Now for most natural phenomena that need explaining, we get a physical explanation. To explain the gene, say, we get an explanation involving DNA. We discover how DNA and a bunch of complex molecules store information and transmit it from one generation to the next and then we say we've explained the gene - that's what Watson and Crick started to do and that research program has been pushed forward. In that sense we don't say we just have a correlation - "wow, where you have DNA you have a gene" - there you have an explanation. You've explained everything because all you have to do in explaining the gene is explain how hereditary characteristics get passed from one generation to the next. That's a problem about how functions get performed, and we solve that sort of problem by specifying mechanisms.

Same for all the easy problems I talked about. How is it that the brain discriminates information? How is it that we make reports? Those are questions about how the brain performs certain functions, how it does something. To solve that kind of problem what you need to do is specify a mechanism that performs the function, and then I think you've answered those questions. But what makes the hard problem different, almost unique, perhaps, is that it doesn't seem to be that kind of question. You can specify the mechanism, you can tell how all the functions in the vicinity are performed and there's still this further question: Why is it that that mechanism and the performance of those functions gives rise to experience? So, while one may have a correlation there, there doesn't seem to be explanation, precisely because what needs to be explained here isn't something about what the brain does but something, in a sense, about what the mind is.

So, given that the brain does give rise to subjective experience (and I believe it does, I think there's a very tight link there), it seems that there's something fundamental and primitive about that link. The way I put it sometimes is this: think about God creating the world, metaphorically. It seems that it is within God's powers, logically, when creating the world, to create creatures which are physically just like me, even have brains just like me, but have no subjective experience. That doesn't seem to me a conceptual contradiction. They are the famous philosopher's zombies.

Now, we aren't such zombies, we are in fact conscious beings. But the very fact that we are conscious beings indicates that there's something in us, over and above the basic physical components. Maybe there are some sort of basic mental components in there as well.

SJ: How can we move from correlation to explanation?

DC: We may have to recognise that there are just correlations between what's going on in the brain and what's going on in consciousness. But if we do that, we don't just want to stick with correlations like "okay, well when you get a brain like X you get a conscious state like Y". That would be a big tangle of messy correlations. I mean, in physics you may start with a bunch of correlations describing phenomena in mechanics or thermodynamics, and you can say well, when this gas goes into this state then it produces such and such behaviour, i.e. pressure and temperature work like this. But then you go for the underlying laws, the underlying principles that explain all this, and you go for the ultimate, the simple, fundamental principles of physics which underlie and explain all these high level correlations.