After having been neglected for most of the twentieth century, the subject of consciousness has become fashionable. Amazon lists 3,865 books under “consciousness,” a number of them new releases of the last year or two. What exactly is the problem of consciousness, and why exactly is it so difficult, if not impossible, for us to agree on a solution to it? Of course, there is more than one problem, and there are many different reasons for disagreeing with proposed solutions. The hard problem of consciousness is to account for how it can exist and function in a way that is private, subjective, and qualitative, in a world that consists of public, objective, physical phenomena. How, for example, could the electrochemical activities of a kilogram and a half, about three pounds, of matter in my skull cause all of my conscious experiences? The problem of consciousness is the heart of the traditional “mind-body problem” in philosophy. What is the relation of the conscious mind to the physical brain and the rest of the body?
Before we can consider this question, we need at least a working definition of “consciousness.” Though we cannot yet give a scientifically precise, analytic definition of the word, it is not at all hard to give a common-sense definition that will help identify the issues that need to be addressed. It is important to do this because different writers use the word differently. By “consciousness,” I mean those states of sentience or feeling or awareness that begin when you wake up from a dreamless sleep and continue on throughout the day until you fall asleep again, or otherwise become unconscious. Dreams are also a form of consciousness.
Consciousness, so defined, has three remarkable characteristics. First, there is always a qualitative feel to our conscious experiences. Think of the difference between listening to music and tasting wine. Second, consciousness is always subjective in the sense that it only exists as experienced by human or animal subjects. It has a first-person mode of existence that requires some “I” that actually experiences the conscious states. And third, pathologies apart, each conscious state comes to us as part of a single, unified conscious field. So we don’t just have the taste of the wine and the sound of the music, but both of these are part of one large conscious experience. These three features are not independent. They are different aspects of the essential character of consciousness that can be accurately called qualitative subjectivity.
We can also briefly describe what we already know about conscious states and what we want a theory of consciousness to account for:
Consciousness is real and ineliminable. It cannot be dismissed as some kind of an illusion, or reduced to some other phenomenon. Why not? It cannot be shown to be an illusion because if I consciously have the illusion that I am conscious, I already am conscious. Consciousness exists subjectively, in the sense that it only occurs as experienced by a human or …