Epistemology is the study of knowledge. Within the study of knowledge are two categories of knowledge—a priori and a posteriori.
A priori knowledge is knowledge that is not based on observation of the physical world. The term a priori comes from two Latin words. A means “from” and priorimeans “that which comes before.” Thus, a priori knowledge is knowledge that exists in the mind before any experience with or observation of the physical world. The classic example of an a priori truth is mathematics which can be known and verified apart from experience.
A posteriori knowledge, on the other hand, is knowledge that comes directly from observation of the physical world. The term a posteriori means “from what comes later” and, thus, refers to knowledge that comes as a result of experiencing the physical world.
Great debate has existed throughout the history of philosophy concerning whether our knowledge is primarily a priori or a posteriori. Rene Descartes was a big proponent ofa priori knowledge while others like John Locke and David Hume stressed that all of our knowledge comes from experience. In fact, Locke argued that our minds are atabula rasa or “blank slate” at birth. It is only through experience oft the world that we gain knowledge.