 Those who exploited the zombie idea in the 1970s typically assumed without argument that zombies are not just conceivable but possible (e. g. Campbell 1970, Nagel 1970). When Chalmers reactivated the idea, he found the conceivability of zombies ‘obvious’, remarking that ‘it certainly seems that a coherent situation is described; I can discern no contradiction in the description’ (1996, p. 96). However, he also recognized that this intuition cannot be relied on. The nature of conscious experience is after all hard to understand: what strikes some people as obviously possible could still turn out to harbour hidden contradictions (Nagel 1998; Stoljar 2001). Clearly, those who maintain that zombies are conceivable must provide justification, recognizing that, being an epistemic claim dependent on our cognitive abilities, it is defeasible.