The Hard Problem in Chalmers' Own Words

“Even if we solved all the 'easy' problems, explaining discrimination, integration, access consciousness, attention, there would still remain a further problem: why does all this processing give rise to conscious experience? Why is there something it is like to undergo these processes? This is the ==hard problem== of consciousness. [...] It is perfectly conceivable that all these cognitive and behavioral functions could have been performed in the absence of experience. The ==hard problem== is precisely the problem of explaining why they are not. Nagel's formulation: the subjective character of experience, the fact that there is something it is like to be an organism, cannot be fully captured by any objective account. The reduction of mind to brain, even if complete at the functional level, leaves something unexplained. — Chalmers, 'Facing Up to the Problem of Consciousness' (1995); Nagel, 'What Is It Like to Be a Bat?' (1974); SEP 'Consciousness'”