Abstract: This chapter provides a taxonomy of widely endorsed conditions on a priori justification. The conditions fall into two broad categories: epistemic, which includes defeasibility, strength, and source conditions; and nonepistemic, which involves the concepts of analyticity or necessity. Two major claims are argued: (1) nonepistemic conditions are neither necessary nor sufficient for a priori justification, and (2) if a theory imposes epistemic conditions on the a priori that differ from those it imposes on the a posteriori, they must be supported by independent argument or rejected as ad hoc. Two defensible conditions on a priori justification emerge: justification by a nonexperiential source, and justification that is not defeasible by experience.

Keywords: analyticity, defeasibility, defeasible, epistemic, experiential, necessity, nonepistemic, nonexperiential, source, strength,