Mental properties supervenience

What I want to focus on here is Davidson s argument that his view does not lead to the epiphenomenalism of mental properties. Davidson seems to argue here that the supervenience of mental properties on the physical will ensure their causal efficacy. For example, Davidson says ... 

If supervenience holds, psychological properties make a difference to the causal relations of an event, for they matter to the physical properties, and the physical properties matter to causal relations. It does nothing to undermine this argument to say But the mental properties make a difference not as mental but only because they make a difference to the physical properties . Either they make a difference or they don t if supervenience is true, they do (1993 14). 

Davidson, I think, is led to this particular line of defense because of his views about causation. Davidson holds an extensionalist view of causation - i.e., that causation is a relation between non-abstract particular events. Thus he says, But it is also irrelevant to the causal efficacy of physical events that they can be described in the physical vocabulary. It is events that have the power to change things, not our various ways of describing them (Davidson 1993 12). Since it is events that are causes, then any properties that are relevant to what a particular event causes are causal properties. Davidson says, But properties are causally efficacious if they make a difference to what individual events cause, and supervenience ensures that mental properties do make a difference to what mental events cause (1993 15). So since mental properties supervene on physical properties, and physical properties make a difference to what an event causes, mental properties also make a causal difference. 

Thus, Davidson s claim that supervenience saves mental causation falls short. Davidson is wrong to think that the question, hi virtue of which properties did event A cause event B makes no sense. To save AM fi om the epiphenomenalism of mental properties, we need a way to show how it is possible for causation to be in virtue of mental properties. The question is whether the anomalism of the mental will make it impossible for mental properties to be the one s in virtue of which events are causes. 

Let us now take a preliminary look at how to make sense of causation in virtue of irreducible mental properties. If we are going to assume, for the purposes of this discussion, that Davidson has not quite done enough to get property causation, then we need to find a different way to make sense of property causation. Before we can do this, we need to make sure that this project is even possible. If strict laws will rule out causation in virtue of irreducible mental properties, then it is hard to see how any approach other than Davidson s appeal to supervenience and non-strict laws could possibly save property causation. If, however, strict laws do not rule out causation in virtue of irreducible mental properties, then we will be in a position to try to find out how irreducible mental properties can be causal. 

This type of objection to nonreductive materialism is central to the work of Jaegwon Kim. Kim discusses this objection extensively in the various versions of his exclusion argument or supervenience argument. He holds that the only way to give mental properties a causal role is to functionally reduce them to physical properties, since physical causation will always rule out causation in virtue of irreducible mental... 

If, however, we reduce mental properties to physical properties, then mental properties will simply inherit the causal powers of their supervenience bases and will thus be causal in this derivative sense. 

This principle could be taken to mean that every good causal story we can tell has to be couched in physical terms or that all causation is always in virtue of physically definable or reducible properties. Taken this way, however, this principle would just beg the question against nonreductive materialism. Under physical causal closure, it is not that we can never invoke physically irreducible higher-level properties as causes for a physical event. We may very well cite some irreducible mental property as the cause of some physical event. The point is that this mental property, if it is to be causal, must somehow be anchored in the physical world. It must be tied to the physical by some sort of supervenience or realization relation. This close tie to the physical will always make it possible, in principle, for us to tell a causal story in terms of physical properties, even though the best causal story might not always refer only to physical properties. Thus, we will never be forced to go outside the physical domain and refer to physically irreducible properties in order to find a sufficient cause for a physical event. So the principle of physical causal closure requires that if we pick any physical event, it will always be possible, in principle, for us to find a purely physical causal chain for that event. So if we take any physical event P, we should be able to find some property or group of properties P, such that P is physical and P is a sufficient cause for P. ... 

The second assumption that leads to the exclusion problem is the idea that any physicalist view is committed to some sort of notion of mind-body supervenience. There are many different notions of supervenience, but at minimum, a physicalist must hold that every mental property has some sort of physical base which instantiates it. The mental depends, for its existence, on some sort of underlying physical state and does not constitute its own ontologically independent domain (Kim 1998 41). Thus, if we take any mental property M, it will have some underlying set of physical properties P on which it supervenes. ... 

Kim formulates what he takes mind-body supervenience to entail as follows Mind-body supervenience Mental properties supervene on physical properties in the sense that if something instantiates any mental property M at t, there is a physical base property P such that the thing has P at t, and necessarily anything with P at a time has M at that time (1998 39). ... 

But recall that the exclusion principle is not restricted to simply mental properties. The principle holds that no event can have two distinct properties unrelated by reduction as causes, if one of the properties is a sufficient cause. But the ball sorter example is a clear case where we have two distinct causes, unrelated by reduction. The lower-level property is a sufficient cause, yet the higher-level property is clearly a causal property as well. If the revised exclusion principle were true, it would rule out not just the causal efficacy of mental properties, it would also force us to hold that the property of size cannot be causally efficacious with respect to the balls sorting. In fact, we would have to say that no distinct and irreducible higher-level supervenient property is ever causal, and that all real causation always happens at the lower level. This is an unpleasant result and not one that we should be willing to accept. Thus, we ought to reject the exclusion principle on these grounds. 

Kim s criticisms of nonreductive materialism attempt to show, primarily through the use of his exclusion or supervenience argument, that irreducible mental properties carmot be causal properties. I argue, against this, that the reductionist picture of causation created by the exclusion principle is deeply mistaken, and I offer an accoxmt of how irreducible mental properties can be causal properties. 

If we are prepared to go for a functionalization of all mental properties, we will be embracing an all-encompassing reductionism about the mental, and this will solve the problem of mental causation. That s the good news. On a reductionist picture of this sort, however, the causal powers of mental properties turn out to be just those of their physical realizers, and there are no new causal powers brought into the world by mental properties. Many will consider that bad news. But the real bad news is that some mental properties, notably phenomenal properties of conscious experiences, seem to resist functionalization, and this means there is no way to account for their causal efficacy within a physicalist scheme. These properties are not able to overcome the supervenience argument, (pp. 118—19)... 

Accept that mental properties are causal idlers, but sweeten the pill by arguing that causal idlers that supervene on causally potent properties are not a problem or anyway not a problem to the extent that nonsupervening causal idlers are. On this option, the bogey of epiphenomenal-ism is the conjunction of causal impotence with lack of supervenience it is the conjunction that sinks dualism. 

At the very least, M and P must be related by supervenience. However, it may be that mere supervenience is not enough to give us an adequate accoimt of mental causation within a physicalist framework. We might want to hold a view like Davidson s, where not only does M supervene on P, but P realizes M, and M and P are properties of a single event. So as properties, M and P are distinct, but as event, M and P are token identical. Whether physicalism requires mere supervenience, a picture like Davidson s with realization and event identity, a functional reduction of M to P as Kim advocates, or a fullblown type identity of M and P will be discussed shortly. 

I do not think, therefore, that supervenient causation is a viable account of the causal powers of extrinsic mental statesd If what I believe is a genuine relational property of me, then it might, in some local way, weakly supervene on my intrinsic physical properties, but I do not see how it can display the kind of dependence on my intrinsic physical properties that would tempt us to say that it causes whatever the physical states on which it supervenes causes. 

Now some dependence claims are transparently generated, or at least supported by, reflection on the concepts whose use characterises the supervenient domain. Take, for example the view associated with G.E. Moore and R.M. Hare that evaluative properties supervene on natural properties part of what makes this view plausible is that it would be evaluatively inconsistent to make differing evaluative judgements on two things that did not differ descriptively. Other supervenience claims do not so obviously turn on claims about the supervenient domain, but on further examination turn out to do so. To take a relevant example, functionalist approaches to the mental make plausible the supervenience of the mental on the physical, because functionalism has it that mental states are identified by their... 

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