Christopher Devlin Brown, “Exclusion Endures” forthcoming in Analysis

This is an interesting paper which, together with John Donaldson’s forthcoming “Horizontal vs Vertical”, has usefully focused my attention on the real nature of the compatibilist’s solution to the causal exclusion problem.

Brown’s claim is that the compatibilist approach, advanced by non-reductive physicalists like Karen Bennett (2003), can also be exploited by dualists, as a way to avoid the causal-closure argument for physicalism. 

The causal exclusion problem poses similar challenges to the dualist and the non-reductive physicalist. They both want to say that mental causes are distinct from physical ones.  But, given the causal closure of the physical, they want to say that mental causes’ effects have sufficient physical causes as well. The combination makes mental properties look redundant: at worst, they are epiphenomenal and so not mental causes at all; at best, their effects are systematically overdetermined, which is bizarre. 

The “compatibilist” response from the non-reductive physicalist is to accept that mental and physical causes double up as causes of their effects, but then deny that this is objectionable—on the basis that the mental and physical causes are not wholly distinct, since the former depends ontologically on the latter.  That means the problematic overdetermination counterfactual—if the mental cause had not occurred but the physical cause had, the effect would still have occurred—is only vacuously true.  The antecedent can never be satisfied, since if the mental cause is removed the physical cause goes away with it. 

This approach doesn’t seem like an option for a dualist. Dualists thinks mental and physical are ontologically distinct. That’s kind of the point.

Browne’s suggestion, however, is that the dualist can suggest a different sort of necessary connection—one that is not ontological but nomological. Say laws of nature are metaphysically necessary, and there are psychophysical laws connecting the mental and physical causes. That’s enough to make the overdetermination counterfactual vacuously true, since removing the physical cause necessarily removes the mental one too. Why think the laws of nature are necessary? Perhaps because you accept dispositional essentialism: the idea that properties have their nomological roles necessarily. Those are both controversial views, and not ones I endorse.  But they are respectable positions, so the dualist’s position against the causal closure argument has at least been strengthened. 

Can the physicalist respond? One question is about the nature of the psychophysical laws. If the relation between mental and physical properties is not ontological (not constitution, realisation, etc) presumably the law connecting them must be causal. (What else could it be?) And more specifically, the physical property has to cause the mental one. (The other direction would seem to assume what we’re here to explain.)

But. Now the picture is one of redundant causation. The physical cause produces both a physical effect and a mental cause, which also produces the physical effect.

The systematic causal detour tbrough the mental property looks just as otiose and objectionable as an autonomous mental cause would be. Making that extra causal route necessary by way of dispositional essentialism does not look like an advance, even if it does handle the counterfactuals. Consider an example: say that throwing rocks at windows breaks them in the usual way, but also (with nomological force) causes a particular phenomenal experience in the thrower, which also (and independently) breaks the windows.

The moral here, I think, is that Bennett’s vacuous counterfactual analysis is just a way of handling the formalities. The substantive insight which the compatibilist physicalist can offer is the non-distinctness of the mental and physical causes. That is what makes the existence of multiple causes harmless. In other words, the exclusion problem needs what John Donaldson calls a “vertical” solution, on which more soon.