I'd been thinking of writing a post on the subject – and maybe I will. But now I want to post bits of a post written by Keith Frankish. His 2nd and 3rd paragraphs:
Here’s one: rainbows. Rainbows are real, aren’t they? You can see them with your own eyes — though you have to be in the right position, with the sun behind you. You can point them out to other people — provided they take up a similar position to you. Heck, you can even photograph them.
But what exactly is it that’s real? It seems as if there’s an actual gauzy, multi-coloured arc stretching across the sky and curving down to meet the ground at a point to which you could walk. Our ancestors may have thought rainbows were like that. We know better, of course. There’s no real coloured arc up there. Nor are there any specific physical features arranged arcwise — the rainbow’s “atmospheric correlates”, as it were. There are just water droplets evenly distributed throughout the air and reflecting sunlight in such a way that from your vantage point there appears to be a multi-coloured arc.
That's it, really. An analogy to be sure, but a good one.
When I reflect on my own experience, it seems to me that my consciousness is an inner world, where the world around me is rendered in private mental qualities — “qualia” — for my benefit alone. But there isn’t such a world. Neuroscience finds nothing like it in the brain, nor even anything isomorphic to it. Rather, it finds complex trains of neural activity proceeding in parallel and triggering a host of reactions — physiological, psychological, and behavioural. My sense of having a rich qualia-filled inner world is an impression created by all these processes, but the processes themselves are as different from the supposed inner world as a moisture-infused mass of air is from a colourful aerial arc.
That is, it's like rainbows. Perfectly real, but not in the most obvious way.
It's like, when Chalmers posited the "hard problem" he asks us to imagine a complex circuit diagram that accounts for everything neuroscience has to say about consciousness. That's the "easy problem," solved!
Now, he asks, see consciousness anywhere in that diagram?
No, we reply.
That's the hard problem, and draws another box in the diagram. Find that box, and you've solved the hard problem, says he.
No. That's just make-work for philosophers, like digging ditches and then filling them back in.