds that physically duplicate the actual world without duplicating, for instance, the actual negative fact that no ghosts are present. Likewise, Melnyk (Citation2003, 26) restricts the domain of quantification of his realization physicalism to tokens that are not of types “partially constituted by absences” – types such as “kind of entity such that every actual member of the kind is physically realized”, whose tokens exist partly in virtue of the non-existence of ectoplasm that serves as a realizer of the kind.
13. The following concern was brought to my attention by one of the referees for Philosophical Explorations. It might be thought that a physically indistinguishable Felicity in a physically indistinguishable world will lack happiness, not because the physical facts necessitate negative mental facts, but because the physical facts necessitate the positive mental fact that Felicity is in some particular mood X, and X is incompatible with happiness just as being red all over is incompatible with being green all over (or any other determinate of a single determinable excludes others). If the case were like this, then it would not be the physical facts themselves that necessitate Felicity's lack of happiness, and so (b) would not be threatened. However, we need not suppose the case is quite like that. Let's suppose that Felicity is not in any mood that excludes happiness in the way that being red all over excludes being green all over. It seems to me that our physicalist intuitions would still entail that any world where Felicity is happy physically differs from the actual world.
14. Thanks to one of the referees for bringing this point about physical interference to my attention.
15. If we follow Chalmers and characterize physicalism in terms of positive facts, then we get the intuitively correct result that physicalism prevents the possibility of the Blockers Hawthorne initially describes. But, Hawthorne notes, Chalmers' characterization of physicalism does not preclude cases in which “only certain mental phenomena – call them M's – are blockable, that Blockers exist, and that all (or some of) the M's that would otherwise have occurred are blocked” (2002, 108–9). Let us also suppose that the Blockers have no mental properties of their own. In this case, any world that physically duplicates the actual world will also have all the positive mental facts obtaining at the actual world. So Chalmers' definition gives the implausible result that physicalism is actually true in this case.
16. Leuenberger (Citation2008) concedes that physicalism is compatible with the possibility of Blockers, and proposes what he calls “ceteris absentibus physicalism”, according to which, “[t]he actual physical facts are ceteris absentibus sufficient for all actual facts” (148). On this account, if a world physically duplicates the actual world, then other things being absent (which includes no Blockers) it mentally duplicates the actual world.
17. Levine and Trogdon (Citation2009) question the contingency of physicalism. They characterize “materialism” as the thesis that “only non-mental properties are instantiated in a basic way; all mental properties are instantiated by being realized by the instantiation of other non-mental properties” (356). Given that causal role properties are non-basic properties and essentially so (essentially realized by the instantiation of other properties, physical properties, playing the definitive causal roles), they contend that mental properties are essentially non-basic, and with their definition of materialism, they conclude that materialism is true in all possible worlds. Yet, their definition of materialism is dubious since (as they realize, 356–7) it allows materialist worlds in which mental properties are realized by ectoplasmic features, provided that these ectoplasmic features are non-mental.