A prominent term in theory of knowledge since the seventeenth century, ‘a posteriori’ signifies a kind of knowledge or justification that depends on evidence, or warrant, from sensory experience. A posteriori truth is truth that cannot be known or justified independently of evidence from sensory experience, and a posteriori concepts are
concepts that cannot be understood independently of reference to sensory experience. A posteriori knowledge contrasts with a priori knowledge, knowledge that does not require evidence from sensory experience. A posteriori knowledge is empirical, experience-based knowledge, whereas a priori knowledge is non-empirical knowledge.
Standard examples of a posteriori truths are the truths of ordinary perceptual experience and the natural sciences; standard examples of a priori truths are the truths of logic and mathematics. The common understanding of the distinction between a posteriori and a priori knowledge as the distinction between empirical and non-empirical knowledge comes from Kant’s Critique of Pure Reason (1781/1787).