 The Conceivability argument (Chalmers 1996, 2003) has it that “zombies” are conceivable—physical duplicates of ordinary human beings, that share all the human physical and functional states but lack phenomenal consciousness in sense (4); there is nothing it is like to be a zombie. The argument then moves from bare conceivability to genuine metaphysical possibility, which would refute materialism. According to the Explanatory Gap argument (Levine 1983, 2001), no amount of physical, functional or other objective information could explain why a given sensory state feels to its subject in the way it does, and the best explanation of this in turn is that the feel is an extra fact that does not supervene on the physical.