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Interactionist zombies

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Abstract

One of the most popular arguments in favor of dualism is the zombie-conceivability argument. It is often argued that the possibility of zombies would entail that mental properties are epiphenomenal. This paper attempts to defuse the argument, offering an account of dualist mental causation which can serve as a basis for a modified, interactionist-friendly zombie argument.

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Notes

  1. See also Chalmers (2009) and Stoljar (2001). For criticism, see Hill (1997) and Hill and McLaughlin (1999). For recent criticism of conceivability arguments more broadly, see Campbell et al. (2017). See Chalmers (2002) for much more on conceivability and the conceivability-possibility link.

  2. “Non-distinct,” here, is an umbrella term that is meant to capture the ideas that mental and physical properties are identical, that the mental is metaphysically grounded in the physical, and other such proposals that are standardly thought to count as physicalist.

  3. See Balog (1999, 2012). Some, including Frankish (2007), have offered what they take to be conceivability arguments in favor of physicalism, perhaps undermining the force of CONCEIVABILITY ARGUMENT. Baysan and Wildman (2022) also offer a disjunctive account of phenomenal consciousness which they argue undermines both conceivability arguments for dualism and physicalism. Kirk (2008) has offered an argument that zombies are not conceivable.

  4. Perry (2001, 2012) and Bailey (2006, 2009) are central advocates of this argument.

  5. My proposal, as will be seen, is in line with dualists who, in response to the causal exclusion argument popularized by Kim (1998, 2005), deny the causal closure of the physical, such as Lowe (2003) and Won (2021).

  6. On global supervenience, see Bennett (2004).

  7. Carroll (2021) makes an argument in this ballpark, and a similar case regarding the Knowledge Argument is given by Watkins (1989) and Moore (2012).

  8. It should be said that Independence is not obviously true either, because it is conceivable that there be a zombie duplicate of our world which is not the closest non-mental world to actuality. The possibility of a zombie duplicate of the actual world, then, does not immediately entail Independence. I will, however, grant Independence for the sake of argument. One reason for doing this is that Independence may well be true, and it is true for any world with deterministic laws, assuming that the nearest non-mental world is one in which mental properties are subtracted and the physical world is left unchanged with respect to laws and initial conditions. In that case, the deterministic laws will allow only one possible history given the initial physical conditions; so, the zombie-duplicate world would be the unique non-mental world which preserves the physical laws and initial conditions, while also adding no extra non-mental/non-physical properties. Hence, it would be better if an interactionist-friendly conceivability argument can be made consistent with Independence.

  9. Chalmers’ (2004) response to the original challenge is to suggest that our zombie-duplicate world contains unfilled causal gaps. But it is not clear that such a world is physically possible. For one thing, if the laws are deterministic, and the physics of the world is causally closed, then only one future history is possible given the initial conditions. Consequently, if there is any world which evolves to exhibit the same mentalistic behaviors in the absence of phenomenal properties, then those behaviors are nomically necessitated by the initial physical states, irrespective of the instantiation of phenomenal properties. Such physical states, then, would presumably be causally sufficient for the relevant behaviors. Hence, the kinds of worlds that Chalmers posits are either physically impossible—thus requiring a physical difference, namely a difference in the physical laws, in violation of the supervenience requirement—or the mental properties of the actual world are genuinely causally redundant in the sense that the nearest non-mental world to actuality instantiates the same physical properties throughout its entire history. Alternatively, you could put in some extra non-physical and non-mental stuff to close the causal gaps; but this seems to face a similar issue, in that the mental will still supervene on the non-mental, or the non-proto-mental. A more plausible response, which comes from personal communication with Chalmers, might be to restrict the supervenience base to physical properties, excluding physical laws, and make a no-supervenience argument for dualism from there. Such an argument, though, hasn’t been spelled out in the literature, and if my arguments in the next section succeed, it will be unnecessary to restrict the supervenience base in this way.

  10. As I am using it, the semantics for “□ → ” are such that (P □ → Q) is true at w iff there exists a possible (P & Q)-world which is closer to w than any (P & ~ Q)-world.

  11. For this reason, in fact, dualists may find even The Minimal Criterion to be too strong—see Vaassen (2019). However, as I will show, dualists need not deny The Minimal Criterion, and maintaining it will allow for a more robust picture of dualist mental causation.

  12. Of course, this is only going to be a necessary condition for dualist mental causation, since physicalists will hold not just that the antecedent is nomically impossible, but also metaphysically impossible. The resultant counterpossible may be trivially true—depending on how you prefer to assess counterpossibles—but it wouldn’t be true in any interesting sense for mental causation.

  13. See Kroedel (2015), though, for dissent.

  14. For instance, see Kroedel (2008), Moore (2009), McDermott (2002), Hitchcock (2007), and Halpern and Pearl (2005) on Symmetric Overdetermination and the corresponding problem for Lewis’ account. See also Hitchcock (2001) for an interventionist account of causation which, like Lewis’ account, is counterfactual in nature, but which, unlike Lewis’ account, handles causal overdetermination. See also Sider (2003) for more on why we generally should allow for causal overdetermination.

  15. See also Loewer (2001).

  16. For a sample of the physical and philosophical literature on CSTM, see Feynman (1967, ch. 5), Brown and Uffink (2001), Uffink (2001), Loewer (2012), Callender (1997, 2011), Cohen and Callender (2010), Frisch (2010), Leeds (2003), North (2011), Weslake (2014), and Winsberg (2004).

  17. See Chen (2021) and Chen and Tumulka (2022) for more on this.

  18. See Brown et al. (2009), Davies (1974), and Sklar (1993) for more on the Reversibility Objection.

  19. For literature on CSTM and the low-entropy boundary condition in postulate (iii), see Penrose (1994), Callender (2004a, 2004b), Frigg (2009a, 2009b), Goldstein (2001), and Parker (2005).

  20. The colorful examples are due to Albert (2015).

  21. For vividness, one may imagine a world that is macroscopically just like the actual world throughout its entire history, but which is just filled, slice-by-slice, with these thermodynamic miracles.

  22. Less obvious, perhaps, is that the causal chains in w* and w*Z are realized in a microphysically identical way. Might the presence of PAIN(x), when instantiated, still make some difference to the underlying micro-state, despite realizing the same causal chain from a macroscopic perspective? I have in mind, however, an interaction law which is higher-order, i.e. where the nomic connections are between states like PAIN(x) and MOTOR(x), rather than one on which PAIN(x) necessitates any precise changes in the micro-dynamics. And then a natural assumption—arguably in line with scientific practice, is a kind of principle of least action, which intuitively says that a given dynamical transition will keep the change in a system’s energy distribution to a minimum, as the system is moved from one point to another. Formally, this means minimizing what is called the action functional, which is the integral ∫(T–V)dt, where T is kinetic energy and V is potential energy. We might plausibly assume something fairly analogous about our interaction laws, namely that PAIN(x) makes the smallest possible alteration in the particle trajectories (thereby keeping its difference to the energy distribution of a system to a minimum) in order to realize the target macro-physical state, relative to the trajectory that would have occurred in the absence of PAIN(x). But in fact all one really needs is for the interaction law not to be maximally biased against least action, i.e. by not requiring that the phenomenal states always make a microphysical difference when the microphysics suffice. As long as they do not always make a microphysical difference in the face of already-sufficient initial conditions, there will be some world pairs our there, like w* and w*Z, where the microphysics is identical between the two worlds.

  23. Thanks to an anonymous reviewer for pushing me to clarify this point.

  24. As noted in the previous subsection, CSTM is not itself the correct physical theory of our world, but this is only because the first postulate needs to be replaced with some non-classical laws of motion, such as the Schrodinger Equation. Nothing said here would be undermined by this replacement.

  25. Strictly speaking, my arguments could do without this: the argument would still work if, say, I had appealed to worlds which are not physically possible with respect to our laws, but which are physically possible with respect to each other. However, the argument is stronger if the relevant worlds are actually physically possible, in part because the argument can now be accepted by those who believe that the actual laws of physics are metaphysically necessary.

  26. Thanks again to an anonymous referee for this point.

  27. Mohammadian’s discussion targets Quantum Collapse Interactionism (QCI), the view that consciousness collapses quantum wavefunctions. The following worry does apply, I think, to QCI, where I think Mohammadian is right on point. But, as I attempt to show, it won’t apply generally to views which posit a different kind of interaction law for mental properties.

  28. □, here, is a nomic necessity-operator, rather than a metaphysical necessity-operator.

  29. See, e.g., Loewer (1996) and Lange (2000) for more on these characteristics of laws.

  30. See Vaassen (2022) for why this might matter to their causal status.

  31. Though, see other strategies from Vaassen (2019, 2021), Kroedel (2015, 2020), and Bealer (2007).

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Acknowledgements

Many thanks to two anonymous referees at Synthese, Brian McLaughlin, and especially Bram Vaassen, for many helpful comments on earlier drafts of this paper.

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    Jake Khawaja

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Khawaja, J. Interactionist zombies. Synthese 200, 489 (2022). https://doi.org/10.1007/s11229-022-03970-x

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