Two kinds of replies to this objection are worth considering. The first, suggested in the brief statement of Quine’s new methodology, is to reject the old problem as based on the false presupposition that one can vindicate scientific and other knowledge on the basis of propositions that are knowable a priori. The difficulty with this response is that it raises the difficult issues of whether a priori knowledge is possible and whether we can determine an answer to that question a posteriori. Anot