A posteriori

In epistemology, a priori (‘from the earlier’) and a posteriori (‘from the later’) are the two categories of knowledge, justification, or argument, determining whether or not a proposition is reliant on outside sensory experience. Roughly speaking, a proposition is known or justified a priori if it is known or justified independently of any experience (beyond the experience necessary to understand the proposition). It is known or justified a posteriori if its knowledge and/or justification depends on empirical evidence. For example, the proposition ‘It is sunny in London today’ can be known (if true) a posteriori, whereas the proposition ‘Either it is sunny or it is not sunny in London today’ can be known a priori.