A Latin expression that translates as “from the latter”, usually referring to reasoning that is applied backward from an effect to its causes (inferring an effect from its causes). It constitutes knowledge attained after an analysis of an issue or event is conducted.

As an adjective, a posteriori describes relating to, or denoting, all facts (knowledge, reasoning, etc.) available before the deduction or inference of probable conclusions and the next course of action. The available facts are usually derived from a set of observations, experiences, or experimentation results, etc.

As an adverb, a posteriori denotes an occurrence in a way based on reasoning from established facts or past events rather than by making assumptions or predictions.

A posteriori is the opposite of “a priori“, which refers to knowledge obtained prior to an analysis. A posteriori is perceived to be experiential whereas “a priori” is deemed to be universal.