I argue that, contrary to what others have thought (Jonathan Ichikawa, Benjamin Jarvis), mechanisms of evidential support and defeat work in much the same way regardless of whether the propositions involved are a priori or a posteriori. This account of evidential support and defeat for a priori propositions provides a plausible explanation for misleading evidence about what rationality requires, since it makes possible a kind of defeat that alternative accounts make impossible – namely a priori propositional defeat from misleading a priori evidence.