Global Supervenience and Physicalism

One class of facts supervene on another if the former couldn't differ without a change in the latter. I've previously talked about this a lot in connection with morality, for instance: you couldn't have a world that was identical to our own in all respects except that Hitler was a good person. Because the moral facts supervene on the non-moral, the only way to change the former would be also to change the latter. (If Hitler had stayed out of politics and instead become a harmless hermit, then perhaps he would not have been so evil.)

Now, it seems to me that mostly all facts supervene on the physical. (The main exceptions being facts about phenomenal consciousness, and anything else which in turn supervenes upon those.) Indeed, this seems kind of obvious. But sometimes people object to such claims by adopting an overly restrictive view of the physical. For example, they might consider two objects which share all their intrinsic physical properties and yet differ in the supposedly supervening property X. But that merely demonstrates a failure of "local supervenience". X doesn't supervene on this restricted cluster of "local" physical facts. But that does nothing to refute the claim that X supervenes on the totality of physical facts. You can't just ignore all the relational physical properties and pretend you have a counterexample. Not that some people don't try.

A recent example is provided by the Maverick Philosopher, who writes:

But the reference is indeterminate if we go by the physical properties of the representations alone. Suppose I hand you two drawings of your mother, one an exact copy of the other, but you do not know which is the orig[i]nal and which is the copy. You cannot, by inspection of these drawings, tell which is which. Thus you cannot determine the reference from the physical properties.

But you cannot, by inspection alone, tell all of the physical properties of the drawings. You cannot tell, for instance, at what time each was drawn. But that's clearly a physical fact about the drawings. And clearly if someone knew all the physical facts, in this appropriately broad sense, they would no longer have any difficulty determining which drawing was the copy.

So BV has done nothing at all to show "that materialism doesn't work" (where "materialism" is synonymous with "physicalism", i.e. the claim that all facts supervene on the physical facts). He's shown that intentionality doesn't locally supervene on some restricted class of physical facts. But that shouldn't be surprising. Of course if we overlook some physical facts, then we won't be able to derive some other truths (say, about what a drawing refers to). That's because you're ignoring some crucial facts! The appropriate response is to open your eyes, not reject physicalism. (Actually, I think we should reject physicalism for other reasons. But this sorry argument surely isn't one of them.)

This confusion can also arise in discussions of scientific reductionism, and whether the biological supervenes on the physical. You couldn't have a world physically identical to our own in all respects, but somehow biologically different. There couldn't be any differences in species, for example, or in which organisms are living or dead, without some physical difference in the world. One might suggest that biological kinds aren't determined by the laws of physics alone; they also depend on physical history. But of course physical history is included in the class of physical facts, so we never should have excluded that in the first place. The thing to consider here is the entire 4-dimensional space-time "loaf" (encompassing past, present, and future), not just little bits of it.

Incidentally, this is a nice chance to talk about misusing the "vitalism" analogy. Recall our past discussion of how Kripkean examples of conceivable impossibities (e.g. Hesperus' being non-identical to Phosphorus) do nothing to support the impossibility of zombies. Another bad analogy often invoked in defence of materialism is that of vitalism: "People used to think that being alive was something beyond the physical, but science later proved them wrong. Why think consciousness is any different?"

But 'life' can clearly be analysed in functional and structural terms. There is no sense to be given to the notion of something that is functionally and structurally indiscernible from a duck, having all the same kinds of relations to other objects as another duck does, and yet somehow fails to really be a living duck. To be a living duck just is to have the right kinds of functional relations and so forth. There's nothing more to it than that. Not even vitalists disagreed, as Chalmers explains:

Vitalists typically accepted, implicitly or explicitly, that the biological functions in question were what needed explaining. Their vitalism arose because they thought that the functions (adaptation, growth, reproduction, and so on) would not be physically explained. So this is quite different from the case of consciousness. The disanalogy is very clear in the case of Broad. Broad was a vitalist about life, holding that the functions would require a non-mechanical explanation. But at the same time, he held that in the case of life, unlike the case of consciousness, the only evidence we have for the phenomenon is behavioral, and that "being alive" means exhibiting certain sorts of behavior. Other vitalists were less explicit, but very few of them held that something more than the functions needed explaining (except consciousness itself, in some cases). If a vitalist had held this, the obvious reply would have been that there is no reason to believe in such an explanandum. So there is no analogy here.

Now, we do indeed have every reason to believe that physical science can provide adequate functional explanations. But consciousness is different in that it cannot be analysed in functional terms. That's what zombies show us, for example: we can imagine creatures functionally indiscernable from ourselves, that nevertheless lacks conscious experience. Whatever consciousness is, it isn't just the having of certain functional relations. That's not what we mean by the term - our phenomenal concepts are something quite different.

One might more plausibly hold that our brain states "give rise to" our conscious states. But this is already to recognize that they are two different things, even if a (natural) lawful connection holds between them. The natural laws might have been different, after all. And in that case there might have been the same physical stuff but without giving rise to any phenomenal stuff. So that's why the phenomenal isn't reducible to the physical. (At most it supervenes nomologically, not metaphysically.)

Categories:

• metaphysics
• reductionism
• mind
• consciousness