Propositional Attitudes and the Supervenience Strategy
Propositional Attitudes and the Supervenience Strategy
Another popular view, which has even been accepted by some Christians, is a nonreductive materialist position. On this view intentional states are not eliminated; they are not reducible to physical states. They are, however, supervenient upon physical states. Mental states are not identical to physical states, but given the state of the physical, there is only one way the mental can be.
Of course, earlier I indicated that supervenience of all nonphysical states on physical states is part of what is required for a worldview to be naturalistic. However, if mental states can be reductively analyzed in terms of physical states, then the supervenience is simply obvious. A difference in B requires a difference in A because, in the final analysis, Bs just are As. Again, if the B states are eliminated from the ontology, then we don't have to worry about a difference in B that is not guaranteed by a difference in A. However, for many, perhaps most, philosophers who believe in a broadly materialist worldview, the reductionist and eliminativist positions are both implausible. For these philosophers the supervenience relation has a job to do: it explains how it is possible for everything to be in the final analysis physical while at the same time maintaining the irreducibility and the autonomy of the mental realm.
Philosophers often distinguish between weak supervenience and strong supervenience. According to weak supervenience, B properties weakly supervene on A properties if and only if things that are alike in their A properties are always alike in their B properties. What this establishes is a constant conjunction between A properties and B properties. It does not really show that there is anything about the A properties that guarantees that the B properties will always be the same. Nevertheless, we must remember what caused problems for reductionist accounts of mental states. The physical is incurably indeterminate with respect to propositional states. Whatever story we tell at the physical level is compatible with a multiplicity of stories at the mental level. This kind of constant conjunction claim, however, explains little. There is, for example, a constant conjunction between increases in the homicide rate in New York City and increases in the rate of ice cream consumption. We could say that the homicide rate supervenes on the rate of ice cream consumption, but we will have explained nothing. We will not have shown that ice cream consumption is responsible for homicides, or vice versa, or whether these are just two unrelated effects of a common cause (an increase in the city's temperatures).16
A good deal of confusion in the discussion of neuroscientific discoveries and their relation to the philosophy of mind often occurs at this point. What neuroscience is often able to do is provide correlations between certain mental states and activity in certain parts of the brain. These are often taken as proof of materialism, but there is no good reason dualists should not expect these correlations to exist. Further, correlation between mental states and physical states is not the same as identification of mental states with physical states.
Strong supervenience is the claim that B properties strongly supervene on A properties just in case things that are alike in A properties must be alike in B properties. On this view the supervenience isn't just a brute conjunction; it is necessarily so. However, as an attempt to explain anything, this seems inadequate as well. Religious explanations are often taken to task as being God-of-the-gaps explanations; this just seems to be a necessity-of-the-gaps explanation.“Why, if Jones's beliefs could be five or six different ways given the physical, or perhaps, given the mental, Jones could be a zombie with no beliefs at all, does Jones have the beliefs he has?” If the answer is“Well, there's this strong supervenience relationship that exists between the physical and the mental, so it's necessary,” it looks as if we are taken no closer to an explanation as to why Jones has the beliefs he has.
Why does the supervenience relation exist, if it does? Is it pure dumb luck? Is it a Leibnizian preestablished harmony set up before the foundation of the world by God? (This might not be naturalistically acceptable.) Presumably, it is not a physical relation, so why does it exist? Unless something about the physical guarantees that the mental be only one way, the supervenience relation needs to be explained. There is what James Stump calls a“classic reflexivity problem” for the supervenience theorist. For supervenience theory everything is either physical or supervenes on the physical.17 So the supervenience relation is going to have to be either physical or supervene on the physical, if supervenient physicalism is true. But does it? Stump summarizes an argument originally presented by Lynch and Glasgow to contend that the supervenience relation itself cannot be admitted into the supervenient materialism's ontology, which I have altered slightly for the sake of congruence with previous discussion:
- They themselves could supervene on A-properties. But then there is an infinite regress problem, for now we have to explain this new supervenience relation, which in turn needs to be explained, and so on ad infinitum. So this is no good.
- Or, the S-facts could not just be further A-properties, that is, facts about the physical entity. But then these facts do not bridge the explanatory gap between the B-facts and the A-facts.18
Perhaps the supervenience theorist can simply accept the supervenience relation as an unexplained brute fact. However, as J. P. Moreland argues, this is also deeply problematic for the supervenience theorist: First, he highlights the claim made by supervenience theorist Terence Horgan that in a broadly materialist universe the truths of supervenience must be explainable rather than sui generis. As Horgan points out, if there are going to be any brute unexplainable givens in a materialist universe, it must be the physical facts themselves, not some fact concerning interlevel supervenience.19 Second, the truth of supervenience does not look like something science could possibly have discovered, and so to accept supervenience as a brute fact would be to accept the idea that truths about the world can be figured out by philosophical rather than scientific means, and this is anathema to most contemporary naturalists.20 Also, this position begs the question against people like Swinburne and Robert Adams, who maintain that the supervenience of the mind stands in need of a theistic explanation.21
Second, debate about just what kind of supervenience holds between physical and mental states is not a scientific question and cannot be settled by scientific theorizing. Further, supervenience theory involves terms and concepts that are not the terms and concepts of natural science. As Moreland puts it:
Naturalists criticize Cartesian dualism and its problem of interaction between radically different sorts of entities. In my view, the dualist has the resources to answer this problem because of her commitment to entities, relations, and causation that go beyond those in the physical sciences. But the same cannot be said for naturalism, and what is sauce for the goose is sauce for the gander. Naturalists have the very same kind of problem that they claim as a difficulty for the Cartesian. And given the philosophical constraints that follow from accepting the naturalist epistemology, etiology, and ontology, it is more difficult to see how a naturalist could accept mental/physical supervenience than it is to understand how a Cartesian without those constraints could accept mental/physical interaction.22
Intentionality is more than just a puzzle for naturalism; it is a deep and profound problem distinct from, and as serious as, the“hard problem” of consciousness. Reduction of understood intentional states and propositional intentional states seems to be inherently impossible. Elimination of those states eliminates states essential to the operation of the natural sciences on which the credibility of naturalism is founded. Nonpropositional successors to propositional attitudes cannot do the job assigned to them. Supervenient materialism commits the materialist to a materialistically unacceptable relation between the physical and the mental and, as we shall see, presents serious problems in accounting for mental causation.
Theories of the universe that make the mental a basic fact of reality, such as theism, pantheism, or idealism, do not have the problem of unacceptably terminating explanatory chains with mental states. If the mental is part of the basic furniture of the universe, then it seems a good deal easier to see how it could end up being instantiated in human beings.