Problem of mental causation

The problem of mental causation is a conceptual issue in the philosophy of mind. That problem, in short, is how to account for the common-sense idea that intentional thoughts or intentional mental states are causes of intentional actions. The problem divides into several distinct sub-problems, including the problem of causal exclusion, the problem of anomalism, and the problem of externalism. However, the sub-problem which has attracted most attention in the philosophical literature is arguably the exclusion problem.

The general problem

The basic problem of mental causation is an intuitive one: on the face of it, it seems that mental events cause physical events (and vice versa), but how can mental events have any causal effect on physical events? Suppose, for example, some person, John, orders dessert after dinner. It seems that at least one cause for such a physical, behavioral event is that John desired to have dessert and believed that by ordering dessert he would be able to soon have dessert. But, how can such mental events as beliefs and desires cause John's mouth to move in such a way that he orders dessert?

Sub-problems of mental causation

Exclusion problem

What follows is a summary of the causal exclusion problem in its simplest form, and it is merely one of several possible formulations.

To the extent that we do not have to go outside human physiology in order to trace the causal antecedents of any bodily movement, intentional action can be fully causally explained by the existence of these physiological antecedents alone. No mention of mental states need enter into the explanation. This troubles philosophers because, pre-theoretically, it seems that what is crucial in causing a person to act is their mental states (for example, their beliefs and desires). But, given that physiological facts are sufficient to account for action, mental states appear to be superfluous; they are at risk of being causally and explanatorily irrelevant with respect to human action (Yoo 2007, §3b.iii).

Many consider this to be a highly counter-intuitive and undesirable position to take. It ultimately leads to epiphenomenalism--the view that mental events or states are causally irrelevant, they are merely after effects that play no role in any causal chains whatsoever. Thomas Huxley famously noted that epiphenomenalism treats mental states like the steam coming off a train: it plays no causal role in the train's moving forward, it is merely an "emergent property" of the actual causation occurring in the engine (Walter 2007, §2).

Problem of anomalism

Another problem with mental causation is that mental events seem anomalous in the sense that there are no scientific laws that mental states can figure into without having exceptions. There are no "strict" laws, and mental events must factor into strict laws in order to fit respectably into the causal order described by current science (see Davidson 1970).

In short, one response has been to deny that psychological laws involving mental states require strict, exceptionless laws. Jerry Fodor (1980) argues that non-basic (or "special") sciences do not in fact require strict laws. In current practice, special sciences (for example, biology and chemistry) have ceteris paribus laws (or laws with "all else being equal" clauses), according to which there are exceptions. However, only in the basic sciences (physics) are there strict, exceptionless laws. Thus, although mental states are anomalous, they can still figure into scientifically respectable laws of psychology.

Problem of externalism

In the latter half of the twentieth century externalism about meaning became espoused by many philosophers. Externalism is roughly the view that certain parts of an individual's environment play a crucial role in the meaning of at least some of an individual's words (see Putnam 1975 and Burge 1979). A thesis about meaning affects the mind insofar as our thoughts are about things in the world. A common view in the philosophy of mind is that at least certain mental states have intentional content in this sense. For example, one's belief that water is wet has the semantic content of water is wet. The thought is about water and the fact that it is wet. But, if externalism is true—if some of the contents of one's thoughts are constituted at least in part by factors external to one's mind—then there is yet another difficulty in explaining how mental states can cause physical states (see Yoo 2006, §3b.ii).

Solutions to the problem

Dualist solutions

There are several options for answers to the kinds of questions raised by the basic problem of mental causation. One can simply claim that while the mental and the physical are quite different things, they can nonetheless causally interact with one another. This view is known as interactionist dualism. According to such a view, mental events and physical events are entirely different things. One main difference is that mental events have no spatial location, yet physical events do. However, the two causally interact nevertheless (see Descartes 1642/1986, especially meditations II & VI).

The major problem that interactionist dualism faces is that of explicating a satisfactory notion of causation according to which non-spatial events, such as mental events, can causally interact with spatially located events. According to the current mainstream scientific world-view, the physical realm is causally closed in that causal relationships only hold among physical events in the physical realm. Given these types of considerations, some argue that it is appropriate to say that the main assumptions in interactionist dualism generate the problem of mental causation rather than solve it (see Yoo 2006, §1a).

Physicalist solutions

The other major option is to deny that mental events are non-physical. Views that fall under this general heading are called physicalism or materialism. But, such views require a particular theory of how mental events are physical in nature. One such theory is behaviorism. Behaviorists, in general, argue that mental events are merely dispositions to behave in certain ways. Another theory is the identity theory, according to which mental events are (either type- or token-) identical to physical events. A more recent view, known as functionalism, claims that mental events are individuated (or constituted by) the causal role they play. As such, mental events would fit directly into the causal realm, as they are simply certain causal (or functional) roles. Finally, there is eliminative materialism, which simply denies that there are any such mental events; thus, there is really no problem of mental causation at all.

References & further reading

• Burge, Tyler (1979). "Individualism and the Mental," Midwest Studies in Philosophy, Vol. 4, pp. 73-121.
• Dardis, Anthony (2008). Mental Causation: The Mind-Body Problem. New York: Columbia University Press. ISBN 0231144172.  (link)
• Davidson, Donald (1970). "Mental Events," reprinted in Davidson (1980), pp. 207-227.
• Davidson, Donald (1980). Essays on Actions and Events, Oxford: Clarendon Press.
• Descartes, René (1642/1986). Meditations on First Philosophy, translated by John Cottingham, Cambridge: Cambridge University Press.
• Heil, John; and Alfred Mele (eds.) (1993). Mental Causation. Oxford: Clarendon Press. ISBN 0-19-823929-7. 
• Jackson, Frank (1982). "Epiphenomenal Qualia," Philosophical Quarterly, Vol. 32, pp. 127-36.
• Jaegwon Kim (1998). Mind in a Physical World: An Essay on the Mind-Body Problem and Mental Causation. Cambridge, Mass.: MIT Press. ISBN 0-262-11234-5. 
• Putnam, Hilary (1975). "The Meaning of 'Meaning'", in Putnam's Mind, Language and Reality: Philosophical Papers 2, 1975, Cambridge: Cambridge University Press, pp. 215-71.
• Robb, David (2003). "Mental Causation," The Stanford Encyclopedia of Philosophy, Edward Zalta (ed.). (link)
• Walter, Sven; and Heinz-Dieter Heckmann (eds.) (2003). Physicalism and Mental Causation. Exeter, England: Imprint Academic. ISBN 0-907845-47-9. 
• Yablo, Stephen (1992). "Mental Causation," The Philosophical Review, Vol. 101, No. 2, pp. 245-280.
• Yoo, Julie (2006). "Mental Causation," The Internet Encyclopedia of Philosophy, James Fieser and Bradley Dowden (eds.). (link)