 So far, the standard view may understand the class of a priori propositions too narrowly. Mathematics and logic are regarded as the paradigm a priori disciplines. But it is doubtful that all the mathematical and logical truths we know are self-evident. Many of these truths require proof. When S believes such a proposition, S’s belief will not be based solely on understanding the proposition. S’s experience of constructing the proof will play an important role in S’s justification for believing the proposition proven. If the proof is complex, S’s justification will probably in part rely on memory, e.g., of lemmas proven along the way. The standard view can extend the class of a priori propositions without compromising its basic approach by adding that if S believes P on the basis of proving it from self-evident premises by steps that are self-evidently valid, then S is a priori justified in believing P.