In this book, Edward Stein offers a clear critical account of the debate about rationality in philosophy and cognitive science. He discusses concepts of rationality--the pictures of rationality on which the debate centers--and assesses the empirical evidence used to argue that humans are irrational. He concludes that the question of human rationality must be answered not conceptually but empirically, using the full resources of an advanced cognitive science. Furthermore, he extends this conclusion to argue that empirical considerations are also relevant to the theory of knowledge--in other words, that epistemology should be naturalized.