Could a classical theist be a physicalist? Although a negative answer to this question
may seem crashingly obvious, it turns out that a case can be made for the consistency of a
variant of classical theism and global supervenience physicalism. Although intriguing, the
case ultimately fails due to the weakness of global supervenience as an account of the
dependence of mental on physical properties.
Physicalism is popular these days, and to a lesser extent so is classical theism. It
should therefore come as no surprise that a number of theists are bent on combining theism
with physicalism. But could a classical theist be a physicalist? Is this a
coherent doctrinal combination? The classical theist affirms the metaphysically necessary
existence of a concrete, purely spiritual, being upon which every other concrete being is
ontologically dependent. The physicalist, however, is committed to the proposition that
everything, or at least everything concrete, is either physical or determined by the
physical. To be a bit more precise, physicalism is usefully viewed as the conjunction of
an 'inventory thesis' which specifies physicalistically admissible individuals
and a 'determination thesis' which specifies physicalistically admissible properties.(1)
What the inventory thesis says, at a first approximation, is that every concretum is
either a physical item or composed of physical items. As for the determination thesis,
what it says is that physical property-instantiations determine all other
property-instantiations; equivalently, every nonphysical property-instantiation supervenes
on physical property-instantiations. These rough characterizations suggest that theism and
physicalism logically exclude one another. If God as classically conceived exists, then
the inventory thesis is violated: not every concrete entity is either physical or composed
of physical items. And if God exists, it would also appear that the determination thesis
is flouted: God's instantiation of his omni-attributes does not supervene on His
instantiation of any physical properties: He has none. So at first glance it seems almost
crashingly obvious that the classical theist cannot be a physicalist.
But this talk cannot end just yet. For when we get down to the details of formulating
precise versions of both the inventory and determination theses, it turns out that there
is a way to attempt the reconciliation of theism and physicalism. It is the viability of
this way that I aim to explore. But first some background.
Towards Nonreductive Physicalism
I will take it for granted that a plausible version of physicalism cannot be either
eliminativist or reductionist. The view that beliefs and desires enjoy the status of
witches and goblins, that consciousness is as fabulous as phlogiston, and that Joe
Sixpack's rooting around in the refrigerator cannot be explained folk-psychologically by
saying that he wants a beer and believes one can be found there, is a view with little to
recommend it beyond its shock value. Now if mental phenomena are real, which they
obviously are, one way to assure both their reality and their scientific respectability is
by identifying them with what are undeniably real and doubtlessly respectable, namely,
physical phenomena. Thus the type-type identity theorist identifies mental properties with
physical properties of the sort instantiated in our brains. This sort of reductionist
position is no longer widely accepted for various reasons, the most politically correct of
which no doubt is that the view issues in the dreaded consequence of 'species-chauvinism.'
For if pain, to coin an example, is identical to Delta-A fiber stimulation, then only
beings with our neurophysiological constitution could possibly be in pain. And that does
seem strongly counterintuitive.
But if we eschew both eliminativism and reductionism, what options are left for the
would-be physicalist? The problem for the physicalist is that he must avoid both
eliminativism and reductionism but without falling into epiphenomenalism, emergentism, or
(of course) substance dualism. Epiphenomenalism cannot accommodate the fact that mental
phenomena sometimes enter into the etiology of physical events, while emergentism and
substance dualism leave physicalism behind. The problem is to somehow secure the reality,
the causal efficacy, and the irreducibility of the mental while maintaining the dependence
of the mental on the physical. What the physicalist needs, it seems, is a dualism of
properties together with the idea that the mental properties somehow nonreductively depend
on the physical ones. But how articulate this dependency relation?
Strong Supervenience
Enter supervenience. The basic idea is that mental properties are not identical with,
but merely supervene upon, physical properties in the way in which ethical properties have
been thought (by G. E. Moore, R. M. Hare, and others) to supervene upon natural
properties. Suppose A and B are both ethically good. It does not follow that there is any
one natural, non-disjunctive, property with which goodness can be identified. Perhaps A is
good in virtue of being brave and trustworthy, whereas B is good in virtue of being
temperate and just. Goodness is in this sense "multiply realizable." A and B are
both good despite the fact that their goodness is realized by different natural
properties.(2) Nevertheless, (i) a person cannot be good
unless there is some natural property in virtue of whose possession he is good, and (ii)
if a person is good in virtue of possessing certain natural properties, then anyone
possessing the same natural properties must also be good. Given that A-properties
supervene upon B-properties, the "supervenience T-shirt" might read: "No
A-property without a B-property" on the front; "same B-properties, same
A-properties" on the back. As Jaegwon Kim puts it, "The core idea of
supervenience as a relation between two families of properties is that the supervenient
properties are in some sense determined by, or dependent upon, the
properties on which they supervene."(3)
Kim's preferred way of cashing this out is in terms of strong supervenience.
Let A and B be families of properties closed under such Boolean operations as
complementation, conjunction and disjunction. A strongly supervenes on B just in
case:
(SS) Necessarily, for any property F in A, if any object x has F, then there exists a
property G in B such that x has G, and necessarily anything having G has F.
Applying (SS) to physicalism, we may define the determination thesis of strong
supervenience physicalism as the view that, necessarily, (i) for any mental property M, if
x has M, then there is physical property P such that x has P, and (ii) necessarily,
anything having P has M. Now there are many questions one can raise about (SS), but for
present purposes we
need only decide whether (SS)-physicalism allows the truth of theism. I think it is
clear that it does not. For clause (i) of the definition implies that for each mental
property God has, He has a physical property — but classically God has no physical
properties.
Global Supervenience
So let's consider how theism fares under global supervenience. What global
supervenience says is that
(GS) If any two (physically possible) worlds are B-indiscernible, then they are
A-indiscernible.
To say that two worlds are B- or A-indiscernible is to say that they share the same
total pattern of distribution of B- or A-properties. The determination thesis of global
supervenience physicalism, then, amounts to the claim that if any two worlds are
physically indiscernible, then they are mentally indiscernible. There cannot be a mental
difference between two worlds without a physical difference.
Peter Forrest has argued that global supervenience physicalism is compatible with the
belief in a non-physical, non-contingent god if we are willing to make certain speculative
assumptions.(4) Given that God as classically conceived
exists in every metaphysically possible world, no two worlds differ in point of the divine
existence. And if God can create only physical things — this is one of the
speculative assumptions — then no two worlds in which God creates will differ without
differing in a physical respect.(5) Thus there appears to be
a variant of classical theism that is compatible with a version of supervenience
physicalism. For what global supervenience physicalism says is that if there is a mental
difference between two worlds, then there is a physical difference between them. If God
exists in every possible world, and creates only physical things in the worlds in which He
creates anything, then His existence and actions never contribute to a mental difference
between worlds, and so His existence is consistent with the constraint that (GS) lays
down.
To the objection that this amounts to a violation of physicalism's inventory thesis,
the committed global supervenience physicalist might respond that if the existence of
abstract necessary beings (Fregean propositions, numbers, sets of the latter...) is
consistent with the inventory thesis, why shouldn't the existence of a concrete necessary
purely spiritual being be equally consistent with it? Perhaps it could be said that the
inventory thesis is a claim solely about the world of space-time so that God, angels and
abstracta are not counterexamples to it.(6) Indeed, it could
be argued that physicalism is an empirical theory and that therefore its inventory thesis
should remain silent about non-empirical entities. Or perhaps it could be argued that
physicalism is exhausted by the determination thesis — every property-instantiation
supervenes on physical property-instantiations — so that the inventory thesis doesn't
come into it at all. Forrest implies as much: "...supervenience physicalism amounts
to saying that any two possible worlds exactly resembling each other in all physical
respects exactly resemble each other in all respects."(7)
So understood, physicalism places no constraint on what can exist; it puts a constraint on
which properties can be instantiated, namely, only those for which there is a physical
subvenience base. In any case, it would be dialectically ineffective to respond to Forrest
by saying that no physicalism worthy of the name can admit the existence of God,
reasonable as that sounds. For that would be to beg the question against him.
Nevertheless, Forrest's reconciliation of physicalism with theism is unsatisfactory,
for at least five reasons. First, a variant of classical theism in which God cannot create
non-physical things is a variant in which angels are not even possible. And so Forrest's
argument is of no use to a Christian or an Islamic classical theist who would be a
physicalist.
A second and more important reason is that it is unclear what it could mean for God's
mental properties to supervene globally on physical properties. Consider a pair of worlds
in which there are physical objects but no minds except God. In these worlds the mental
properties globally supervene upon the physical properties because there is no mental
difference between the worlds and hence no mental difference without a physical
difference. Now global supervenience is supervenience (in the way in which 'as-if'
intentionality is not intentionality), and supervenience is supposed to capture
the ideas of dependence and determination. But none of God's intrinsic properties depends
for its instantiation on the instantiation of any physical property. There is no sense in
which any of God's intrinsic properties need physical properties to realize them.
If this isn't obvious, think of a world in which God exists but nothing physical exists.
And no physical property is such that its instantiation determines (suffices for)
the instantiation of any of God's intrinsic properties. If per impossibile God
were not to exist, or exist bare of properties, the instantiation of no physical property
would make him exist or make him have any property. Furthermore, the only sense in which
God's intrinsic mental properties vary with physical properties is the trivial sense in
which, since they do not vary, they satisfy the conditional, "If there is a
variation in mental properties, then there is a variation in physical properties."
Thus there is no nontrivial sense in which God's mental properties supervene on physical
properties, and thus in our pair of worlds, no nontrivial sense in which mental properties
in those worlds supervene on the physical properties. So although (GS)-physicalism permits
the existence of a non-contingent god, this permissiveness is purchased at the expense of
eviscerating the concept of supervenience of the notions of dependence and determination
that it was introduced to express. (GS) is just too weak and liberal to be of use in
formulating nonreductive physicalism.
Along the same lines, and apart from the God question, Kim has persuasively argued that
global supervenience is too weak a notion to capture the idea, crucial to physicalism,
that mental properties are dependent upon, or determined by, physical properties.(8)
For "...it is consistent with this version of materialism [global supervenience
physicalism] for there to be a world which differs from this world in some most trifling
respect (say, Saturn's rings in that world contain one more ammonia molecule) but which is
entirely devoid of consciousness, or has a radically different, perhaps totally irregular,
distribution of mental characteristics over its inhabitants (say, creatures with brains
have no mentality while rocks are conscious)."(9) Kim's
point is that on (GS), the least physical difference between any two worlds allows as wild
a psychological difference between them as you care to imagine. But that seems to make
hash of the idea that the mental is determined by, and dependent upon, the physical. A
version of physicalism that allows a world triflingly different from ours to contain rocks
that are conscious and human beings that are not is presumably not a version of
physicalism according to which the mental is determined by the physical in any sense that
inspires confidence. Kim also points out that "...global psychophysical supervenience
is consistent with there being within a given world, perhaps this one, two physically
indistinguishable organisms with radically different psychological attributes."(10)
There is a further reason why global supervenience is too weak to be of use in
formulating a serious version of physicalism: it allows for Cartesian psychophysical
supervenience, or what we might call supervenience dualism. For the global supervenience
of mental on physical properties is consistent with the mental properties being possessed
by irreducibly mental substances and the physical properties being possessed by physical
substances. There is nothing in the concept of global supervenience to rule out multiple
domain supervenience in the way in which (SS) and (WS) do rule out multiple domain
supervenience.(11) That is, if mental properties strongly or
weakly supervene on physical ones, then necessarily if an individual has a mental
property, then that very same individual has a physical property, and presumably not just
any old physical property, but one that "realizes" the mental property; whereas
if mental properties globally supervene on physical ones, there is the possibility that
the set of possessors of the mental properties and the set of possessors of the physical
properties be disjoint. But this possibility would of course tend to eviscerate the idea
that the physical properties "realize" the mental properties: To say that my
mind cannot have a mental property unless my brain has a physical property, and that there
cannot be a difference in mental properties without a difference in physical properties is
not by a long shot to say that the physical properties 'realize' the mental properties. It
is merely to say that my mental properties 'co-vary' with my physical properties. If
supervenience is nothing more than covariation, then it cannot get the length of
dependence, determination or realization.
The point here is not that (GS)-physicalism allows inventory-violating Cartesian
thinking substances, for I have provisionally conceded to what I take to be Forrest's
position that physicalism is perhaps exhausted by the determination thesis so that it need
take no stand on inventory. My point is that (GS) fails to nail down an adequate concept
of determination.
My conclusion, then, is a conservative one. The classical theist can find no aid and
comfort in the fashionable precincts of supervenience physicalism.
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