What is the role of imagination in a priori knowledge? Here I provide a partial answer, arguing that imagination can be used to shed light on which experiences merely enable knowledge, versus which are evidential. I reach this partial answer by considering in detail Timothy’s Williamson’s recent argument that the a priori/a posteriori distinction is insignificant. There are replies to the argument by Boghossian and Casullo that might work on their own terms, but my reply examines the assumptions that Williamson makes about the role of imagination in knowledge generation. I show that Williamson’s argument does not account for important distinctions from recent discussions of imaginative content. When these distinctions are not ignored, we can see that Williamson’s argument attributes a subject knowledge on the basis of a faulty application of universal generalization. I close by connecting my positive account of the role of imagination in the a priori to a debate about the role of memory in the a priori that played out 25 years ago.