The Hard Question
David Chalmers, Professor of Philosophy at the University of California at Santa Cruz, calls this the "hard problem". The "easy problems" of consciousness are those concerned with brain function and how it relates to mental processes. We may, in years to come, unravel the workings of the brain sufficiently to be able to chart the complex neurophysiological processes behind perception. We may understand how we discriminate, categorize and react to stimuli; how current information is integrated with past experience; how we can focus the attention; how we can have an intention and deliberately control our behavior; and what distinguishes wakefulness from sleep and other unconscious states. To say these problems are "easy" is, of course, a relative assessment. It will take years of dedicated and difficult research, and we may follow many blind alleys in the process; nevertheless given sufficient time and effort it seems reasonable to believe that they will eventually yield to explanation.
The really hard problem is consciousness itself. Why should this complex processing of information lead to an inner experience? Why doesn't it all go on in the dark, without any subjective aspect? Why do we have any inner life at all?