 Consider a third example, from epistemology. A simple causal theory of perceptual knowledge says that a subject’s perceptual knowledge that P can be analyzed in terms of P’s bearing the right kind of causal relation to the subject’s belief that P. To test this claim, we need not await proposals as to what the kind of causal relation in question is. For this project of conceptual analysis can succeed only if two believers that P cannot differ with respect to perceptually knowing that P without differing with respect to how P is causally connected to their belief that P. Alvin Goldman’s fake barn country case (1976) yields a (putative) counterexample to this supervenience claim.