Abstract
This paper argues that the exclusion problem for mental causation can be solved by a variant of non-reductive physicalism that takes the mental not merely to supervene on, but to be grounded in, the physical. A grounding relation between events can be used to establish a principle that links the causal relations of grounded events to those of grounding events. Given this principle, mental events and their physical grounds either do not count as overdetermining physical effects, or they do so in a way that is not objectionable.
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Notes
Compare (Kim 2005, pp. 33–34). For Kim, the non-reductive character of the position consists in the claim that mental properties are neither reducible to nor identical with physical properties. For simplicity, we take non-identity to entail non-reducibility. Whether supervenience suffices for physicalism has been a matter of some controversy (see Horgan 1993 and Wilson 2005 for arguments against the sufficiency; for replies, see Howell 2009 and Kim 2011). It is common in the debate about the exclusion problem to ignore problems with the sufficiency of supervenience for physicalism. We shall follow this practice, because our ultimate concern is the comparative merits of the supervenience and grounding relations rather than the characterisation of physicalism.
See Steinberg (2013) for a detailed survey of the various existing notions of supervenience and their logical relations.
As it stands, our characterisation of non-reductive physicalism makes it metaphysically necessary if true. If one preferred a characterisation that allows non-reductive physicalism to be contingent, one could restrict the universal quantifiers over mental properties to mental properties that are actually instantiated. This would yield the contingency of non-reductive physicalism on the assumption that (i) some mental properties are not actually instantiated and (ii) some of those mental properties fail to supervene on physical properties in some worlds where they are instantiated. Similarly for our formulation of Grounding Physicalism below.
In the context of the philosophy of mind, see, for example, the recent paper by Barnes (2012). Wilson (2014) holds that non-modal relations of relative fundamentality have taken centre stage for non-reductive physicalists for quite some time, albeit in the form of relations more specific than grounding, such as the realizer-realizee relation or the determinate-determinable relation.
Alternatively, one could take facts to be the relata of causation, as Mellor (1995) does, or allow for grounding between events.
Those readers who prefer a different account of events, but acknowledge that there can also be causal relations between property instances, may interpret the remainder of the paper as discussing causal relations between property instances.
Compare Schaffer (2009), who allows entities that belong to different ontological categories to enter the grounding relation.
Yablo (1992) holds that the psychophysical relation is that between determinables and determinates. If the relation between determinables and determinates is an instance of the grounding relation (as Rosen 2010 argues), Yablo counts as an adherent of Grounding Physicalism. Grounding Physicalism need not assume that the psychophysical relation is that between determinables and determinates, however, so it is not touched by objections, such as those of Funkhouser (2006), to Yablo’s specific account. Similar remarks would apply to Shoemaker’s (2007) conception of physical realization to the extent that it can be taken to be a species of the grounding relation. Since Grounding Physicalism as we have formulated it is not a physicalist thesis about everything, the question of whether and how the grounding facts themselves are grounded need not concern us here, but see Sider (2011) and Dasgupta (2014) for discussion.
Strictly speaking, this leaves open the possibility that a given mental property instance is identical to a physical property instance distinct from any of the physical property instances that ground it. This possibility seems implausible to us, but should it turn out to be a live option after all, we could always fall back on characterising Grounding Physicalism inter alia by Non-Reduction. Further, the inference from a difference of the property instances to a difference of the corresponding properties (in terms of which Non-Reductionism is characterised) requires that the property instances be different because of their property component and not only because of a difference in the instantiating objects. Again, we take the latter possibility to be implausible.
The parenthetical qualification is needed because certain highly unspecific properties such as being self-identical may be possessed by grounded entities independently of their grounds.
Ney (unpublished-a, unpublished-b) applies Fine’s (2001) framework of ground and factuality to causation in general and to mental causation in particular, arguing that derivative causal claims, including claims about mental causation, may either be real or unreal depending on whether they tightly correspond to a fundamental physical process or additionally invoke facts about counterfactual dependence. Given that for Ney unreal causal facts are grounded in more than physical processes, she might not be inclined to endorse a principle akin to Causal Grounding, though it is clear that she is sympathetic to its overall spirit. Kim (2005, p. 20), on the other hand, endorses a principle similar to, but significantly stronger than, Causal Grounding that is formulated in terms of supervenience rather than grounding.
This flexibility could help to dispel worries that Causal Grounding might be in tension with Yablo’s proportionality constraint (1992, pp. 277–279).
One could also consider further weakenings of the principle (for one suggestion see the following footnote), which might disentangle the physical event which grounds the mental event from the physical event which causes the physical effect of the mental event. But we decided to work with a principle which stays closest, in our eyes, to the idea that the causal properties of mental events are passed on to them via the grounding relation.
It would suffice for our purposes in the following sections to endorse, instead of Causal Grounding, the following weaker, but somewhat less intuitive, principle:
Weak Causal Grounding. Let m be a mental event that is grounded by physical event p. Let e be a physical effect of m, and let p cause e. Then m causes e because p causes e.
Unlike Causal Grounding, Weak Causal Grounding does not entail Double Causation, so anyone who is sceptical about Double Causation but sympathetic to the general idea that the causal properties of mental events are grounded could still accept the solution to the overdetermination problem that we shall present.
For an overview of the recent debate about the overdetermination problem, see Bennett (2007).
Sometimes the causal independence of two events a and b is defined as follows: a does not cause b; b does not cause a; and a and b do not have a common cause. Friends of this definition could re-label the notion we have defined as, say, ‘conditional causal independence’, which would yield an analogy to the distinction between statistical independence and conditional statistical independence.
Carey (2011, p. 255) makes a similar point.
Let us point out that what we define here is a notion of event overdetermination. Sider (2003) also allows entities belonging to other ontological categories, such as physical objects and facts, to enter the relation of causation. Our definition is not meant to cover this. If one were to broaden it, one might have to revisit our definition of metaphysical dependence in terms of grounding, for it could then be the case that both the event of a given object a’s being F and the fact that a is F have a common effect without the event’s grounding the fact or vice versa (they may have a common ground, though). On the assumption that the event and the corresponding fact are distinct, one would not want to count such a case as a case of overdetermination.
Bennett (2008, p. 289, n. 13) discusses a similar case (albeit in a different context) and commits herself to the possibility of cases of overdetermination where the overdetermining events have a common cause.
The answer to the question would be unambiguously positive if, instead of the three-place predicate ‘\(c_{1}\) and \(c_{2}\) (strongly) overdetermine e’, one explicitly used the one-place predicate ‘e is (strongly) overdetermined’ and defined the latter to be satisfied if and only if there are events \(c_{1}\) and \(c_{2}\) such that \(c_{1}\) and \(c_{2}\) (strongly) overdetermine e. The scope of the existential quantifier in the truth-conditions of this one-place predicate is likely to be subject to contextual restrictions, however, a detailed discussion of which would go beyond the scope of this paper.
On causation and simultaneity in quantum mechanics, see Fenton-Glynn and Kroedel (2015).
On a similar issue, see Sider (2003).
Admittedly, our claim that weak overdetermination is prevalent rests on cases involving causal relationships between events involving macroscopic composites such as armies or persons. Hence, it will not have much force against proponents of the view that such objects do not exist. As a matter of fact, Merricks (2001) uses precisely a variant of the exclusion argument to bolster this kind of eliminativism (somewhat curiously, though, he allows for the existence of one kind of macroscopic objects, namely persons). We contend, however, that the existence of macroscopic objects is prima facie the more plausible view as it does justice to more of our pretheoretic assumptions. As a result, we do not think that presupposing the existence of macroscopic objects constitutes a petitio principii. For a critical discussion of Merricks’s generalization of the exclusion argument, see Sider (2003).
For instance, properties that are necessarily instantiated by everything, such as being self-identical, supervene on, but are not grounded in, any other property. For further discussion, see Steinberg (2013).
Indeed, Fine (2001, p. 15) holds that grounding is the most intimate (“the tightest”) explanatory relation.
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Acknowledgments
We would like to thank Luke Fenton-Glynn, Alexander Skiles, Alexander Steinberg, two anonymous referees for Synthese, and audiences and workshop participants in Barcelona, Berlin, Hamburg and Paris for helpful comments and suggestions.
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Kroedel, T., Schulz, M. Grounding mental causation. Synthese 193, 1909–1923 (2016). https://doi.org/10.1007/s11229-015-0820-3
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DOI: https://doi.org/10.1007/s11229-015-0820-3