I make three claims about the interactions between concept mastery and the knowledge argument. First, I argue that, contra Ball, the concept mastery response to the knowledge argument does not suffer from the heterogeneity of concept mastery. Second, I argue that, when doing metaphysics by relating propositions on the basis of whether a hypothetical agent who knew a base collection could infer a target proposition, it is legitimate to rely on propositions that are not contained in the base, as long (...) as those propositions are required for mastery of relevant concepts. One upshot is that, when checking whether the physical truths a priori entail the consciousness truths, it is fair game to rely on substantive truths about consciousness. Third, I argue that the only version of the knowledge argument that has any hope of succeeding against physicalism completely lacks the argument's driving intuition: that Mary learns something new when she emerges from the black and white room. (shrink)