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 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?

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 intuitively it seems that mental states are crucial in causing a person to act (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 2006, p. §3b.iii).

Many philosophers consider this apparent irrelevance 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 2003, p. §2).

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)].

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