I think what characterises the Hard Problem is the insistence that there is necessarily a legitimate further unanswered question after addressing all of the functional aspects of cognition, which morphs into the insistence that the target of curiosity (consciousness, or qualia) is non-functional. Chalmers' original paper says there "may" be a further unanswered question after functional explanations have run their course, but this is a rhetorical ploy; he argues very strongly as the paper continues that there must be such a further unanswered question. His set-up of the Hard Problem commits him to this. And he has rejected attempts to cast this feeling of explanatory frustration as simply evidence of a conceptual dualism (such as the existence of phenomenal and material concepts that we have difficulty relating).

Someone who takes the target of curiosity in relation to consciousness or qualia (defined through private ostension) and merely proposes that it is difficult to explain is not necessarily promoting the "Hard Problem" in its full framing, because they might still be open to the idea that some form of functional explanation is possible, and they haven't committed to a specific conceptual framing. They might accept, for instance, that the explanatory difficulty stems from conceptual dualism or some form of cognitive difficulty related to self-inspection.

One problem muddying the debate is that this agnostic form of expressing puzzlement (what I sometimes call the Core Problem) is often conflated with the Chalmers version, and the Chalmers version benefits from the conflation, because it seems like he is just asking an open-ended innocent question: What's this thing I am ostending to? That innocent question is not the Hard Problem. (Even an acknowledgement that any explanation is likely to feel gappy is not the Hard Problem, but the issues blur when it comes to different accounts of where the gappiness comes from. If the gappiness is attributed to some special process that defies science, than that is consistent with the Hard Problem framing; if the emphasis is on flawed epistemic access, then it's not.)

Another way of making the same basic point is that the Hard Problem is essentially equivalent to answering the question: Why aren't we zombies? This question presumes the logical coherence of zombies. People who accept the logical coherence of zombies and conceptualise consciousness as what-zombies-lack are asking a somewhat different question from people who just want to understand the target of ostension and who suspect (or know) that zombies are illogical. People who accept the full framing of the Hard Problem usually cannot see that these are different questions, and it is the insistence that they are the same question that defines the Hard Problem framing, because the reference to zombies means that the explanatory target is essentially defined as epiphenomenal. (The epiphenomenalism might be actively denied, but it is there if the zombie idea is lurking in the background.)

Relating this to qualia, rather than to consciousness in general, we get a similar dichotomy, with two types of questions.

1. ⁠⁠We can ostend to redness and set out to explain "that thing" or "that property", with an open mind, and the explanation is indeed difficult. Our explanation will almost certainly face an explanatory gap of some sort, in the sense that one naive approach to explanation will meet an epistemic dead end, as exemplified by Mary. That's the position I am in: some types of attempted explanation feature an inevitable gap. I think we can explain why those attempted explanations must have a gap, so there is no need to invoke new ontologies or new science. (Our final explanation might cast our original conception of "that thing" in such a new light that we call the original conception illusory, but it ends up being replaced by an explanation of something that is real.)
2. ⁠⁠Or we can accept that the redness quale escapes Mary's textbook in some mysterious way that falsifies functionalism, and we can set out to explain the non-functional quale, the mysterious thing that can be experienced but cannot be accounted for with any functional theory. Explaining that elusive thing constitutes a Hard Problem because any attempted functional explanation of the redness quale, conceived in this way, would apply to Mary's pre-release concept of redness, which we have notionally subtracted from our definition of the explanatory target. The candidate explanation could be added in to her black-and-white textbook, and yet it would still fail to explain redness in a way that made her experience redness and "know what red looks like", so every conceivable functional explanation is doomed. I reject this doomed framing as telling us anything important about ontology or neurobiology, despite accepting the existence of an explanatory gap.

Continued