The explanatory gap has vexed and intrigued philosophers and AI researchers alike for decades and caused considerable debate.
Ned Block argues that there also exists a "harder problem" of consciousness, due to the possibility of different physical and functional neurological systems potentially having phenomenal overlap.
[4] In contrast, it is thought by many mind-body dualists (e.g. René Descartes, David Chalmers) that subjective conscious experience constitutes a separate effect that demands another cause that is either outside the physical world (dualism) or due to an as yet unknown physical phenomenon (see for instance quantum mind, indirect realism).
Proponents of dualism claim that the mind is substantially and qualitatively different from the brain and that the existence of something metaphysically extra-physical is required to "fill the gap".
In addition to the qualities of subjective experiences, the existence of personal identity also poses potential problems for physicalist philosophies.
[9] Joseph Levine[clarification needed] and others opt to either remain silent on the matter or argue that no such metaphysical conclusion should be drawn.
[10]However, such an epistemological or explanatory problem might indicate an underlying metaphysical issue—the non-physicality of qualia, even if not proven by conceivability arguments, is far from ruled out.
[11] Levine points out that understanding how much there is to be known about qualitative experience seems even more difficult because we lack a way to articulate what it means for actualities to be knowable in the manner that he has in mind.
[clarification needed] Levine argues that it seems counterintuitive to accept this implication that the human brain, so highly organized as it is, could be no more than a routine executor.
][citation needed] Christian List believes that the existence of first-personal facts provide a refutation of not only physicalist theories of consciousness, but also most standard versions of dualism.