Some Potential Problems with SS mn

In this final section, I consider some potential problems that arise for the non-reductive physicalist from this formulation of supervenience. Firstly, one could argue that this formulation of supervenience is too strong. For example, one could argue that as an a posteriori doctrine about the actual world, physicalism should not a priori rule out the possibility of things such as

Cartesian souls, zombies and ghosts. However, according to the formulation of SSmn proposed above, such non-physical entities could not, as a matter of metaphysical possibility, exist.

I think that we can solve this problem by appealing to a point that I made in the previous chapter (see footnote 1), which was that physicalism, as it follows from the Causal Argument, does not necessarily entail the view that everything is physical, but need only entail the view that everything that interacts causally in the world must be identical to, or supervenient on the physical. This is because causal closure, which features as a premise in the Causal Argument, states that every physical effect has a sufficient physical cause, but leaves open the possibility that there may be non-physical properties, such as mathematical, or even spiritual properties, so long as these properties do not exert any causal influence on the world. The non-reductive physicalist who is persuaded by the Causal Argument is not therefore committed to the view that non-physical

entities, such as disembodied souls, could not as a matter of metaphysical possibility exist, but is only committed to the view that if these non-physical entities did exist they could exert no causal influence in the world. SSmn is not

therefore in tension with the a posteriori nature of physicalism.22

The second problem that needs to be addressed is whether SSmn entails

the reduction of supervenient properties on their subvenient base properties. This issue is extremely important for the non-reductive physicalist, since if it turns out that the form of supervenience that I argue is a minimal commitment of non- reductive physicalism entails reduction, then non-reductive physicalism will be a priori ruled out by this definition of supervenience.

Now, although I have argued that SSmn entails the strong metaphysical dependence and entailment of supervenient properties on their subvenient bases, it is not clear that reduction straightforwardly follows from this form of supervenience. In order to see this, consider the following points.

Firstly, note that SSmn is consistent with the multiple realizability of supervenient properties, i.e. consistent with the idea that a supervenient property from set A will supervene on a variety of subvenient bases from set B, such that it will not be possible to type-identify and hence reduce supervenient property

types with subvenient property types. Although the issue of multiple realization is by no means straightforward, it does seem that multiple realization makes type- reduction, even with SSmn, implausible.

22 _{There is a further worry, which is highlighted by Papineau (2009), which is that if it were true} that non-physical properties, such as mathematical properties, did exist but did not exert any causal influence on the world it is not clear how we could acquire any knowledge of them, given the plausible assumption that we normally acquire knowledge of the external world through some kind of causal interaction between properties and our cognitive system. However, as Papineau (Ibid) points out, so long as it is plausible that there are non-causal forms of knowledge, such as a priori knowledge, the physicalist can avoid this problem.

What about reduction at the level of token instantiated properties? SSmn

states  that  every  particular,  or  ‘token’  instantiation  of  a  mental  property,  such  as  

the property of having a desire for a cup of tea, call it D1, which causes some

physical effect, for example, reaching behaviour B1, is dependent on and entailed

by a token instantiation of a physical property, for example, N1, which is also a

cause of B1. Does this degree of supervenient dependence and entailment mean

that D1 is thereby reducible to N1? Not necessarily.

In order to see   this,   consider   Kim’s   (1984)   point   that   as   an  epistemic

activity, reduction does not necessarily follow from this level of entailment and dependence. For example, by knowing that D1 supervenes on N1 with

metaphysical necessity and that it is entailed by and wholly dependent on N1 we

do not thereby acquire an explanation of D1, for example of its intentional nature.

Moreover, as Kim points out, even though SSmn does guarantee that every mental property will be entailed by and wholly dependent on some physical property, it does not follow that those mental-to-physical relationships will be available to analyse for reductive or explanatory purposes. As Kim explains,

“Where   strong   supervenience   obtains,   [this]   gives   us   the   assurance   that  

such connections in the form of necessary equivalences are there to be discovered, without of course the further assurance that we shall succeed in discovering them or that they will be representable in an explanatory

What both of these points suggest is that although SSmn entails the

metaphysical dependence and entailment of supervenient properties on their subvenient bases, this does not necessarily entail the reduction of those supervenient properties. SSmn is not therefore incompatible with non-reductive

physicalism.

One final point that I will consider is whether SSmn entails that

supervenient   properties   are   nothing   ontologically   ‘over   and   above’   their  

subvenient bases. Or as McLaughlin and Bennett (Summer 2010) put it, whether SSmn entails that   supervenient   properties   are   ‘ontologically   innocent’   with  

respect to their subvenient bases. It is clear that the non-reductive physicalist

requires  the  ‘ontological  innocence’  of  supervenient  properties  in  relation  to  their  

subvenient bases, since to accept any kind of ontological distinction between mental and physical properties would be to endorse a form of dualism.

However, if the implications that have been discussed thus far really are implications of SSmn it would seem to rule out the possibility that supervening mental properties could be anything ontologically over and above their subvenient bases, in accordance with the requirements of physicalism. This is because the degree of modal force with which SSmn holds, which ensures that supervenient properties are entailed by and wholly dependent on physical properties, guarantees that those supervenient properties could not be ontologically distinct from those subvenient base properties.

In this section I have argued that the non-reductive physicalist is minimally committed to a form of strong supervenience, which holds with metaphysical necessity across all possible worlds and which implies that mental properties are entailed by and dependent on physical properties. I argued that any

weaker form of supervenience would not be suitable for the purposes of the non- reductive physicalist, since it would be consistent with dualism. I finally addressed some potential problems with this form of supervenience, but argued that the non-reductive physicalist can avoid them. It is therefore possible to conclude that SSmnis a minimal commitment of non-reductive physicalism that

cannot be rejected in order to avoid the exclusion problem.