A Posteriori

A Posteriori (Latin, “from what comes after”), relating to that which is known through experience, a central concept in epistemology. Those who argue that a posteriori knowledge is the only true knowledge, advocates of empiricism, insist that all we can ever know is that which is accessible to us through experience, mainly sense perception. They therefore deny the plausibility of a priori knowledge as being untestable and thus worthless. David Hume, for example, developed his empirical scepticism to the extent that he denied the existence of the self, claiming that it was unknowable and that human beings were “bundles of perceptions”.

While rationalist philosophers can allow for the existence of both a priori and a posteriori knowledge, empiricists deny the validity of a priori knowledge completely. That is not, however, to deny the validity of analytic truths (for example, the statement “all brown dogs are dogs” is necessarily true, regardless of any real experience of brown dogs), which can be known by virtue of the meaning of the words alone. But such truths are viewed on a different level from the real pursuits of epistemology: John Locke described them as “trifling”, and John Stuart Mill as “merely verbal” because they offer no new knowledge.