Sometimes I tell people that science has nothing useful to say about consciousness. And they say: "What do you mean? We know a lot about the brain. Presumably consciousness is coming from there."
And I say something like: "Well, I'm not talking about the stuff that's explainable by the brain. I understand why I do the things I do in terms of the brain. I even understand why I discuss things like consciousness -- sort of -- in terms of the brain. But none of that necessitates actual subjective experience."
And then they don't seem to know what I mean..
This is where words like qualia come in, and nobody seems to agree about exactly what is being discussed..
But I think that lack of agreement is the essential defining characteristic of consciousness -- it is the aspect of our subjective experience which cannot be explained in words, not even words like qualia. Note that this definition says what consciousness is not, but not what it is. Anything that we say in an attempt to explain the true essence of subjective experience is, by the very fact that we are saying it, not subjective. It would presumably be possible to inspect someone's brain and see that they said the things they said because of the laws of the universe, without any need for true subjective experience.
The deep and strange philosophical claim that a conscious entity makes by asserting that it is conscious is that there is something about itself that it cannot explain in words -- or any other way -- and cannot prove exists.