And this is a follow-up post I did afterwards.
I must admit that Lewis's "it is obvious" response made the issue seem like more of a slam dunk than I would think of it as being. This chapter was written before he encountered Anscombe, when he had underestimated the complexity of the argument, but Lewis just revised one chapter of the book in response to Anscombe, not all of it.
Of course thought is solidly based in the body, but can a complete description of the state of one's body thereby account for what one's thought is about? If we had all the physical facts, would any mental facts follow logically? It isn't just religious people who say that physicalists have problems accounting for the mind. For example's here's naturalist Ned Block:
We gain some perspective on the explanatory gap if we contrast the issue of the physical/functional basis of consciousness with the issue of the physical/functional basis of thought. In the case of thought, we do have some theoretical proposals about what thought is, or at least what human thought is, in scientific terms. Cognitive scientists have had some success in explaining some features of our thought processes in terms of the notions of representation and computation. There are many disagreements among cognitive scientists: especially notable is the disagreement between connectionists and classical "language of thought" theorists. However, the fact is that in the case of thought, we actually have more than one substantive research program and their proponents are busy fighting it out, comparing which research program handles which phenomena best. But in the case of consciousness, we have nothing--zilch--worthy of being called a research program, nor are there any substantive proposals about how to go about starting one. Researchers are stumped. There have been many tantalizing discoveries recently about neuropsychological syndromes in which consciousness seems to be in some way missing or defective, but no one has yet come up with a theoretical perspective that uses these data to narrow the explanatory gap, even a little bit.
Ned Block, ‘Consciousness’, in A Companion to Philosophy of Mind, (ed.) Samuel Guttenplan, (Blackwell, 1994), p. 211.
Or try that infamous Christian apologist Richard Dawkins
Neither Steven Pinker nor I can explain human subjective consciousness... In How the Mind Works Steven elegantly sets out the problem of subjective consciousness, and asks where it comes from and what’s the explanation. Then he’s honest enough to say, ‘Beats the heck out of me.’ That is an honest thing to say, and I echo it. We don’t know. We don’t understand it.
Richard Dawkins, quoted by Varghese, The Wonder of the World, p. 56.
Or how about that raving religious lunatic Susan Blackmore:
How can objective things like brain cells produce subjective experiences like the feeling that ‘I’ am striding through the grass? This gap is what David Chalmers calls ‘the hard problem.’ ...It is a modern version of the ancient mind/body problem – but it seems to get worse, not better, the more we learn about the brain... The objective world out there, and the subjective experiences in here, seem to be totally different kinds of things. Asking how one produces the other seems to be nonsense. The intractability of this problem suggests to me that we are making a fundamental mistake in the way we think about consciousness – perhaps right at the very beginning.
Susan Blackmore, ‘What is consciousness?’, Big Questions in Science, in Harriet Swain (ed.), Big Questions in Science, (Jonathan Cape, 2002), p. 29-40.
Now I am not saying these people are anywhere near arguing that the mind is supernatural. Far from it. But what I am suggesting is that the "facts" do not prove the the mind is physical, and that there should be no mystery about it, and that of course we all know that it is true. Rather, the conviction that the mind must be physical is one that is "read in" to the scientific data based on prior convictions about what people think must be true about nature.
And no, Lewis doesn't give you numbered premise arguments. I know of one guy, though, who wrote a book pulling enough numbered premise arguments out of Lewis to choke a horse. I forget his name. I'm not saying you need the numbers necessarily, but I thought asking for numbered premises might be useful in understanding the argument from evil, and so I asked for them. I've found numbered premise arguments a useful tool, but that is it.
Of course, Lewis and others such as myself have detailed arguments for why the mental states are not natural phenomena. To say that the facts prove that it is a natural phenomena is to provide a proof surrogate, not a proof.
What I was trying to do was show how Lewis perceived scientific thought: the right tool for many types of inquiry but nevertheless a "truncated" way to come up with a complete philosophy. Russell thought otherwise. He said "What science cannot discover, mankind cannot know." (I wonder what scientific discovery he based that off of? Unless he wasn't pretending to know it).