Definition of a priori:

part of speech: adjective

The correlative of a posteriori, the one implying the cause, the other the effect. The argument a priori is a mode of reasoning by which we proceed from the antecedent cause to the consequent effect, or from anticipation rather than from experience; mathematical proofs are examples of a priori reasoning. The argument a, posteriori is the opposite, and reasons from the effect to the cause, from the individual case to the law, or generally from experience, and not from anticipation.