Posted by: Xhyra Graf | 28 January 2007

Mental Causation

Mind-body causation is problematic for a substance dualist, but it appears to be less so for a materialist, someone who believes that the mind, if it is a substance at all, is a material substance such as the brain. While causation between brain and body can be quite complex, even to the point of being empirically inscrutable, it does not pose the same problems as soul-body interaction does: there are no philosophical problems with a brain-body causal nexus that are not general to the notion of a causal nexus.

However, even if the mind is the brain or some other physical substance, mental causation remains puzzling. Theoretical and commonsensical considerations leading us to think the mind causes behavior should also make us think that it does so in virtue of its mental properties.

A rock causes a nasty bump on my head qua thing of a certain mass. And it is qua mental — that is, in virtue of their mental properties — that minds cause behavior.

Recent philosophical work on mental properties has revealed that matters are not so simple, however. Mental properties are alleged to have, not just one, but up to four features that make their causal relevance philosophically puzzling, no less problematic than mind-body interaction is for the substance dualist. These features, to be discussed in the following four sections, are ontological distinctness, anomalousness, multiple realizability, and externality. Each of them makes it appear as though mental properties, or some subset of them, are causally irrelevant to behavior: the mental never causes anything qua mental.

One version of the property-based problem arises immediately for those philosophers who believe that, even if mental substances are physical, mental properties are not. “Property dualism” has several contemporary defenders, including David Chalmers (1996) and at one time Frank Jackson (1982, 1986; but see his 1998, forthcoming). For the property dualist, mental properties — and here the mental properties taking center stage are the phenomenal properties of conscious experience — are sui generis, not reducible to the dispositional or structural properties recognized by the physical sciences (see dualism).

If mental properties are non-physical in this way, it seems that they could not be causally relevant to physical happenings. [Epiphenomenalism]

We have good reason to think that every physical event has a physical cause. So non-physical mental properties can be causally relevant to what our bodies do only by working together with physical properties to overdetermine behavior. But this sort of systematic mental-physical overdetermination has struck many as implausible, even as absurd.

Completeness: Every physical event has a sufficient physical cause.

Completeness also at times goes under the name of “Closure”, though some (cf. Kim 1998, p. 40; Robb 1997) prefer to reserve this latter term for a stronger principle, one entailed by Completeness plus a ban on overdetermination.

Is Completeness true? Some may take it to be an an analytic truth, one falling out of the very concept of the physical.

Alternatively, a less ambitious defense of Completeness may claim that it’s merely a working hypothesis of natural science or a principle presupposed by physicalism, a philosophical doctrine that enjoys independent support (cf. Lewis 1966, p. 23; Kim 1993a, p. 290). In any case, the truth of Completeness, not to mention its proper formulation, is still very much a live philosophical issue.

No Overdetermination: There is no systematic overdetermination of physical events.

This principle allows some physical events to be overdetermined. Perhaps, for example, both the loudness and the suddenness of a thunderclap are causally sufficient for my jumping. But if a mental and a physical property were causally relevant to every behavioral event, this would be a pervasive, systematic overdetermination of a significant subset of physical events. No Overdetermination is meant to rule this out.

According to many functionalists, mental properties are functional properties (Putnam 1967; Fodor 1968, 1975; Block 1980b; Heil 1998, ch. 4). To be in pain, for example, is a matter of being in a state with a certain causal profile: pain is a state caused by tissue damage, and one that causes certain overt responses (moans, attempts to repair the damage, beliefs that one is in pain). But, argue functionalists, it is unlikely that we could find a single physical state that played this role in every actual and possible case of pain. Human beings differ in subtle physiological ways: one person’s neurological states, including states he goes into when he is in pain, differ subtly from another person’s. Human beings’ neurological states, in turn, differ from those of a cat or a dog, and perhaps dramatically from states of an octopus. We can even imagine encountering aliens with vastly different biologies, but to which we would unhesitatingly ascribe pains.Here we arrive at a core thesis of functionalism: states of mind are “multiply realizable“. The property of being in pain can be realized in a wide variety of physical (and perhaps non-physical) systems. Someone is in pain in virtue of being in a state with the right sort of causal profile, some sort of neurological state, say. But the property of being in pain cannot be identified with this neurological state because creatures of other kinds can be in pain in virtue of being in vastly different physical conditions. (For further discussion of this argument, see Kim 1992; Heil 1999.) Functionalists often put this point by saying that mental properties are “higher-level” properties, properties possessed by objects by virtue of their possession of appropriate “lower-level” properties, their realizers.

  • 7. Problem IV: Externalism

    The final version of the property-based problem we’ll look at is restricted to intentional mental properties. Suppose, as many philosophers do, that externalism is true: the contents of representational states of mind — propositional attitudes, perceptual experiences, mental images, and so on — depend, not on intrinsic features of those states, but on relations; in particular, they depend on the causal, historical, and social relations agents bear to their surroundings. (For a discussion of motivations for externalism, see Putnam 1975a; Burge 1979, 1986; Heil 1992, chap. 2; mental content: externalism about.) In the simplest case, Lilian’s thoughts about water are thoughts about water (H2O) because Lilian stands in the right sorts of causal relations to water. The key move here is to reject the idea that meaningful objects or states owe their meaning to their intrinsic make-up

    Narrow content could be thought of as the content of a representational state of mind minus its “broad” components. Consider Lilian (or Lilian’s brain) and an intrinsically indiscernible brain in a vat wired to a supercomputer. Grant that Lilian and the envatted brain entertain intrinsically indiscernible thoughts with utterly different representational contents. Now imagine that we could abstract a common element from the contents of Lilian’s and the brain’s intrinsically indiscernible thoughts. This element is their narrow content. Because narrow content is something all intrinsic duplicates must have in common, the hope is that such content could have a role in producing behavior.

    A second, quite different, attempt to preserve the causal relevance of intentional properties can be found in the work of Fred Dretske (1988, 1993). So far we’ve assumed that a behavioral event is distinct from the mental event that causes it. But on Dretske’s view, behavior is a process that includes, as a component, its mental cause. When mental event a causes bodily movement b, the behavior in this case is not b itself, but the process of a‘s causing b. For example, when Lilian raises her hand because she wants to get the teacher’s attention and she believes that raising her hand will accomplish this, her behavior is not her hand’s going up, but the process of this belief-desire pair’s causing her hand to go up. Now Dretske grants that when mental event a initiates, or “triggers”, a process ending in bodily movement b, a does so only in virtue of its instrinsic properties. Neverthess, a‘s relational, intentional properties have a causal role, for they can be relevant to the fact that a causes b. Dretske puts this point by saying that reasons are “structuring” causes of behavior: it’s because of what a indicates that it was “recruited” during the learning process as a cause of b. It’s because, for example, that Lilian’s belief indicates what it does — raising one’s hand (in these circumstances) is a way to get the teacher’s attention — that it was recruited as (together with the relevant desire) a cause of hand-raising. Relational, intentional mental properties thus become causally relevant to behavior, since they are relevant to structuring the very causal processes that, on Dretske’s view, are instances of behavior.

    Dretske’s solution to the externalist problem is an original, intriguing position, though it raises a number of questions (see, e.g., Kim 1991; Block 1990, pp. 153-4). One question is whether relational, intentional properties do in fact play a causal role in the structuring (or “wiring”) of causal processes in the brain.

    Dretske’s proposal is a version of what’s sometimes called the “dual explanandum” strategy. The idea is that physical and mental properties are causally responsible for different effects. For Dretske, the (triggering) physical properties are responsible for bodily movement, while the (structuring) mental properties are responsible for behavior.

    • Because it promises to solve two problems of mental causation, this approach is potentially quite powerful. (For discussion, see Fodor 1991a; Burge 1995.) One question to raise here, however, is whether the fact that some behavior can be described broadly makes the intentional mental property of its cause relevant. The undeniable conceptual connections between mental and behavioral descriptions may point to a kind of explanatory relevance, but it’s a further question as to whether the causal connections grounding these explanations involve broad properties. Those motivated by the original epiphenomenalist arguments will worry that narrow, physical properties are doing all of the causal work here: the apparent relevance of the broad properties is an illusion created by the way we, in explaining behavior, conceptualize both cause and effect
  • Some would challenge the distinction between explanation and causation, insisting that our concept of causality is fundamentally explanatory: causally relevant properties are those that figure in our best causal explanations (Burge 1993; Baker 1993). We find out what causal relations amount to by starting with cases of causal explanation. We (and cognitive scientists) routinely explain physical events by citing mental causes (and vice versa). To question whether real causal relations answer to these explanations is to succumb to metaphysical hubris. This appeal to explanatory practice has the potential to answer all four of the property-based problems we’ve looked at.

    No doubt our understanding of the notions of causality and causal relevance depends on our grasp of causal explanations. But there are at least two areas of concern about this explanatory strategy (cf. Kim 1998, pp. 60-7): First, is it addressing the right question? Earlier, we pointed out that the central question of mental causation is not so much whether mental properties are causally relevant but how they could be, given some alleged feature of mental properties (in this case the feature is their being relational properties). The explanatory strategy would at best seem to be addressing only the “whether” question, not the “how” question. Second, even when restricted to the “whether” question, the strategy does rest on a conflation of what appears to be an epistemological notion (explanation) with metaphysical notions (causation and causal relevance). A full evaluation of the view thus requires a deeper look into how the two are related.

  • 8. Metaphysics and the Philosophy of Mind

We conclude with a methodological question. The foregoing discussion of mental causation has raised a number of fundamental metaphysical issues concerning, for example, laws, counterfactuals, causality, and properties. Does making progress on the problem of mental causation, and in the philosophy of mind generally, really require philosophers to delve into foundational metaphysics?

One way to bring this question into focus is to consider Georges Rey’s “Fairness Maxim for the Philosophy of Mind”:

DON’T BURDEN THE MIND WITH EVERYONE ELSE’S PROBLEMS. Always ask whether a problem is peculiar to the mind, or whether the issue could equally well be raised in other less problematic areas. If it can be, settle it for those areas first, and then assess the philosophy of mind (Rey 1997, p. 27).

Some philosophers of mind might read the principle as advice to remain neutral on metaphysical matters such as those listed above. But one risk of the practice of neutrality is that seemingly innocent assumptions — e.g., that counterfactuals reveal causal connections, or that a given predicate picks out a genuine property — can in fact embody substantive metaphysical theses. But another way to read Rey’s principle is as a statement of the proper order of inquiry: Foundational, metaphysical questions should be addressed prior to questions about the mind, in such a way that metaphysics informs one’s philosophy of mind. Philosophers following this advice can avoid pursuing solutions to the problem of mental causation that are tailored to a favored thesis in philosophy of mind; such solutions are in danger of appearing ad hoc from a broader metaphysical perspective. The aim instead would be an account of mental causation that generalizes smoothly across the board, and for that reason is more powerful.


Robb, David, Heil, John, “Mental Causation”, The Stanford Encyclopedia of Philosophy (Spring 2005 Edition), Edward N. Zalta (ed.), URL =


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