Conscious experience is at once the most familiar thing in the world and the most mysterious. - David Chalmers

Why doesn't all this information-processing go on "in the dark", free of any inner feel? ...We know that conscious experience does arise when these functions are performed, but the very fact that it arises is the central mystery. There is an explanatory gap [a term due to J. Levine, "Materialism and qualia: The explanatory gap" Pacific Philosophical Quarterly 64:354-61, 1983] between the functions and experience, and we need an explanatory bridge to cross it.

The easy problems of consciousness are those that seem directly susceptible to the standard methods of cognitive science, whereby a phenomenon is explained in terms of computational or neural mechanisms. The hard problems are those that seem to resist those methods. ...The really hard problem of consciousness is the problem of experience. When we think and perceive, there is a whir of information-processing, but there is also a subjective aspect. ...When we see, for example, we experience visual sensations: the felt quality of redness, the experience of dark and light, the quality of depth in a visual field. Other experiences go along with perception in different modalities: the sound of a clarinet, the smell of mothballs. Then there are bodily sensations, from pains to orgasms; mental images that are conjured up internally; the felt quality of emotion, and the experience of a stream of conscious thought.

In developing my account of consciousness, I have tried to obey a number of constraints. The first and most important is to take consciousness seriously. The easiest way to develop a "theory" of consciousness is to deny its exis­tence, or to redefine the phenomenon in need of explanation as something it is not. This usually leads to an elegant theory, but the problem does not go away.