 A priori and a posteriori

A priori and a posteriori ('from the earlier' and 'from the later', respectively) are Latin phrases used in philosophy to identify two types of knowledge, justification, or argument, characterized by the use of experiential or empirical evidence, or a lack thereof.More precisely, these terms are used with respect to epistemology in order to distinguish between "necessary conclusions from first premises" (i.e., what must come before sense observation, or empirical knowledge) and "conclusions based on sense observation" which must follow it.