A well-known argument, due to Frank Jackson, goes as follows. (You can read the short version here.) The brilliant genius Mary has complete knowledge of physical reality. All the sciences, physics, chemistry, neuroscience, etc., have been completed—there is nothing more to add—so that the fundamental physical constituents and causes of all phenomena are known, together with everything that supervenes on them, and Mary has mastered all of this. But although Mary thus knows everything about the physical world there is to know, she does not know everything there is to know. For, a peculiarity about Mary is that she has lived her entire life in a black and white room and has never been permitted to view anything except in black and white. Thus, on the day when she finally leaves her room and sees, say, a red object, she will learn something she didn’t know before. She will say, “Ha! So that is what seeing red is like.” If this is correct, then, apparently, red, or the experience of seeing red, is not part of physical reality.

The “Mary” argument is just one of several ways to bring out what is really an old, classic problem with any sort of reductionistic physicalism. It is this. Continue reading →