Esse est percipi, to be is to be perceived, said good old Berkeley; but, according to most philosophers, he was wrong. Yet, obviously, there are things for which the adage holds. Perception, trivially, to begin with. If elements of conscious awareness—pains, tickles, feelings of heat and cold, sensory qualia of colors, sounds, and the like—have any existence, it must consist in their being perceived by a subject.... This shows, of course, that such experiences are epiphenomenal, at least with respect to the physical world.