“Facing Up to the Problem of Consciousness” is a 1995 paper by David Chalmers, published in the Journal of Consciousness Studies (volume 2, issue 3, pages 200 to 219) and self-archived on his website. It is the paper that introduced the now-standard phrase “the hard problem of consciousness.”
Chalmers separates the study of mind into two kinds of question. The easy problems are functional: how does a brain integrate information, focus attention, report on its internal states, distinguish one stimulus from another. He calls these easy not because they are simple but because we understand what shape a solution takes - you find the mechanism that performs the function. The hard problem is why all that functioning is accompanied by subjective experience: “Why is it that when our cognitive systems engage in visual and auditory information-processing, we have visual or auditory experience?” Even a complete mechanistic story, he argues, seems logically compatible with there being no experience at all - no “what it is like” to be the system.
The paper’s force is in showing that the usual methods of cognitive science, however successful on the easy problems, do not obviously touch the hard one, because explaining a function never seems to explain why the function feels like anything. Chalmers proposes taking experience as a fundamental feature of the world to be related to physical processes by bridging principles, rather than expecting it to be reduced away.
For debates about artificial intelligence, the paper draws the sharpest available line: every test we can run on a machine - its behavior, its self-reports, its problem-solving - bears on the easy problems, while the question of whether the machine has any inner experience is precisely the hard problem the paper isolates and which no such test can settle.