This paper offers an account of the a priori/a posteriori distinction utilizing the insights of reliabilism, focusing on the inputs to reliable belief-forming processes. I propose that a belief possesses a priori justification if it is the result of a reliable belief-producing process whose input is ‘non-sensory’ and the reliability of this process does not ‘causally depend’ on the reliability of a prior process taking in ‘sensory’ input. One of the interesting consequences of this account is in the treatment of introspective knowledge of one’s belief-states; it was classically considered a posteriori, but comes out a priori on this model.