Tom Nagel has an interesting engagement, or tussle, with empirical fact in his recent book, Mind and Cosmos. He writes:
With regard to evolution, the process of natural selection cannot account for the actual history [of consciousness] without an adequate supply of viable mutations, and I believe it remain an open question whether this could have been provided in geological time merely as a result of chemical accident, without the operation of some other factors determining and restricting the forms of genetic variation.
This is startling. Is it really in the purview of a philosopher to assert, and on an extremely flimsy scientific foundation, that the supply of mutations is insufficient to produce consciousness? Or even that it is an open question? (Keep in mind that Nagel’s judgement is not based on an expert review of the literature. He cites Michael Behe and Stuart Kauffman, as well as “the untutored reaction of incredulity to neo-Darwinism.”) On this slight basis, Nagel makes a case for teleologically directed mutation, once again an apparent excursus into scientific theorizing.
When is it legitimate for philosophers to get embroiled in empirical matters?
Again, there are facts on which philosophical theories depend. For instance, philosophers “discovered” opponent processing and colour constancy in the middle nineteen-eighties, and this marked the end of earlier theories based on the assumption that perceived colour corresponded to retinal irradiation.
Let’s save these sorts of empirical embroilments for another day. They are cases where philosophical theories turn on empirical facts, or philosophical facts on empirical investigation.
Nagel’s charge into biology is much more perilous. It is a philosopher pronouncing on empirical facts and building a scientific theory (or the basis for such a theory) on the back of these facts. Whether you find his theory foolhardy or exhilarating will depend on your philosophical proclivities.
Now here is a more complex example. As I discussed last week, a very big deal has grown up around mind-brain identity theory. Materialist philosophers of mind are inclined to hold that every mental event is completley materially determined by physical reality. There is no mental fact that does not arise from a material basis.
The argument against this is grounded in the metaphysics of modality.
It is metaphysically possible that molecule-by-molecule duplicates of human beings completely lack consciousness.
Therefore, consciousness in the actual world is not materially determined. It is something extra to its molecule-by-molecule structure.
Suppose that this argument is sound. (It has a good deal of plausibility, I think.) It seems to sink materialism. But, to bring things home to our present discussion of empirical embroilment, what does it do to present-day neurophysiology? Can philosophy sink the latter?
Here is the difficulty. Neurophysiology is thought to support material determination of consciousness. The evidence is that various neural events seem to coincide with various conscious events. On the other hand, metaphysical evidence tells against determination. Suppressing doubts and worries about how exactly we should formalize the opposition between the two, we seem here to have a case where empirical science and philosophy point in opposite directions about an empirical matter. But is this really possible? How can metaphysical possibility tell against scientific theories based on empirical investigation—about empirical matters?
My puzzlement is only deepened by philosophical theories that try to account for consciousness in non-physical ways. David Chalmers (“Consciousness and Its Place in Nature”) has expressed a tentative sympathy for Russell’s neutral monism. Russell pointed out that the basic physical entities were defined relationally and dispositionally. Yet, dispositions must have a basis in intrinsic properties. But: “Physics is silent about the intrinsic nature of a quark, or about the intrinsic properties that play the role associated with mass.” Pointing out that phenomenal properties are intrinsic, Chalmers asks whether it would not make sense to say that the basic entities of physics are constituted by phenomenal properties, that phenomenal or “proto-phenomenal” properties might be the constitutive basis of both matter and mind. And this seems, on the face of it, to be a foray into physics. How can a priori theorizing support a theory of physics?
As I said last week, I think the problem arises from what I called “strong modals”—modal propositions the truth conditions of which totally transcend evidence available in the actual world. (Well, conceivability is actual world evidence that is taken to tell us about distant possible worlds. So I suppose I should say: "non-intentional evidence.") Science tells us about causal determination in the actual world. This has immediate implications about the structure of nearby possible worlds. Metaphysics, on the other hand, uses strong modals as evidence from very distant worlds to oppose what science seems to tell us about the actual world.
Identity is a strong modal in this sense. Perhaps “determines” is as well, as it occurs in “consciousness is materially determined.” If you think there is something odd about metaphysics opposing science, perhaps you should worry about strong modals opposing scientific propositions. The question is: How can they when the evidence for the two is disjoint. So perhaps there is an illusion at work. Since science cannot tell us much about strong modals, perhaps we should accept that strong modals cannot tell us about science.
This, of course, raises two large problems. First, and perhaps this is just a technicality: If science doesn’t tell us about metaphysical determination, and only about nearby worlds, how shall we formulate what science tells us. And second, if metaphysical determination is compatible with everything that science tells us, but only reveals something about very distant worlds . . . Well, of what interest is it?