A priori

An important term in epistemology since the seventeenth century, ‘a priori’ typically connotes a kind of knowledge or justification that does not depend on evidence, or justification, from sensory experience. Talk of a priori truth is ordinarily shorthand for talk of truth knowable or justifiable independently of evidence from sensory experience; and talk of a priori concepts is usually talk of concepts that can be understood independently of reference to sensory experience. A priori knowledge contrasts with a posteriori knowledge, knowledge requiring evidence from sensory experience. Broadly characterized, a posteriori knowledge is empirical, experience-based knowledge, and a priori knowledge is nonempirical knowledge. Standard examples of a priori truths are the truths of mathematics, whereas standard examples of a posteriori truths are the truths of the natural sciences.