 Chalmers's version of the argument (1996a, 2002), known as the “Zombie Argument”, has been particularly influential. The first premise of this argument is that it is conceivable, in a special, robust, “positive” sense, that there are molecule-for-molecule duplicates of oneself with no qualia (call them “zombies”, following Chalmers 1996a). The second premise is that scenarios that are “positively” conceivable in this way represent real, metaphysical, possibilities. Thus, he concludes, zombies are possible, and functionalism — or, more broadly, physicalism — is false. The force of the Zombie Argument is due in large part to the way Chalmers defends its two premises; he provides a detailed account of just what is required for zombies to be conceivable, and also an argument as to why the conceivability of zombies entails their possibility (see also Chalmers 2002, 2006, 2010, Ch. 6, and Chalmers and Jackson 2002). This account, based on a more comprehensive theory of how we can evaluate claims about possibility and necessity known as “two-dimensional semantics”, reflects an increasingly popular way of thinking about these matters, but remains controversial. (For alternative ways of explaining conceivability, see Kripke (1986), Hart (1988); for criticism of the argument from two-dimensional semantics, see Yablo 2000, 2002, Bealer 2002, Stalnaker 2002, Soames 2004, Byrne and Prior 2006; but see also Chalmers 2006.)