I have now explained why I deny that the causal exclusion problem puts pressure on us to reject (Irreducibility). Along the way, I have noted a couple of desiderata that I believe any acceptable nonreductive account of mental causation should satisfy: it should reject Kim’s causal inheritance principle in an acceptable way, and it should illuminate how it is that nonreductive physicalists are able to avoid positing the sorts of coincidences that reductionists are saddled with. In the present chapter I hope to explain why we should not reject (No Overdetermination) in response to the causal exclusion problem, and to begin to set out my own positive account of mental causation.
Now, some nonreductive accounts of mental causation are explicitly put in terms of overdetermination. However, it is not always clear that those authors who adopt this language understand overdetermination as I will be doing so here. As a rough first gloss, I will say that a view rejects (Competition) if it grounds the causal efficacy of the mental in the same thing in which it grounds the causal efficacy of the physical, while it rejects (No Overdetermination) if it grounds the causal efficacy of the mental in something different. Slightly less roughly, I will say that a view rejects (Competition) if it takes the causal efficacy of a given mental property instantiation to be guaranteed by the causal efficacy of the physical property instantiation that realizes it together with facts about the nature of the realization relation, while I will say that a view rejects (No Overdetermination) if it holds that further facts must be enlisted to guarantee the causal efficacy of the mental.
I think that each of these characterizations is helpful up to a point, but I suspect things will be clearest if we simply consider different views. There are certain accounts of mental causation that intuitively seem to involve a form of causal overdetermination – regardless of whether they use overdeterminationist language are not – while there are other accounts that do not. The view of mental causation I will be defending does not. Whatever other drawbacks it may have, no one will reasonably think it involves a form of causal overdetermination. Before we get to the account I am defending, though, let me try to differentiate it from other sorts of nonreductive accounts by explaining why I reject overdeterminationist views.
I will take as my primary case of an overdeterminationist view Stephen Yablo’s account of mental causation, at least insofar as it relies on the notion of proportionality.252 This choice of targets is somewhat paradoxical, but, I think ultimately justifiable. To see how Yablo’s account works, consider the following case.
8.1.1 GILMORE’S PAIN
Gilmore is in agony. The toothache he has been suffering now for days has gotten to be so severe that he has started to sob. Suppose that firing C-fibers (PH) is the physical property whose instantiation realizes Gilmore’s pain. Then letting ‘M’ stand for the proposition that Gilmore is in pain, ‘PH’ for the proposition that his C-fibers are firing, and ‘S’ for the proposition that he sobs, the following counterfactual might be true.
(Sob): (M & ~PH) > S.
That is, it might be true that if Gilmore had been in pain without being in PH, he still would have sobbed.
To see one way this could be true, suppose that pain is a natural and multiply realized property, with some pains being realized by PH instantiations and the rest being realized by PM instantiations. Next, suppose that the closest world w where Gilmore is in pain but not in PH – that is, the closest world where the antecedent of (Sob) is true – is a world where Gilmore’s pain is instead realized by a PM instantiation. Finally, suppose that it is a physical law that PM instantiations causally necessitate sobbing, and that this law obtains at w just as it does at Gilmore’s world. Given this setup, the consequent of (Sob) will be true w. But then, on the standard analysis of counterfactuals (Sob) will be true at Gilmore’s world.
A number of philosophers believe that counterfactuals relevantly like (Sob) are of tremendous importance in solving the causal exclusion problem.253 Here though I want to focus on the role such counterfactuals play in Yablo’s extremely influential account of mental causation. In discussing Yablo’s view, I hope to establish three things. First, I want to show that Yablo’s specific account of mental causation is mistaken. Second, I want to show that the problem lies not in the details of Yablo’s account but rather in his broader orientation to the causal exclusion problem. Any philosopher who shares this broader orientation – regardless of what sort of causal significance she assigns to counterfactuals like (Sob) – will inherit Yablo’s problem. And third, I will be offering a positive proposal about the nature of the realization relation in light of the problem I pose to Yablo.
It is possible to divide Yablo’s account of mental causation into two components. First, he argues that the realization relation that obtains between mental and physical phenomena is identical (or at least very similar) to the determination relation that obtains between determinables and their determinates. On Yablo’s view, the sense in which being scarlet and being crimson are different ways of being red is importantly like the sense in which instantiating PH and instantiating PM are different ways of being pained. Now, if determinables generally do not compete with their determinates for causal influence, as Yablo claims, then this move by itself promises to go some way toward dissolving the causal exclusion problem.254
I am broadly sympathetic with Yablo here. I believe that the realization relation is importantly like the determination relation at least in certain respects. For the purposes of the present argument, I am willing to grant Yablo that realization just is determination in the present sense. The target of my objection will instead be the second component of Yablo’s account. According to Yablo, causes are generally proportional to their effects, meaning (inter alia) that causes do not corporate detail which is irrelevant with respect to bringing their effects about. This thought is meant to be capture with the following proportionality principle
(PP): A state D incorporates detail which is irrelevant with respect to an effect E, and so does not cause E, if there is some state C such that C is a determinable of D and the following counterfactual is true: (C & ~D) > E.
To see (PP) in action, consider Yablo’s example of Sophie the trained pigeon who pecks whenever she sees red.255 One day Sophie is presented with a scarlet triangle; scarlet being a shade of red, Sophie pecks. Now, is the triangle’s being scarlet properly regarded as causing Sophie’s pecking? No it is not, according to (PP). For being red is a determinable of being scarlet, and had the triangle been red without being scarlet – for instance, had it been crimson instead – Sophie still would have pecked. The intuition one is meant to have here is that it is the triangle’s being red, and not its being scarlet per se, which causes Sophie’s pecking. (PP) helps capture this sort of intuition.256
In granting Yablo that the realization relation just is the determination relation, I have in effect ensured that (Sob) is the sort of counterfactual relevant to (PP). What (PP) tells us about the Gilmore case is that if (Sob) is true then Gilmore’s PH instantiation incorporates detail that is irrelevant with respect to his sobbing, and so is not properly regarded as causing the sobbing. This opens the door to the possibility that it is Gilmore’s pain that causes his sobbing, just as in the Sophie case it is the triangle’s being red and not its being scarlet that causes the pecking. The intuitive idea here is that what the truth of (Sob) shows is that the crucial thing vis-à-vis Gilmore’s sobbing is his pain itself rather than the particular way it happens to be physically realized. After all, the sobbing still would have occurred even if pain were realized in some other physical way – for instance, by a PM instantiation.
When counterfactuals like (Sob) are false, on the other hand, Yablo’s account says that it will be the underlying physical property instantiation, rather than the mental property instantiation it realizes, that causes the effect in question. So, for instance, imagine that there is a PH-detector pointed at Gilmore while he undergoes his pain, and let ‘B ’ be the (true) proposition that the detector beeps, registering the presence of a PH instantiation. Then the following counterfactual will be false.
(Beep): (M & ~ PH) > B.
Had Gilmore’s pain had been realized by anything other than a PH instantiation – for instance, had it had been realized by a PM instantiation instead – the PH-detector would not have beeped. According to Yablo’s account, what the falsity of (Beep) shows is that it is Gilmore’s PH instantiation and not his pain which causes the beeping. In this case at least, the amount of detail that the PH instantiation incorporates is just right with respect to the effect in question.257
Summarizing then, on Yablo’s account the truth values of counterfactuals like (Sob) and (Beep) are crucial to our commonsense and scientific attributions of mental causation. When such counterfactuals are true, as in the case involving (Sob), such attributions will be correct: it really is Gilmore’s pain that causes him to sob. When such counterfactuals are false, as in the case involving (Beep), such attributions will be incorrect: it isn’t Gilmore’s pain but his PH instantiation which causes the PH-detector to beep. His PH instantiation causally excludes his pain with respect to this particular effect.
8.1.3 YABLO AS AN OVERDETERMINATIONIST
On Yablo’s view, if (Sob) is true then it is Gilmore’s pain and not his PH instantiation that causes him to sob. And yet, he emphasizes, the PH instantiation still has some sort of positive causal status – it is still causally sufficient for the sobbing.258 Now, however the details of his view go here exactly, Yablo must understand causal sufficiency in a fairly robust sense. In particular, causal sufficiency must be robust enough to underwrite the causal closure of the physical realm, since Yablo’s account is meant to be compatible with the truth of physicalism. It is because Yablo’s robust causal notions split apart in this way that I categorize him as a kind of overdeterminationist. That Gilmore’s pain causes his sobbing is grounded in one thing – namely, the pain’s being proportional to the sobbing. That Gilmore’s PH instantiation is causally sufficient for his sobbing is grounded in something else – it cannot be grounded in proportionality, since the PH instantiation isn’t proportional to the sobbing.259
Already I think we have the makings of a problem for Yablo’s view here. Again, it is absolutely crucial according to Yablo that mental events be proportional to their purported effects. The vital role of proportionality is perhaps made clearest by Yablo’s suggestion that a proportional mental cause is required if a bit of behavior is to qualify as an intentional action.260 If this suggestion is correct, then a world in which all mental events are disproportional to subsequent effects – in the way that Gilmore’s pain is disproportional to the beeping of the PH-detector – will be a world in which there are no intentional actions. Maybe some hands go up in a world where all counterfactual relevantly like (Sob) and (Beep) are false, but none of those hands are raised.261
But, we might wonder, is there any causal relation – be it a relation of causal sufficiency, causal relevance, causal influence, causation itself, or whatever262 – such that (i) it is absolutely crucial to mental causation that the relation in question obtains between mental events and their purported effects, so that in the absence of that relation obtaining there can be no intentional action; and yet (ii) it is not crucial from the standpoint of physicalism that the relation obtain between physical events, so that even if this relation often fails to obtain between physical events (especially those events that realize mental events), the physical realm could still be causally closed in the way that physicalism requires. I find it wildly implausible that there could be any causal relation satisfying both (i) and (ii). If proportionality is such a precious thing that there could be no robust mental causation without it – and so no intentional action, for instance – then surely it is something that a properly formulated causal closure principle ought to require between physical events as well. On the other hand, if proportionality between physical events is something that a properly formulated causal closure principle will not require, then surely it is not something that mental causation requires either. It is this latter option I will be exploring; I believe that there can be robust mental causation in the absence of proportional mental causes.