Grounding, mental causation, and overdetermination


Recently, Kroedel and Schulz have argued that the exclusion problem—which states that certain forms of non-reductive physicalism about the mental are committed to systematic and objectionable causal overdetermination—can be solved by appealing to grounding. Specifically, they defend a principle that links the causal relations of grounded mental events to those of grounding physical events, arguing that this renders mental–physical causal overdetermination unproblematic. Here, we contest Kroedel and Schulz’s result. We argue that their causal-grounding principle is undermotivated, if not outright false. In particular, we contend that the principle has plausible counterexamples, resulting from the fact that some mental states are not fully grounded by goings on ‘in our heads’ but also require external factors to be included in their full grounds. We draw the sceptical conclusion that it remains unclear whether non-reductive physicalists can plausibly respond to the exclusion argument by appealing to considerations of grounding.

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  1. 1.

    See Kim (1989, 1993) and Malcolm (1968); for an overview of the debate, see Heil and Robb (2014: § 6.2).

  2. 2.

    For the charge that grounding is not theoretically fruitful, see Koslicki (2015) and Wilson (2014).

  3. 3.

    Thanks to an anonymous referee for helpful discussion of this point.

  4. 4.

    We have reformulated Non-Reduction, as well as the other key principles of Kroedel and Schulz’s discussion, in terms of property instances. Given our (and their) usage, this does not alter the content of these principles. Thanks to an anonymous referee for this suggestion.

  5. 5.

    Note that Grounding could be weakened by dropping the necessity operator; however, we’ll set this complication aside here.

  6. 6.

    This sketch, of course, simplifies the problem. For one thing, it does not specify necessary or sufficient conditions for overdetermination. Kroedel and Schulz distinguish two concepts of overdetermination (2016: pp. 1918–19): c1 and c2 strongly overdetermine event e iff c1 and c1 are (1) distinct, (2) both causes of e, (3) causally independent, and (4) metaphysically independent. Meanwhile, c1 and c2 weakly overdetermine e iff c1 and c2 are (1) distinct, (2) both causes of e, and (3) causally independent. Arguably, both concepts require a clause to the effect that c1 and c2 are events of the same type; see e.g. Dretske (1988: p. 42ff) and Jaworski (2016: p. 280 ff). Thanks to an anonymous referee here.

  7. 7.

    Kroedel and Schulz suggest that Exclusion is a plausible generalisation, deriving

    its initial plausibility from the observation that cases of overdetermination do not seem to abound in other areas of the physical world, which strongly suggests that they do not abound where there is mental causation either (2016: p. 1916).

    We doubt that this is the source of Exclusion’s plausibility. Belief in composite objects arguably brings commitment to systematic overdetermination by these and their parts, and an analogue to the exclusion problem arises in this context (see Merricks 2001). Since this composition-overdetermination debate is on going, it is premature to claim that cases of overdetermination aren’t abundant in other areas. Moreover, since Exclusion and its analogue in the composition debate are of a piece, it is implausible that the former borrows its plausibility from the latter. Both principles stand in need of independent motivation; perhaps the parsimony considerations we sketch in the text can play this role.

  8. 8.

    Strictly speaking, they offer non-reductive physicalists a choice: either reject Exclusion or reject the claim that there is genuine overdetermination between the mental and the physical. Their central claim is that Grounding is helpful, and perhaps indispensible, for implementing either strategy.

  9. 9.

    Thanks to an anonymous referee for help in clarifying this paragraph.

  10. 10.

    More precisely, because m is not metaphysically independent of p, m and p do not strongly overdetermine e. Meanwhile, though m and p weakly overdetermine e, the grounding connection between m’s causing e and p’s causing e allows us to ‘give a principled explanation of why the physical effects of mental events are weakly overdetermined’ meaning grounding physicalism can ‘dispel the worry that the overdetermination of the physical effects of mental causes is a surprising coincidence’ (Kroedel and Schulz 2016: p. 1920).

  11. 11.

    For further discussion about material constitution, see e.g. Paul (2010), Bennett (2004) and Koslicki (2004, 2008).

  12. 12.

    Though see Wildman (ms) for discussion of this point.

  13. 13.

    This point is closely related to the grounding puzzle. For further discussion, see Zimmerman (1995), Bennett (2004), and Simons (1987).

  14. 14.

    Interestingly, Kroedel and Schulz claim that CG ‘merely says that if a mental event possesses properties of causing such-and-such physical events, then they are due to a physical event that grounds the mental event’ (2016: p. 1914). But this wouldn’t be CG—rather, it would be the weaker


    Let m be a mental event, and let e be a physical effect of m. Then there is a physical event p such that p’s existence grounds m’s existence and m’s causing e is grounded in something about p

    And WCG is just another version of the (effectively worthless) promissory note, as it doesn’t tell us what the relevant physical grounds are.

  15. 15.

    We adopt the convention of using square brackets to denote facts, so that ‘[P]’ is to be read: the fact that P.

  16. 16.

    We assume that [17 is prime] is not fully grounded by concreta, but this is dispensable for the argument. Even if [17 is prime] is grounded by concreta, it is—to say the least—hard to be confident that these concrete grounds will be causally linked to me in the systematic manner which CG predicts.

  17. 17.

    This involves the simplification that Star alone causes Wow, when realistically Star would only cause Wow in conjunction with other mental events; but this does not seem to crucially affect the point of the example.

  18. 18.

    This reasoning does not require the dubious claim that we can have singular thoughts about stars outside our light cone. It does assume that any ground for an existential generalisation will either be, or will ground, some of its instances; see Fine (2012: p. 65).

  19. 19.

    It is noteworthy that part of the motivation Kroedel and Schulz cite for their account of mental causation is that it preserves intuitive causal ascriptions; see their fn. 30.

  20. 20.

    Classic defences of externalist accounts of content include Burge (1979) and Putnam (1975).

  21. 21.

    Again, the problem can be made more vivid by appealing to beliefs about abstract or distant entities.


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This paper has benefitted from discussion with audiences at the Eidos seminar in Geneva and Hamburg’s Forschungskolloquium. We are especially grateful to Delia Belleri, Amanda Cawston, Donnchadh O’Connaill, Thomas Kroedel, Giovanni Merlo, and Moritz Schulz for extensive discussion and feedback. This paper was written partially under the auspices of the Sinergia project Grounding: Metaphysics, Science, and Logic, which is funded by the Swiss National Sciences Foundation; we gratefully acknowledge their support.

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Clark, M.J., Wildman, N. Grounding, mental causation, and overdetermination. Synthese 195, 3723–3733 (2018).

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  • Grounding
  • Mental causation
  • Overdetermination
  • Causal exclusion