 To sum up, the standard view holds that a priori knowledge is justified independently of experience, where this means experience beyond the experience required to understand the relevant proposition. There are certain special, self-evident propositions that are propositionally justified for any person who understands them. If a person believes a self-evident proposition solely on the basis of understanding it, the person will be doxastically justified in believing it. Such propositions are often referred to as a priori, which should be taken to mean that it is possible for one to be a priori justified in believing them. By extension, propositions are also a priori if they can be deduced from self-evident premises via steps that are self-evidently valid. A person who believes such a proposition on the basis of such a proof will be a priori justified in believing it. It is also possible to be empirically justified in believing an a priori proposition, but one cannot be a priori justified in believing empirical  propositions.[2]