I
In what follows, 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 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-types—namely, those involved in the production of
purposive behavior—are nonlocally sensitive, where by ‘nonlocal
sensitivity’ I understand cases where relevant causal histories and environmental
circumstances effect a difference in some of an organism’s 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-type’s 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 solipsist’s 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.
II
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 behavior—which we may term the ‘standard view of
behavior’—identifies 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 number—had you not entertained the intention to
call her, you simply wouldn’t 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
base—a case of mind/brain supervenience—is 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.
III
The idea that higher-level, mental properties supervene on lower-level,
neurophysiological ones is thought to solve what is known as the ‘exclusion
problem’—the 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 here—and particularly on the
standard view of behavior—mind/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 won’t bother to spell it out. The
disruptive effect of the ‘Twin Earth Syndrome’ may be represented as follows:
(i)
M — (R)
??
B — (~R)
‘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
disruption—whether 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 relationally—as depicted by
(iii) below.
(ii)
M — (~R)
??
B — (~R)
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.
(iii)
M — (R)
??
B — (R)
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 twins—except 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 subject’s 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-type’s 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?
Wouldn’t 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 don’t 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 individual’s brain states, but those causal relations, he claims,
do not affect the latter’s 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 couldn’t there be cases where brain state-types are
intrinsically affected—that is, affected in their intrinsic, causal
properties—by 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
Every actual physical condition has some history or other. When mental
characteristics have aetiological significance for behaviour (excluding cases of
overdetermination) agents are such that, were they to differ mentally, they would behave
differently. Given the supervenience hypothesis, this means that, were these agents to
lack the historical features in virtue of which their physical conditions now realise
these mental characteristics, those physical characteristics—narrowly
concieved—would be different, and, in consequence, their narrow causal capacities
would be different. (Heil, 1992: 146-7)
Heil is exactly right on this point. Why couldn’t 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
brain’s 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
organism’s environmental circumstances and its output-producing structures. Yet, the
brain state-types that make up those structures needn’t 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:
(iv)
M — (R)
??
B — (~L)
(‘~L’ stands for ‘nonlocally sensitive’.)
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 course—an
implication that the solipsists will have a rough time accepting, for what it basically
says is that, yes, solipsistic worlds are possible—but 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. That’s
fine, because nothing I’ve 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.
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