E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A priori [Latin, from an antecedent].
An a priori argument is when we deduce a fact from something antecedent, as when we infer certain effects from given causes. All mathematical proofs are of the a priori kind, whereas judgments in the law courts are of the a posteriori evidence; we infer the animus from the act. (See A POSTERIORI.)