 Kirk (1974a, 1974b) attempted to provide such justification, in the form of arguments intended to show that zombies are possible (hence conceivable). However, they fall well short of their target, depending on much the same cluster of intuitions as the original idea. Chalmers (1996) presented a series of five arguments against the view that there is an a priori entailment from physical facts to mental facts. Each argument would directly or indirectly reinforce the intuitive appeal of the zombie idea. The first will be considered shortly; the other four appeal respectively to the alleged possibility of ‘inverted spectrum’ without physical difference (see inverted qualia); the alleged impossibility of learning about conscious experience on the basis of purely physical information; Jackson’s (1982) ‘knowledge argument’ (related to the last); and what Chalmers calls ‘the absence of analysis’: the point being that his opponents ‘will have to give us some idea of how the existence of consciousness might be entailed by the physical facts’, when ‘any attempt to demonstrate such an entailment is doomed to failure’ (1996, p. 104). 