The hard problem of consciousness

Why does any physical process give rise to subjective experience? Even given a complete account of the brain's information processing, it is not clear why it should feel like anything. David Chalmers called this the 'hard problem' of consciousness.

Positions range from illusionism (experience is a kind of self-representation) to panpsychism (some form of experience is a fundamental property of matter). The problem resists both empirical and a priori resolution.