 Even though any person, S, who understands a self-evident proposition, PSE, will be justified in believing PSE to a degree sufficient for knowledge, we cannot say that if S understands PSE and believes PSE, then S will know PSE. We have not yet addressed the connection between self-evidence and truth, but this is not the problem: self-evidence is taken to imply truth. To explain why S could understand and believe PSE but fail to know PSE, it will be helpful to distinguish between propositional justification and doxastic justification.