The topic of a priori knowledge has been central to analytic philosophy for the past two centuries. It was introduced by Kant in his seminal work Critique of Pure Reason and vigorously dismissed by Quine in Two Dogmas of Empiricism, resulting in an epistemological controversy that remains deeply divided to this day. Casullo's book, based on previously published and unpublished work, systematically addresses questions that have, since Kant, formed the core of the debate. One of his central claims is that the concept of a priori has not been well understood and that many of the apparent differences that underlie much of the contemporary debate are a result of these misunderstandings. Casullo's reformulation of this traditional debate is both original and persuasive, and should appeal to a wide range of philosophers who share an interest in epistemology.