Sometimes philosophers who accept a view roughly like the Shoemakeresque view seem to hold that the key to solving the causal exclusion problem is to accept a kind of token identity thesis. Not the Davidsonian token identity thesis, according to which mental events are identical to physical events. Davidsonian events are too coarse-grained. Rather, the key is to accept a causal power token identity thesis, according to which the token causal power that is exercised in an instance of mental causation is identical to a token causal power that is exercised in a related bout of physical causation. Token causal powers are as fine-grained as our finest causal distinctions, and so a token identity thesis of this sort might just do the trick, the thought seems to go. The account of mental causation I now want to give fits well with this view. First, though, let me say a bit about what it is for a causal power token to be exercised.
9.2.1 THE EXERCISE OF CAUSAL POWERS
Regardless of whether or not one accepts the Shoemakeresque view, one will want to say that causal power tokens are sometimes exercised – recall the candlestick and revolver example from above. But now, how should we understand this talk of causal powers being exercised on the Shoemakeresque view? A natural thought would be to understand the exercise of causal power tokens in terms of the obtaining of causal relations between natural property instantiations. But, it is unclear that such an understanding is consistent with the reductive causal structuralism we are assuming. Do we then need to treat the exercise of token causal powers as a new primitive notion?
No we do not. Token causal powers are property instantiations, or events, and events are the sorts of things that generally can enter into causal relations. In light of this, let’s say that a token causal power is exercised just in case it causes some effect.300 Just as causal powers need not be understood as entities of some drastically new sort, the exercise of causal power tokens need not be understood as anything drastically new. It is just a matter of certain events (causal power tokens) causing effects.
Understanding the exercise of causal powers in these terms involves attributing causal efficacy to powers themselves.301 So for instance, it involves saying that a sleeping pill’s dormitive power causes the person taking it to fall asleep. Obviously, some philosophers will find this objectionable. For some, this is because the connection between dormitivity and falling asleep is necessary, while causal relations are often thought to be contingent.302 We parted company with these philosophers long ago, though – back when we began entertaining causal structuralism in the first place (of either the reductive or nonreductive variety). If the relation between natural properties and their causal profiles is necessary, then the sort of necessary connection that obtains here between dormitivity and sleeping will be characteristic of all causal relations.
In taking causal powers themselves to enter into causal relations, then, it does not seem we are burdening the Shoemakeresque view with any further implausibility, that is, any implausibility over and above that which it already faces.303
9.2.2 MENTAL CAUSATION AND THE PART/WHOLE CAUSATION THESIS
After just one more definition, we will finally get to the account of mental causation. Let’s say that a token causal power of a natural property instantiation is exercised just in case (i) that token causal power is a part of the natural property instantiation in question, and (ii) that token causal power causes some effect. Generally when philosophers speak of a token causal power being exercised, what they mean is that a token power of some specific natural property instantiation is exercised. The present definition is meant to capture such talk.
Given this setup, consider the following substantive metaphysical thesis.
The Part/Whole Causation Thesis: A natural property instantiation causes some effect just in case some of its token causal powers are exercised in bringing about that effect. That is, just in case some of its token causal powers cause that effect. That is, just in case some of its parts cause that effect.
According to this thesis, when a natural property instantiation causes an effect it is relevantly like the Battle of the Bulge causing the Germans to retreat to the Siegfried Line. A natural property instantiation’s parts, certain causal power tokens, cause the effect in question, just as the Battle of the Bulge’s parts, certain small-scale skirmishes, cause the German retreat. Causation is like touching, according to the thesis. If the top half of a baseball touches a bat, the baseball itself (a whole) touches that bat. Again, the part/whole causation thesis is not a definition but a substantive metaphysical claim that can be coherently denied. Below we will consider objections to the thesis. For now, though, let’s provisionally grant its truth and see what follows.
Given the part/whole causation thesis, it follows that if some causal power token is a part of two non-identical natural property instantiations, both of those natural property instantiations will cause any effect that is caused by the causal power token itself. Consider a token of the causal power type b which is a part of both a pain instantiation and a PH instantiation. Suppose that this b-token causes some effect. Then given the whole/part causation thesis, it follows that this effect is caused by both the pain and the PH instantiation. Intuitively, though, we no more have causal overdetermination in this case than we have causal overdetermination in the case of the Battle of the Bulge, where both the battle itself and the many small-scale skirmishes that compose it cause the German retreat.
Philosophers discussing the causal exclusion problem often make a point of emphasizing that mental events are not partial causes which, acting in concert with physical events, bring about their effects.304 This is correct, according to the present account of mental causation, but only thanks to the inclusion of the italicized bit. Every effect has as a full cause a physical event, we can grant. But mental events are parts of physical events, and so we can still think of mental events as partial causes of their effects without positing overdetermination.
Imagine a PH instantiation that realizes a pain, and suppose that all of the causal power tokens that compose the PH instantiation conspire together to cause some effect in such a way that the PH instantiation qualifies as the full cause of that effect. Then, the pain that the PH instantiation realizes is a partial cause of that effect while the other partial cause is the instantiation of (e & f & g & h). This conjunctive property is no natural property, let’s assume following Shoemaker, but rather a motley conjunction of causal powers. Thus, the other partial cause of the effect in this case is not some physical event, and much less a mental event, but rather just a composite event made up of a motley collection of causal power tokens. Again though, this is completely compatible with the full cause of the effect being a physical event.
Think back to the match striking example used in the introduction to this chapter. We can regard the striking of a dry match as a composite event with two parts, the match’s being struck (one property instantiation) and its being dry (another property instantiation). If the striking of the dry match causes it to light, then, intuitively, the striking of the match is a partial cause of this effect, a cause that acts in concert with the match’s being dry. And intuitively, at least, this involves no recognizable form of causal overdetermination.
According to the present account of mental causation, the relation between mental events and the physical events that realize them is at least somewhat like the relation between the striking of a match and the striking of a dry match. The striking of a match will cause that match to light only if it is dry. At least somewhat similarly, according to the Shoemakeresque view, a causal token of a pain instantiation – a b-token, say – will be exercised only if it is coinstantiated with certain other causal power types. For instance, only if it is coinstantiated with tokens of the causal power types e-h, or tokens of the causal power types e, i, j, and k, or etc. That is, only if the pain is physically realized in some way or other. If physicalism is true then every pain will be physically realized in some way or other, and so no causal power token of pain will be exercised in the absence of this sort of coinstantiation. In this way, at least, the relation between pain and its physical realizers is like the relation between the striking of a match and the striking of a dry match.
9.2.3 CATEGORIZING THIS ACCOUNT
This account of mental causation, which is inspired in no small part by the views of Yablo and Shoemaker (once they have been rightfully purged of their proportionality elements), is extremely promising, it seems to me. If it works, it effectively reduces the problem of nonreductive, physicalistic mental causation to something that intuitively seems far less problematic, part/whole causation. Back in Chapter 8, I said that a nonreductive, physicalistic account of mental causation counts as rejecting (Competition) rather than (No Overdetermination) if it grounds the causal efficacy of the mental in the same thing in which it grounds the causal efficacy of the physical. The present account is meant to capture that thought. It claims that the same causally efficacious causal power tokens that are parts of mental events are also parts of the physical events that realize those mental events. Even aside from my way of trying to characterize the divide between rejecting (Competition) and (No Overdetermination), though, it seems to me that intuitively, the present account should be viewed as a rejection of (Competition). Intuitively, it’s not that mental and physical phenomena causally compete but “tie,” according to the present view. (This is how we should think of overdeterminationist views, it seems to me.) Rather, it’s that there is no causal competition in the first place.
9.2.4 WATERED DOWN PROPORTIONALITY
It may be helpful to incorporate a greatly watered down conception of proportionality into the present account. While Yablo takes proportionality to figure in the account of causation itself (as does Shoemaker, apparently), it strikes me as far more plausible to think of proportionality as part of the account of how, given multiple events that all causally contribute to some effect, we pick out some event as the cause of that effect.305 Suppose that I light a match in the middle of a desert, where everything is bone dry for miles and miles. Given the context, it would be odd to single out the match’s being dry as the cause of its lighting. By extension, it might also be odd to single out the match’s being struck and dry as the cause of its lighting. A far more natural selection as the cause would be just the match’s being struck. Similarly perhaps, it may be that when a mental event, rather than the physical event that realizes it, is proportional to some effect, it will be most natural to call that mental event the cause of that effect.
I assume here that nothing of real metaphysical importance turns on which event we select as the cause of an effect.306 How we pick out one event rather than another as the cause of an effect seems to be a largely pragmatic affair, reflecting our own explanatory interests as much as anything. If this is right, then from the standpoint of what really matters regarding mental causation, it would appear to be of no real consequence at all whether or not mental events should be singled out as the cause of their purported effects. If it were to turn out that mental events are causally related to their purported effects “merely” in the way that the desert match’s dryness is causally related to its lighting, it seems to me we should regard that as the complete vindication of mental causation. If mental events are not the causes of their effects, it would be nowhere near the end of the world Fodor describes.
Still, it will be useful to introduce watered down proportionality into the present account, if just to use it in precisely the opposite way that Yablo does. The idea is this. To the extent that the present account of mental causation yields certain results that initially appear somewhat counterintuitive or otherwise problematic, perhaps we can explain those appearances away as the result of mere, metaphysically uninteresting, watered down proportionality considerations. So for instance, perhaps watered down proportionality considerations show that for some physical effect, the cause of that effect is a mental event rather than the physical event which realizes it. Would this undermine (Closure)? No, because all we are talking about here is what gets to be called the cause of the physical effect in question, not anything more metaphysically interesting. Even if it were to turn out that physical events are never best singled out as the causes of physical effects, no physicalist should regard this as the end of her world.307
9.2.5 OBJECTIONS TO THE PART/WHOLE CAUSATION THESIS
I now want to consider a pair of objections to the part/whole causation thesis which is at the center of the present account of mental causation. First, consider an objection derived from Trenton Merricks’ Overdetermination Argument against the existence of ordinary material objects, like baseballs.308 Imagining a case in which an (alleged) baseball causes an (alleged) window to shatter, Merricks sets out his argument as follows.
(P1): The baseball – if it exists – is causally irrelevant to whether its constituent atoms, acting in concert, cause the shattering of the window.
(P2): The shattering of the window is caused by those atoms acting in concert.
(P3): The shattering of the window is not overdetermined.
(C): If the baseball exists, it does not cause the shattering of the window.
Merricks takes this argument to generalize to all purported effects of alleged (non-living) macrophysical objects. But, if such objects do not cause any effects, then plausibly they do not really exist. Merricks embraces this eliminativist conclusion, denying the existence of baseballs and the rest.
Merricks’ original argument is restricted to composite objects, but it is not difficult to imagine how an analogous argument applying to composite events might go.309 Given the nature of Merricks’ argument, it is fair for me to pick any composite event I please to play the role that Merricks’ baseball plays for him. So I pick the striking of a dry match. Given this choice, here is the analog to Merricks’ argument.
(P1’): The match’s being struck and dry – if it (the composite event) exists – is causally irrelevant to whether its constituent events, the match’s being struck and its being dry, acting in concert, cause the match to light.
(P2’): The match’s lighting is caused by its being struck and its being dry, acting in concert.
(P3’): The lighting of the match is not overdetermined.
In short, the idea is that given that the match’s being struck together with its being dry fully account for its lighting, there is no room for its being struck and dry to do any causal work. I find it difficult to work myself up into a frame of mind from which this version of the argument seems compelling. Surely, I want to say, if a match’s being struck and dry is incapable of causing it to light, then this is a bad way of trying to light it: making sure the match is dry, and then striking it. That is, the truth of (C’) seems to me to entail the negation of (P2’). The only real question is whether to reject (P1) or deny the argument’s validity. Given how Merricks defines “causal irrelevancy” in his original argument, the proper choice is to deny validity.310 The causal efficacy of the match’s being struck and dry seems about as relevant as anything possibly could be to the causal efficacy of the match’s being struck, acting in concert with the background condition of the match’s being dry. But given Merricks’ definition, we must regard this as a form of non-causal relevancy.311
Even aside from the details of my objection to Merricks’ argument (or at least its analog for composite events), there is a broader and more important point to make here. Presently, there are several loosely related causal exclusion problems floating around in philosophy: one that applies to irreducible mental phenomena, another that applies to composite material objects, and yet others that apply to various other entities. Much of the appeal of the present account of mental causation is that it assimilates mental/physical causation to causation by distinct wholes which have parts in common. At least naively, part/whole causation does not seem especially problematic, and so this assimilation seems to constitute genuine progress in accounting for mental causation. Given this context, part of the threat of Merricks’ argument is that it might seem to show that no real progress has been made, since wholes face a causal problem of their own. What’s more, it might seem to show this regardless of whether or not the argument is sound. Suppose there is some flaw with Merricks’ argument. Even so, if we now must make further moves to diagnose that flaw, then how has the present account of mental causation advanced the discussion in any way? Why not just make those further moves and leave the present account of mental causation completely to the side?
What this line of questioning overlooks is that, despite bearing a kind of family resemblance to one another, the two causal problems in question are importantly different. Solutions available for one causal problem may be unavailable for another. Consider for instance the view that composition is identity, defended in a strong form by Donald Baxter and in a more modest form by David Lewis.312 If composition is identity, then presumably there is no causal competition between parts and wholes, just as if mental properties are identical to physical properties, there is no causal competition between them. Notice, though, that the view that composition is identity would not in any way undermine the nonreductive status of the present account of mental causation. If composition is identity then mental events are identical to the causal power tokens that compose them, while physical events are identical to the distinct causal power tokens that compose them.313 Given this distinctness, the irreducibility of the mental to the physical is preserved.
Moreover, the considerations that speak for and against the view that composition is identity are generally quite different from the considerations that speak for and against the view that mental properties are identical to physical properties. Thus, there need not be even the slightest tension in holding on the one hand that wholes are identical to their parts while holding on the other that mental properties and events are distinct from physical properties and events. There is a loose connection between the different causal exclusion problems, but that is all that there is.
My aim here is not to defend the view that composition is identity, or any other similarly specific view. Rather, it is to observe that the assimilation of mental/physical causation to causation by distinct wholes having parts in common can and does constitute genuine progress in solving the causal exclusion problem facing irreducible mental phenomena, regardless of whether some philosophers have raised supposed causal problems for wholes. If the account of mental causation presently under consideration were able to show that nonreductive physicalistic mental causation is no worse off than is causation by a match’s being struck and dry, that would constitute remarkable philosophical progress.
Let’s now turn to the second objection to the part/whole causation thesis. Not all parts of whole are related to one another in the way that the striking of a match is related to the match’s being dry. Consider a skirmish occurring within the Battle of the Bulge that causes the death of a soldier. Suppose that even if the skirmish had not been part of a larger battle, the soldier still would have died, provided that the skirmish occurred just as it did. Then unlike the match striking case, the rest of the Battle of the Bulge (the battle’s other parts) does not seem to constitute a background condition which the skirmish was operating against in causing the soldier’s death. Do we nevertheless want to say that the Battle of the Bulge itself causes the soldier’s death?
It seems that we should. If we deny that the battle causes this soldier’s death, then presumably we will also need to deny that the battle causes any soldier’s death. So the battle causes no deaths at all. Generalizing, presumably no battle causes any deaths. Generalizing further, presumably no war causes any deaths. But if wars do not cause deaths, then it is hard to see how they could cause any effects at all. If wars cause no effects, though, then presumably they do not exist. This conclusion is too good to be true. The present objection to the part/whole causation thesis appears to end up being not much less radical than the objection derived from Merricks considered above.
The far more natural way to handle the case here, it seems to me, is to hold that the battle itself does cause the soldier’s death, but allow that it might be odd to single out the battle as opposed to the skirmish as the cause of the death, given the proportionality considerations in play – that is, given that the death would have occurred so long as the skirmish occurred, even if it were not part of a larger battle. This result would be perfectly consistent with the part/whole causation thesis, which says nothing about when parts as opposed to wholes (or vice versa) will be most deserving of the label of the cause for some effect. We will return to these issues in the section that follows.