Many philosophers take the distinguishing mark of their subject to be its a priori status. In their view, where empirical science is based on the data of experience, philosophy is founded on a priori intuitions. In this paper I shall argue that there is no good sense in which philosophical knowledge is informed by a priori intuitions. Philosophical results have just the same a posteriori status as scientific theories. My strategy will be to pose a familiar dilemma for the friends of a priori philosophical intuitions. I shall ask them whether their intuitions are supposed to be analytic or synthetic. And then I shall argue that, if the intuitions are analytic, they may be a priori, but will be philosophically uninteresting; while, if they are synthetic, they may be philosophically interesting, but will not merit being treated as a priori in the context of philosophical debate. At the end of the paper I explain that this does not mean that philosophy should abandon ‘armchair’ methods. We still need to uncover and examine the often unrecognized intuitions that drive our thinking. However this is not because they provide a distinctive source of a priori knowledge, but on the contrary because they may be leading us astray.