The topic of mental causation in contemporary philosophy of mind is a vexed one, constrained by only one rule: avoid epiphenomenalism. There is a deep sense that there simply has to be mental causation of some kind – our psychological/mental states – beliefs, desires, intentions – must, in some way, have some causal influence over or on our behaviour. Whatever else may or may not be the case, this is something we have to have. This is the data we have to explain.
There are, generally, two broad ways to approach the issue of mental causation (MC): either the mind/body are two distinct substances (substance dualism, SD) or they are not (let’s call this broad physicalism, BP – and we’ll assume that an account of BP aims to be non-reductive). This lets us divide up the problems of MC a bit more easily:
On SD, if the mind and body are two distinct substances, one material and one immaterial, the issue becomes just how to explain, describe and define the causal relation between the mind and body. Simply put, what is the nature of the causal relation here? The objections here are well known: how could an immaterial substance be in any kind of causal relation with a material substance? It just seems odd that such a relation exists – and if the mind is independent from the brain, as SD claims, then what do we make of the cases where, say, a blow to the head (or the aftereffects of brain trauma, such as agnosia) disrupts consciousness or conscious processes? The opposite would seem like the natural conclusion – if the mind truly is independent from the brain, then consciousness should continue uninterrupted by any kind of physical disturbance.
William Hasker identifies a related issue in his book ‘The Emergent Self’:
‘Phillip Quinn doubts this: “I’d be willing to bet that we will learn from neuroscience…that thus processing of visual information goes on in the brain. And if a Cartesian mind requires as input processed rather than unprocessed visual information in order to perform such tasks as identifying faces and reading facial expressions, it will come as no surprise that it can’t perform that it can’t perform such tasks if its damaged brain can’t provide it with the processed visual information it requires as inputs.”
The problem with this lies in the strong probability that, as neuroscience progresses, more and more of our “advanced” mental processes will be found to be associated with, and dependent upon, specific brain processes. When that happens, Quinn’s strategy would lead us to a view of the conscious mind as essentially a passive spectator, enjoying awareness but contributing little or nothing of its own to those results.’ (p. 155)
Epiphenomenalism by any other name…
What of our other position, Broad Physicalism? Here the issue takes a similar form: how to account mental causation with only material substance (only the physical) without lapsing into epiphenomenalism. Immediately an objection jumps out at us: if, as one would think is necessary for BP, physical explanation is necessary and sufficient, what role is there for the mental? It seems as though epiphenomenalism is waiting to pounce.
There’s a few possible solutions here. Supervenient causation is one of those solutions, but it’s difficult to find an acceptable version of it that doesn’t end up becoming reductive. Type-identity theories have more or less gone by the wayside, replaced with a more hopeful alternative, token-identity theories, where mental-event tokens are identified with physical-event tokens, which avoids the problem of multiple realization that plagued type-identity theories – and if. Here the problem becomes one of identification of events, and Donald Davidson supplied an account: an event is identical to another event if their causes and effects are identical. This ties in to his theory of anamolous monism: mental states are not governed by any strict laws, and thus cannot be reduced to physical states or given a pure physical explanation, since physical explanation involves strict laws. This position recognizes that mental events are physical events without reducing them to only physical events.
The payoff here is that if mental events can be identified with brain events, then it is easy to see how there is mental causation. Hasker notes a difficulty here, though, with Davidson’s identity criterion:
‘Put briefly, the theory is circular: causal relations are identified by the events they relate, and events are identified by the causal relations in which they stand. Clearly, one or the other has to be identified in some other way, so as to enable us to break into this closed circle. And since there seems to be no prospect of identifying causal relations except as relations between events, it seems that it will have to be the events themselves which are characterized in some other way.’ (‘The Emergent Self’, p. 38)
Jaegwon Kim notes another difficulty with Davidson’s theory of anamolous monism:
‘Davidson’s anamolous monism fails to do full justice to psychophysical causation in which the mental qua mental has any real role to play. Consider Davidson’s account: whether or not a given event has a mental description seems irrelevant to what causal relations it enters to. Its causal powers are wholly determined by the physical description or characteristic that holds for it; for it is under its physical description that it may be susbsumed under a causal law.’
Kim proposes a different theory of identification: events are exemplifications by substances of properties at a time. This view is well-known and seems to be the strongest account of token-identity, but it suffers from the difficulty not of being circular but of multiplying events beyond reason. If Kim’s theory is true, then, as the well-known critique goes, no stabbing is ever a killing, since the stabbing and killing are two different properties. Simply put, Kim cannot identify events with each other because they are not identical. Brutus stabbing Cesear is not the same as Brutus killing Cesear. The payoff here, as noted by Davidson, is that Kim cannot identify brain events with mental events, which seems to be a significant weakness for a token-identity theory.
Where does this meandering leave us, then? On SD, we have the interaction problem: how do two substances, one material and the other not, interact? On BP, it seems that there is serious difficulty giving an account of mental causation that is actually an account of mental causation. My first reaction is, noting the serious difficulties with thinking of the mind/body relation in terms of causal relations, to think of the mind/body relation in non-causal terms. This is the Aristotelian position of hylomorphic dualism, which, for the sake of sanity I will leave for another day. But the takeaway, I think, is this: perhaps the mind/body relation needs to be thought of in non-causal terms.