David Chalmers supports his contention that there is a possible world populated by our zombie twins by arguing for the assumption that conceivability entails possibility. But, I argue, the modal epistemology he sets forth, ‘modal rationalism,’ ignores the problem of incompleteness and relies on an idealized notion of conceivability. As a consequence, this epistemology can’t justify our quotidian judgments of possibility, let alone those judgments that concern the mind/body connection. Working from the analogy that the imagination is to the possible (...) as perception is to the actual, I set forth a competing epistemology, ‘modal empiricism.’ This epistemology survives the incompleteness objection and allows some of our everyday modal judgments to be justified. But this epistemology can’t justify the claim that Zombie World is possible, which leaves Chalmers’s property dualism without the support it needs. (shrink)