 In a forthcoming essay in a book in which Williamson and Paul Boghossian debate the a priori (forthcomingb), Boghossian defends three different ways (none of which involve the method of simulation) by which we might be a priori justified in believing a proposition: two ways in which our understanding might be the source of a priori justification, and a third way that appeals to rational intuitions that do not have a distinctive phenomenology and, according to Boghossian, are not the product of our understanding concepts.