|Philosophy of Mind
Restoring Mind-Brain Supervenience: A Proposal
Robert G. Lantin
ABSTRACT: In this paper I examine the claim that mental causation at least for cases involving the production of purposive behavior is possible only if mind/brain supervenience obtains, and suggest that in spite of all the bad press it has received in recent years, mind/brain supervenience is still the best way for a physicalist to solve the exclusion problem that plagues many accounts of mental causation. In section 3, I introduce a form of mind/brain supervenience that depends crucially on the idea that some brain state-types-namely, those involved in the production of purposive behavior-are nonlocally sensitive, where by nonlocal sensitivity I mean cases where relevant causal histories and environmental circumstances effect a difference in some of an organisms brain state-types intrinsic, causal properties. I will argue that such a mode of sensitivity of brain state-types offers the best way out of the exclusion problem for anyone convinced that mental state-types should be relationally individuated.
In what follows, I examine the claim that mental causationat least for cases involving the production of purposive behavioris possible only if mind/brain supervenience obtains, and suggest that in spite of all the bad press it has received in recent years, mind/brain supervenience still is the best way for a physicalist to solve the exclusion problem that plagues many accounts of mental causation. In section III, I introduce a form of mind/brain supervenience that depends crucially on the idea that some brain state-typesnamely, those involved in the production of purposive behaviorare nonlocally sensitive, where by nonlocal sensitivity I understand cases where relevant causal histories and environmental circumstances effect a difference in some of an organisms brain state-types intrinsic, causal properties, and argue that such a mode of sensitivity of brain state-types offers the best way out of the exclusion problem for anyone convinced that mental state-types should be relationally individuated. (1) It is important to notice from the outset that nonlocal sensitivity, as I understand it, is not equivalent to relational individuation. Indeed, I am not claiming that a change in a brain state-types relational properties effects a difference in its intrinsic, causal properties. I agree that brain state-types should be individuated nonrelationally, but introduce local and nonlocal sensitivity as modes of nonrelational individuation of brain state-types, and argue that nonlocally sensitive brain state-types make up the proper subvenient base for mental state-types. If my view is correct, strong mind/brain supervenience is restored, and the exclusion problem solved. (2) Yet, since I do not explicitly argue against the nonrelational individuation of mental state-types, I must grant the plausibility of the solipsists course of action out of the exclusion problem. Judging by the amount of controversy still surrounding the notion of narrow content, however, it seems clear to me that there is currently no consensus in the community as to what the view would look like, and so I believe the articulation of an externalist proposal is well worth the effort.
According to a large number of philosophers, mental causation refers to cases where instancings of mental properties (mental events) enter causal relations as causes and/or effects. We may thus distinguish three kinds of causal relations that fall under the heading of mental causation: (i) physical-to-mental causation (as when severe burns cause a sensation of pain); (ii) mental-to-mental causation (as when the belief that it will rain later on prompts you to wonder whether you should cancel the afternoon picnic); and (iii) mental-to-physical causation (as when the thought that time has come for your next dental exam prompts you to pick up the telephone and call your dentist to set an appointment). The present paper focuses particularly on cases of the latter kind.
Mental-to-physical causation is typically involved in the production of purposive, intentional behavior. We are all quite familiar with such cases, and seemingly take for granted that our thoughts (beliefs, desires, intentions, and so forth) are directly involved in the causal production of what we do. When we take a closer look at explanations of behavior, however, things turn out to be somewhat more complex. Indeed if, on commonsense grounds, it would never occur to us to deny that we do what we do because of what we think, it is all but clear, from a metaphysical point of view, just how thoughts could directly cause behavior. (3)
A widely-held view of behaviorwhich we may term the standard view of behavioridentifies behavior with neurophysiologically-produced bodily movements. A few moments of reflection should suffice to convince anyone of the plausibility of the view. Whatever the details may be, it seems quite reasonable to claim that when we behave purposively, the movements of our bodies are brought about by complex neurophysiological mechanisms and processes. While this approach does not rule out the causal involvement of thoughts in the production of behavior, it certainly forces defenders of the commonsense view to show how thoughts and neurophysiological causes are related.
According to proponents of the standard view of behavior, thoughts are causally efficacious insofar as they supervene upon the neurophysiological states that causally explain behavior. In other words, mental causation is thus possible only if mind/brain supervenience obtains. To see why, we may look at the following example. Assume upon thinking of a friend you acquire, at t1, the intention to call her; a moment later, at t2, you pick up the telephone and dial her number. The arm and finger movements involved in calling your friend are brought about, we assume, by a complex process originating somewhere in the output-producing structures of your brain. Barring causal overdetermination, the sufficient cause of your behavior will be traced back to some neurophysiological event occurring in your brain at t1.
Where does that leave your intention to call your friend? Surely it would be highly counterintuitive to deny that your intention to call her caused you to pick up the telephone and dial her numberhad you not entertained the intention to call her, you simply wouldnt have called. As already mentioned, we all experience cases of mental-to-physical causation on a daily basis, and any remotely plausible theory of behavior must account for such cases. The present view of behavior acknowledges and explains the causal efficacy of your intention to call your friend by claiming that it supervenes on the neurophysiological state-type that causally explains the movements of your arm and finger. The relation between your intention to call your friend and its subvenient basea case of mind/brain supervenienceis realized by the neurophysiological event causing the movements of your arm and finger. Mind/brain supervenience is thought to provide the best account for the possibility of mental causation. Let us therefore turn to examine mind/brain supervenience a little closer.
The idea that higher-level, mental properties supervene on lower-level, neurophysiological ones is thought to solve what is known as the exclusion problemthe problem of accounting for the genuine causal authority of higher-level properties (such as mental properties) in the production of purposive behavior. The example presented in the previous section, simple as it may be, illustrates the central problem at issue. If your intention to call your friend supervenes (4) on the neurophysiological state-types that causally explain your behavior, and if those neurophysiological state-types have the relevant causal powers, then, according to the standard view of behavior, your intention to call your friend inherits those causal powers, and thus causes your behavior. (5) This works because supervenience guarantees that there can be no difference among higher-level, supervenient state-types without a difference among lower-level, subvenient state-types. Had you entertained a different intention, its subvenient, neurophysiological base would have been different, and you possibly would have behaved differently. (6) However that may be, the view faces notorious problems, and it will be useful to quickly rehearse those before we move on.
Within a materialistic framework of the kind assumed hereand particularly on the standard view of behaviormind/brain supervenience solves the exclusion problem so long as the individuation modes of mental state-types and brain state-types are kept in phase. This peaceful harmony, however, was disrupted by so-called Twin cases. Everyone knows the story, so I wont bother to spell it out. The disruptive effect of the Twin Earth Syndrome may be represented as follows:
M stands for mental state-types; B stands for brain state-types; ?? stands for supervene upon; (R) stands for relationally individuated; and (~R) stands for nonrelationally individuated.)
(i) represents a situation where mental state-types are individuated relationally whereas brain state-types are not. The classic H2O/XYZ case ran on just such a disruptionwhether your environment contains H2O or XYZ will essentially affect some of your mental state-types without affecting your brain state-types; so there can, according to the H2O/XYZ story, be differences among mental state-types without corresponding differences in brain state-types, a clear violation of mind/brain supervenience. (7) Hence the return of the exclusion problem. Hence the threat of the causal inertness of the mind. As far as I can tell, this breakdown of the supervenience relation has led to one of the following strategies: (i) abandoning mind/brain supervenience and working out a form of dualism to save mental causation; (ii) abandoning mental causation altogether and working out a form of eliminative materialism; (iii) restoring mind/brain supervenience by keeping individuation modes in phase. I propose to ignore (i) and (ii) and focus on the latter course of action.
There are of course two distinct ways of keeping individuation modes in phase: one can restore mind/brain supervenience by claiming that in spite of the commonsense tendency to individuate mental state-types relationally, the way out of the exclusion problem consists in individuating mental state-types nonrelationally, as depicted by (ii) below. The other way consists in retaining the commonsense mode of individuation for mental state-types, and claim that brain state-types should be individuated relationallyas depicted by (iii) below.
The arrangement depicted by (ii) restores mind/brain supervenience by opting for the nonrelational individualtion of mental state-types and brain state-types. The problem usually associated with (ii) is its demand of a narrow notion of content. A number of philosophers have tried to articulate such a notion over the past decade or so, but a great deal of controversy concerning the very possibility of such content remains. However that may be, narrow content still has its fans, and I do not intend to argue against the view here. Instead, I propose to move on and examine a different way of restoring mind/brain supervenience. The strategy I shall develop consists in assuming the relational individuation of mental state-types and focusing on the individuation mode of their subvenient base types.
Another way of preserving mind/brain supervenience is to grant the relational individuation of mental state-types and to claim that brain state-types are also individuated relationally, as represented by (iii). A peculiarity of this view is that it dismantles the Twin Earth problem by ruling out Twin cases on the grounds that they involve worlds that are far too remote to merit any attention. If indeed brain state-types are relationally individuated, it will be quite impossible for two individuals embedded in different environmental circumstances and causal histories to be neurophysiological twinsexcept perhaps in worlds that are radically different from ours. One should further note that, strictly speaking, the worlds left out by (iii) are precisely those where the kind of solipsism Twin cases were targeting obtains.
(iii) restores mind/brain supervenience in a way that is compatible with a form of externalism. On this view, differences in a subjects environment that affect his mental state-types would also affect his brain state-types, and the kind of disruptions portrayed in (i) would simply be explained away (and, as mentioned above, worlds where disruptions remain would be a sure sign of remoteness.) Prima facie, (iii) preserves mind/brain supervenience, and thus provides grounds, in principle at least, for a coherent view of mental causation. But as I now want to stress, it makes very little sense to individuate brain state-types relationally.
Jerry Fodor believes that the relational individuation of brain state-types is a "silly," "grotesque" and "mad" idea (Fodor, 1987). I agree. Essentially, to individuate brain state-types relationally would amount to claiming that a brain state-types relational properties effect real, essential changes among its intrinsic, causal properties. But can we really claim that, say, being exactly 1,200 miles south of the Eiffel Tower effects a real change in the brains of those who instantiate that and other so-called Cambridge properties? Wouldnt this be like saying that since you gained ten pounds, my growing ten pounds lighter than you effected a real, essential change in me? In light of such cases, the arrangement depicted by (iii) does indeed look completely hopeless. But what I want to argue now is that we dont really need to individuate brain state-types relationally to solve the exclusion problem and restore mind/brain supervenience. All we need is a subset of nonrelationally individuated brain state-types that have a causal history that traces back to relevant environmental circumstances and that are causally involved in the production of their bearers behavior. Such brain state-types would be, in part, at least, determined by and dependent upon the specific ways their causal histories would affect them. As I mentioned at the outset, I propose to refer to this situation as nonlocal sensitivity.
Fodor grants that there are, of course, causal relations that hold between the environment and an individuals brain states, but those causal relations, he claims, do not affect the latters intrinsic, causal properties. "[T]he causal histories of our brain states" he writes, "is not of the right sort to effect a difference in the causal powers of our brains." (Fodor, 1987: 157-58.) I tend to disagree with Fodor on this point. Why couldnt there be cases where brain state-types are intrinsically affectedthat is, affected in their intrinsic, causal propertiesby relevant environmental circumstances and causal histories? John Heil, for one, has claimed recently that it is quite natural for the neurophysiological state-types on which mental state-types supervene to have their narrow causal properties affected by their external circumstances and causal histories. He writes
Heil is exactly right on this point. Why couldnt there be brain state-types whose causal properties are affected by their bearers environmental circumstances and causal histories? Why should the intrinsic, causal properties of brain state-types be entirely cut off from the world? This deeply entrenched idea that all of a brains intrinsic, causal properties must be locally sensitive strikes me as highly implausible. Once the relational individuation of brain state-types is clearly ruled out, it becomes possible to conceive of a subset of brain state-types that are at once nonrelationally individuated and nonlocally sensitive.
Surely, there are complex brain structures whose job is to mediate between an organisms environmental circumstances and its output-producing structures. Yet, the brain state-types that make up those structures neednt be relationally individuated. As long as we understand nonlocal sensitivity to involve a brain state-types intrinsic properties, we can avoid all the maddening scenarios alluded to above. If we grant that some complex brain state-types are nonlocally sensitive, we then have an appropriate subvenient base for mental state-types, and can thus restore mind/brain supervenience and claim to have a solution to the exclusion problem.
I propose that we concieve of mind/brain supervenience as follows:
As was the case with (iii), the arrangement depicted by (iv) rules out Twin cases in the actual and all nearby worlds. This is implied by [B (~L)], of coursean implication that the solipsists will have a rough time accepting, for what it basically says is that, yes, solipsistic worlds are possiblebut not here or anywhere near. As I mentioned at the outset, solipsists will stick with something like arrangement (ii) above, and claim that theirs is the best way out of the exclusion problem. Thats fine, because nothing Ive said so far shows that mental state-types cannot be individuated nonrelationally. Yet, the claim that they can be so individuated remains controversial because of the notion of narrow content. In the meantime, as long as we concieve of the subvenient base of mental state-types as nonlocally sensitive brain state-types, we can rest assured that our thoughts are firmly anchored in the world and thus have all the causal authority we commonsensically take them to have.
Baker, L. R. (1993). Metaphysics and mental causation. Heil & Mele (1993), 73-95.
Burge, T. (1993). Mind-body causation and explanatory practice. Heil & Mele
Dretske, F. (forthcoming). Minds, machines, and money: what really explains behavior.
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Fodor, J. (1987). Psychosemantics. MIT Press.
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Kim, J. (1992). Multiple realization and the metaphysics of reduction. Philosophy and
Phenomenological Research, 52, 1-26. Reprinted in Kim (1993), 309-335.
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Notes(1) Those with a solipsistic bent will of course prefer to stick with nonrelational individuation all the way up, and claim that narrow content really is the way out of the exclusion problem. I propose to mostly ignore that perspective, and assume the relational individuation of mental state-types. I shall not, then, offer any argument against narrow content, and so must grant the plausibility of the view I here dub solipsistic. (2) A number of complications arise here, for, as Kim has recently argued, the supervenience relation itself may be seen to get in the way of a solution to the exclusion problem. I agree with Kim and others that only a strenghtened, reductionist form of the supervenience relation will do the job. I cannot, however, pursue these issues in the present context. For more on this and related issues, see Kim (1992; 1995) and Stalnaker (1997). (3) The claim that we should turn to metaphysics to settle a number of issues of mental causationincluding the question of the epiphenomenal character of the mentalmeets with strong opposition from philosophers who claim that explanations and explanatory practices are best suited to deal with those issues. Again, I cannot address the debate in the present context. For details, see Baker (1993), Burge (1993), Dretske (forthcoming), and Kim (1995), among others. (4) The supervenience thesis needed here must be understood as a form of reductionist thesis. Indeed, in order to avoid the threat of exclusion, your intention must be, in some relevant sense, the neurophysiological state-type that causally brings about your behavior. (5) Talk of properties and types playing a causal role is somewhat misleading, but I use it purely for ease of exposition. I do favor an extentionalist view of causation according to which it is events that enter causal relations. However, I take events to be instancings of a property by an object at a time, and claim that property-instancings, as opposed to properties or types themselves, enter relations as causes and effects. When saying that a property (P) plays a causal role in bringing about an effect (e), I should be understood as saying that an instancing of P causes e, and that reference to the property (P) may enter a causal explanation of the bringing about of e. (6) Possibly because you could have entertained, say, the intention of calling someone else, in which case you would have performed the same type of movements. On the other hand, you could have entertained the intention of writing to your friend, and in that case would have behaved differently. (7) So, strictly speaking, ?? in (i) should be replaced by ~??which stands, of course, for do not supervene upon.