Again, Supervenience

Again, Supervenience

There is a well-known problem with physicalism: the problem of defining it. Briefly: do we mean the mind is reducible to the brain as now understood, or do we mean the mind is reducible to the brain as it may be understood in the future? Do we mean current actual neuroscience or do we mean a future possible neuroscience? The former seems too restrictive and the latter too open-ended. I am not going to go over this problem now; my aim is to extend the argument to supervenience claims. The mind is held to supervene on physical properties of the body and brain, but what is meant by “physical” here? The dilemma is that this will either be too restrictive or too liberal, and hence either false or empty. Is there any version of the claim that can escape this dilemma? Suppose supervenience were propounded two hundred years ago when very little was known about the brain, specifically the nerve impulse; perhaps only the brain’s gross anatomy was known. Is the mind supervenient on that? Clearly not, because a completely insensate object could share that gross anatomy (e.g., a plastic model of a brain). The details of neurons and neural impulses matter. And it would be premature to suppose that nothing further will be discovered as to the brain’s neural properties. We should not limit the supervenience base to what we currently know of the brain. But then we are left with a lack of clarity about what the “physical” supervenience base consists in.

There are subsidiary questions. Is anything about the mind supervenient on what we now know of the brain? That does not seem out of the question: perhaps dispositional properties of mental states are so supervenient, or some structural and temporal properties. Not qualitative intrinsic properties but behavioral ones: maybe these depend wholly on neural impulses as we now understand them. The mind isn’t then wholly physically supervenient in this sense but it is partially so supervenient. Or perhaps not. The question is more empirical than a priori. Next: Is the mental supervenient on a subset of the brain’s properties not all of them? That is surely very plausible: some properties will be irrelevant to the mind, e.g., the color of the brain or its particular shape or whether it tastes good with spinach. It would be nice to know which of the known properties of the brain form the supervenience base. The bare assertion that the mind depends on the brain is unilluminating because much too coarse—we want to know which physical properties are crucial. We know that some parts of the brain have no mental correlate (e.g., the brain stem), so what is it that makes other parts of the brain capable of generating the mind? What is the physical difference? It can’t be the presence of the neural impulse, because that does not always lead to a mental correlate. Supervenience alone tells us almost nothing of interest; and it is either false or an empty truism. What we need is a theory that specifies precisely what aspects of the brain form the supervenience base. The muscles are supervenient on the body—yes, but what aspects of the body? If we knew the answer to that, we would be close to explaining the supervenience; but then, we wouldn’t be limited to a bare supervenience claim. Such a claim is next to useless unless it permits of conversion to an explanatory theory, but then it isn’t necessary. In short, brute supervenience is a pointless idea—an empty slogan. It should be banned.

Suppose we held that mental properties are physical properties of the brain, in some workable sense of “physical”. Then, trivially, mental properties would be supervenient on physical brain properties. That would be a doctrine of zero interest. No, we must mean by “physical” non-mental. So, the claim must be that the mental is supervenient on the non-mental. Do we really want to say that? We must rigorously exclude any hint of the mental from the putative non-mental supervenience base (so panpsychist properties must be excluded). This would mean the supervenience base would have to be compatible with the absence of the mental—but that contradicts supervenience! For example, if electrical properties were held to constitute the supervenience base, we would face the objection that electricity doesn’t entail mentality, which contradicts supervenience. But electricity is exactly what the brain traffics in, so it can’t be sufficient. How can the mental supervene on the non-mental, i.e., that which doesn’t require a mental correlate? If, however, the mental supervenes on some sort of proto-mental or quasi-mental base, then we don’t have supervenience on the non-mental. Either way psychophysical supervenience doesn’t work. Perhaps we can identify some properties of mental states that supervene on electro-chemical properties of the brain, such as dispositional-behavioral properties; but that is not to say that any perfectly general supervenience claim can be intelligibly formulated. Supervenience on what is known of the brain seems to be either relatively trivial or false. It is really a foggy magical idea captured in a fancy word. All we have is the idea that the mind might be semi-supervenient on the properties of the brain currently recognized (and as currently recognized). For there is really no content to the claim that the mind (as a whole) is supervenient on the physical properties of the brain (present or future). It is certainly not the case that mentality supervenes on electricity and chemistry, or else mentality would be everywhere. As the term “physical” is understood now, it is clearly false that the mind is supervenient on the physical; and no other sense can be plausibly stipulated.[1]

[1] The fact is that physical supervenience inherits all the disadvantages of physicalism in respect of definition but none of the advantages in respect of ontology. It doesn’t tell us the nature of the mental and how it exists in the brain, and it makes no progress with saying what physicalist doctrines amount to. So, why has it been such a popular idea? Because it papers over the difficulties. The analogous doctrine in ethics tells us nothing about the nature of the ethical and also faces the problem of saying what precisely the supervenience base is to include and exclude (what exactly is a “descriptive” property?).