Second, the zombie argument assumes the philosophical idea of necessary truths as statements that must be true, in contrast to ones that are true only of our world. As I argued in Chapter 2, the concept of necessity is inherently problematic. We cannot simply say that necessity is truth in all possible worlds, since necessity and possibility are interdefinable: something is possible if its negation is not necessarily false. Nor can we define possibility in terms of conceivability, since what is conceivable at any time is not absolute, but merely a contingent function of the available concepts and beliefs. It is also not effective to say that something is possible if it is consistent with the laws of logic, since there is much debate concerning what the laws of logic are. I described in Chapter 2 how even the
principle of noncontradiction, that no statement can be both true and false, has been disputed. Hence the claim that such identity statements as “minds are brains” must be necessarily true is ill specified and should not be used to challenge a claim for which there is substantial evidence. Chapter 5 will provide more specific evidence that emotional conscious experiences are brain processes, along with a theory that makes it clear why philosophical intuitions should not be mistaken for evidence.