The subject matter is perhaps best characterized as “the subjective quality of experience.” When we perceive, think, and act, there is a whir of causation and information processing, but this processing does not usually go on in the dark. There is also an internal aspect; there is something it feels like to be a cognitive agent. This internal aspect is conscious experience. Conscious experiences range from vivid color sensations to experiences of the faintest background aromas; from hard-edged pains to the elusive experience of thoughts on the tip of one’s tongue; from mundane sounds and smells to the encompassing grandeur of musical experience; from the triviality of a nagging itch to the weight of a deep existential angst; from the specificity of the taste of peppermint to the generality of one’s experience of selfhood. All these have a distinct experienced quality. All are prominent parts of the inner life of the mind. We can say that a being is conscious if there is something it is like to be that being, to use a phrase made famous by Thomas Nagel.
Chalmers is best known for his formulation of the notion of a hard problem of consciousness in both his 1996 book and in the 1995 paper “Facing Up to the Problem of Consciousness”. He makes a distinction between “easy” problems of consciousness, such as explaining object discrimination or verbal reports, and the single hard problem, which could be stated “why does the feeling which accompanies awareness of sensory information exist at all?” The essential difference between the (cognitive) easy problems and the (phenomenal) hard problem is that the former are at least theoretically answerable via the standard strategy in philosophy of mind: functionalism. Chalmers argues for an “explanatory gap” from the objective to the subjective, and criticizes physical explanations of mental experience, making him a dualist. Chalmers characterizes his view as “naturalistic dualism”: naturalistic because he believes mental states are causedby physical systems (such as brains); dualist because he believes mental states are ontologically distinct from and not reducible to physical systems.
Actually, I think my view is compatible with much of the work going on now in neuroscience and psychology, where people are studying the relationship of consciousness to neural and cognitive processes without really trying to reduce it to those processes.