Call any true generalization that is like (3) in that it both ranges over physically dissimilar events and does not express an analytic truth a C-generalization (for coincidence).233 The more true psychological C-generalizations we empirically discover, the less plausible realizer-state functionalism becomes.
7.2.1 THE IBE ARGUMENT
Suppose that in addition to confirming the truth of (3), we discover that in certain specified circumstances both human pains and Martian pains cause bloodshot; in other circumstances, they both cause ingrown toenails; and in yet in other circumstances, they both cause failing kidneys. To introduce generalizations that add a new dimension to the discussion, suppose that after we discover Martians we further discover Venusians, Jupiterians, Mercurians, etc. In each of these species, a different physical property occupies pain’s causal role. And yet in each of these cases, the newly discovered pains cause hair loss, bloodshot eyes, ingrown toenails, failing kidneys, etc.234
This sort of confluence of causal powers across pains is something that would cry out for explanation. Again, the hypothesis that pain is a natural and multiply realizable mental property would straightforwardly explain why all the pains in question behave alike: it would be just a special case of the general rule that different instantiations of a single natural property behave alike. The realizer-state functionalist, by contrast, has no good explanation. It seems that she would need to treat such findings as just coincidence after coincidence, akin in each case to the discovery that both emeralds and alligators are green. Gradually, this explanatory strategy becomes untenable. It becomes too implausible to think we keep discovering just coincidence after coincidence. The better (best) explanation is that pain is a natural and multiply realizable property. But reductionists deny that there are any such properties. Thus, according to the IBE argument, we ought to reject reductionism.
It’s not that there is any strict threshold, a magic number n such that once we discover n many true psychological C-generalizations, realizer-state functionalism will have been disproved. Rather, it’s that realizer-state functionalism gives us absolutely no reason to expect to find true psychological C-generalizations, while alternative metaphysics of mind do. As is generally the case in abductive inference, the theory that predicts the results we are imagining to obtain provides a better explanation for those results than does a theory that, though not inconsistent with the results, makes them seem surprising. Each true psychological C-generalization we discover is surprising from the standpoint of realizer-state functionalism, and so each such generalization we discover is a further bit of evidence in the accumulating abductive case against the view.
This is a thoroughly empirical argument (or rather, argument scheme at this point, since we have not yet considered C-generalizations that are actually true). There are certain areas of metaphysics in which empirical checks on our judgments are difficult if not impossible to come by. Thankfully, the area of which properties are natural is not one of them. It is, in fact, a paradigm case of an area of metaphysics that is amenable to empirical checks. After all, the only reason that realizer-state functionalists (or anyone else for that matter) thinks that various physical properties are natural is because of the empirical success of physics. By taking on certain commitments regarding what sorts of properties are natural and what sorts are not, realizer-state functionalists subject their view to empirical disconfirmation in just the same way that the metaphysical thesis that being jade is a natural property has been empirically disconfirmed.
Any nonreductive physicalist who posits natural and multiply realizable mental properties will need to accept (Irreducibility), and so any such philosopher will need to reject either (No Overdetermination) or (Competition) or both. But what if it turns out that these theses cannot be rejected in an intuitively satisfying way? In light of the present argument, a case can be made that we nevertheless ought to reject (at least) one of them. For one of the absolutely central tasks for an account of natural properties is to render our scientific successes unmiraculous. Any account that cannot do this must be rejected, whatever its other virtues. If we think of empirical psychology as devoted in no small part to discovering true psychological C-generalizations, then realizer-state functionalism’s metaphysics renders empirical psychology’s successes on this front miraculous. We can read something like this thought into the following passage from Fodor.
Science postulates the kinds [i.e., natural properties] it needs in order to formulate the most powerful generalizations that its evidence will support. If you want to attack the kinds, you have to attack the generalizations. If you want to attack the generalizations, you have to attack the evidence that confirms them. If you want to attack the evidence that confirms them, you have to show that the predictions that the generalizations entail don’t come out true. If you want to show that the predictions that the generalizations entail don’t come out true, you have actually to do the science. Merely complaining that the generalizations that the evidence support imply a philosophically inconvenient taxonomy of kinds cuts no ice at all. So far, anyhow, when the guys in the laboratories actually do the science, they keep finding that mental kinds are typically MR [multiply realized], but that the predictions that intentional psychology entails are, all the same, quite frequently confirmed.235 I don’t agree with everything Fodor says here. As I’ve already explained, I take realizer-state functionalism (and reductionist views generally) to be consistent with the predictions Fodor mentions – that is, predictions regarding the truth of psychological C-generalizations. In my view, the real issue is that if realizer-state functionalism gives us no good reason to expect those predictions to come out true, and so we would need to regard it as a matter of luck when they do come out true. This disagreement with Fodor is a quibble though. If the realizer-state functionalist’s position is to be at all plausible, then she needs to “do the science” and show that the predictions in question turn out to be (at least often) wrong.
To connect this back to the point about (No Overdetermination) and (Competition), suppose again that it turns out that there are no intuitively satisfying ways to reject either of these theses. If the choice is then between rejecting one of them in an intuitively unsatisfying way and adopting a metaphysics that renders our scientific success miraculous, then a strong naturalistic case can be made that we ought to go with the former option. Thankfully, I do not think this is a dilemma we actually face. I believe it is possible to reject (Competition) in an intuitively acceptable way. But if it weren’t, I’m inclined to think we should just be happy that this area of metaphysics, unlike others, provides us with external, empirical checks on the correctness of our intuitive views.
This line of argument touches on a sentiment one finds both in Fodor’s writings and in the writings of other philosophers who argue against reductionism along lines broadly similar to the ones I’m pursuing here. It is that reductionists – or at least those reductionists who, like realizer-state functionalists, are driven to their position by metaphysical considerations such as those pertaining to causal exclusion – are not sufficiently naturalistic.236 Less paradoxically, we might instead say that these philosophers’ naturalism is dominated too much by an appreciation of physics to the exclusion of special sciences like psychology.
The IBE argument just presented is heavily inspired by another thoroughly empirical argument against reductionism, Fodor’s argument from the existence of special science laws.237 Perhaps, though, the IBE argument manages to avoid some of the more controversial premises of Fodor’s original argument; or, failing this, perhaps it manages to highlight the argument’s real crux in a useful way. Fodor’s argument turns on the thesis that there are certain empirically discovered special science laws – more specifically, laws in the form of C-generalizations – for which reductionist views are unable to account. That is, reductionists are unable to treat these laws as laws. In defending this claim Fodor appeals to several highly disputed (though perhaps ultimately defensible) theses about laws. This includes theses about how laws are individuated, whether there are any special science laws at all, and (closely connected with this last point) whether there are ceteris paribus laws.
Instead of directly getting caught up in these issues, I find it more helpful to focus on the question of whether true generalizations relevantly like (3) should be regarded as coincidences in the sense described. If we empirically discover that human, Martian, Venusian, and Jupiterian pains all cause hair loss, and then we inductively infer from this that Mercurian pains cause hair loss too, would this inference be justifiable? If it proved to be correct, should we regard this as mere luck?
Perhaps the IBE argument can be made without signing on to every controversial claim Fodor advances regarding laws. Suppose for instance that a property can qualify as natural even if it figures in no natural laws. If so this would allow us to remain neutral on whether pain figures in any natural laws even as we use the IBE argument to attempt to establish that pain is a natural (and multiply realizable) property. This in turn would allow us to remain neutral on the theses Fodor advances regarding laws. In that case, those philosophers who object to Fodor because they deny that there are any special science and/or ceteris paribus laws need not find anything objectionable in the IBE argument.238 In effect, such philosophers could be broken off from those reductionists who oppose Fodor on grounds that will also require them to oppose the IBE argument.
Perhaps, though, the link between natural properties and natural laws cannot be cut in this way. If not, then presumably the IBE argument’s establishing that pain is a natural (and multiply realizable) property would entail that various ceteris paribus generalizations in which pain figures, like (3), qualify as psychological laws. If so, it would then seem that one of the more power arguments to be made against those philosophers who deny that there are any special science and/or ceteris paribus laws is that they are forced to regard those true C-generalizations we discover as coincidences in the sense described. That is, the views of these philosophers, just as much as the views of realizer-state functionalists, would then be susceptible to the sort of IBE argument I have set out.
7.2.3 EXTENDING THE ARGUMENT
While I have been focusing on realizer-state functionalism, the IBE argument obviously generalizes to the other reductionist views that we considered in Chapter 6, since both the disjunction identity theory and eliminativist functionalism deny the existence of natural and multiply realizable mental properties. I do not know of a knockdown way of establishing that the IBE argument will apply to any conceivable form of reductionism, since I do not know of a knockdown way of establishing that any view that is reductionistic must ipso facto deny the existence of natural and multiply realizable mental properties. However, in advance of seeing a worked out view that is both intuitively reductionistic and yet fully accepting of such properties, I’m inclined to think that it can’t be done.239