Philosopher Russell Blackford at New Philosopher gives us an example of this response. When he speaks below of the "explanatory gap" he's talking about the vast gulf that lies between physical phenomena like the firing of neurons and mental phenomena like the experience of the color red. At the present there's simply no explanation for how we get from one to the other.
Some contemporary philosophers who make much of the explanatory gap, including Levine, Galen Strawson, and, perhaps most famously, David Chalmers, are broadly sympathetic to ideas of philosophical naturalism.Of course there's no reason to accept Levine's hypothesis other than an apriori metaphysical commitment to materialism. Blackford goes on to discuss the problem with Levine's view:
Indeed, Levine puts forward a strong argument for a strictly materialist approach to mind in which conscious experiences somehow just are physical processes. His argument assumes that the physical causal order is closed and that our conscious experiences are causally efficacious, not mere by-products of our physical functioning like smoke from a fire. If we accept both of these apparently plausible assumptions, it follows that our conscious experiences are themselves physical phenomena.
It is hard to define a sense in which conscious experiences are identical to physical phenomena such as neurological processes, but without any further twists that in itself might be a solvable conceptual problem. But there’s a further twist. As Levine also brings out in his discussion, physics as we currently understand it ultimately does no more than describe physical entities, structures, etc., and their dynamics. Understood in this way, a complete and ideal physics could account for all the motions and transformations of matter and energy that take place.Is there a solution to the problem posed by qualia (and several other phenomena such as intentionality, restricted access, et al.)? Well, no, but maybe there will be in the future:
Indeed, it would account all the way up from the base level for the emergence and evolution of life, neurophysiological structures and processes, our bodily movements, and even for the things that we say to each other. The emergence of all these would ultimately be predicted by descriptions of physical structures together with the laws that describe their motions and transformations.
However, nothing in an ideal physics, so conceived, would enable us to deduce that human beings have inner experiences such as when I have an appearance of redness in my visual field, or a feeling of warmth and softness to my touch when I stroke my cat’s fur.
The emergence of such qualitative features of the world, or “qualia”, could not be predicted by a physical theory that merely specified physical structures and the laws governing their dynamics. When it comes to our conscious inner experiences, there seems to be a gap between the ultimate – or “lowest level” – physical description of reality and features of the world involving consciousness.
If we accept that this is a genuine problem, how do we solve it? Presumably we will need to enrich our fundamental world picture in some way. This could be done if our basic laws of physics were supplemented by psychophysical bridge principles that physical structures and processes generate the phenomena of consciousness.This is a bit odd. Blackford places his hope in difficult to discover bridge principles which could exist but for which there's no evidence. Yet as a materialist he's loath to consider that minds could exist - though they'd be difficult to discover - even though there's lots of evidence for them. Couldn't one say with Blackford, "I don't see why they couldn't exist"?
Such bridge principles might be very difficult for limited beings like us to discover, but I don’t see why they couldn’t exist.
If we knew what [these bridge principles] were, we could give an explanation as to why some highly complex structures – such as the human brain – are conscious, while other structures are not. There might still be problems, however, in avoiding epiphenomenalism (the view that mind arises from the brain but cannot affect the brain). Would the new, enriched theory allow consciousness, in its turn, to act upon the physical world, as certainly seems to happen?The problem seems intractable given materialism. Of course, dualists of one stripe or another, though not without difficulties of their own, nevertheless argue that the reality of consciousness implies that materialism is inadequate. The existence of consciousness suggests that in addition to our physical brains there's also something else about us, an immaterial substance (mind), that mediates conscious experience. Some philosophers have sought to solve the problem by simply denying that consciousness is a genuine reality, but Blackford will not have any of that nonsense:
Or might we bite the bullet of epiphenomenalism once and for all, treating the apparent causal efficacy of consciousness as an illusion?
Nonetheless, our own conscious experience cannot simply be waved away; in fact nothing is more real to us. Furthermore, it does seem difficult to understand its place in the order of the physical universe without some breakthrough in our understanding of physics itself. The explanatory gap identified by philosophers has to be explained, or explained away, if we want a satisfying account of the relationship between the physical world and our own inner lives.Perhaps what he meant by that last sentence is "if we want a satisfying materialistic account...," but why should we insist that any account of reality be materialistic?