 The first is verificationism, according to which a (declarative) sentence is meaningful just in case its truth or falsity can be verified. This entails that unverifiable sentences are literally meaningless, so that no metaphysical claim according to which unobservable nonphysical items exist can be true. However, since our ability to think and talk about our experiences is itself a problem for verificationism, to presuppose this view when attacking the zombie idea would beg the question. The second view appeals to Wittgenstein’s private language argument. Although not crudely verificationistic, it depends on the assumption that in order for words to be meaningful, their use must be open to public checking. But since this checkability assumption, if sound, would prove that we cannot talk about qualia in the ways defenders of the zombie possibility think we can, it too seems question-begging in the present context. According to the third view, behaviorism, there is no more to having mental states than being disposed to behave in certain ways. As a possible basis for attacking the zombie idea, behaviorism is in a similar situation to verificationism and the private language argument. Zombies would satisfy all behavioral conditions for full consciousness, so that if we could know a priori that behaviorism was correct, zombie worlds would be inconceivable for that reason. It seems unlikely, though, that behaviorism can be shown to be correct. (Dennett 1991 defends a position with strong affinities to behaviorism, though it might be better classified as a variety of functionalism). 