 Philosophical zombies pose a serious threat to physicalist views of qualia. To begin with, if zombie replicas are metaphysically possible, then there is a simple argument that seems to show that phenomenal states are not identical with internal, objective, physical states. Suppose objective, physical state P can occur without phenomenal state S in some appropriate zombie replica (in the metaphysical sense of ‘can’ noted above). Intuitively S cannot occur without S. Pain, for example, cannot be felt without pain. So, P has a modal property S lacks, namely the property of possibly occurring without S. So, by Leibniz’ Law (the law that for anything x and for anything y, if x is identical with y then x and y share all the same properties), S is not identical with P.