a posteriori adjective 2adverb 1forms 2 adjective2 •Involving induction of theories from facts.What Locke calls "knowledge" they have called "a priori knowledge"; what he calls "opinion" or "belief" they have called "a posteriori" or "empirical knowledge". — 1988 •Of a constructed language, Developed on a basis of languages which already exist. adverb1 •In a manner that deduces theories from facts. formsmore a posteriori · most a posteriori