A philosophical theory that something nonmaterial (such as mind or spirit) is the ultimate basis of reality, or that the object of external perception consists of ideas. Idealism is the basis of Berkeley’s philosophy, although the term itself was not coined until after his death; Berkeley himself used the term “immaterialism.”

The philosophy that all knowledge derives from experience, particularly sense experience. It is often contrasted with rationalism, or the theory that knowledge is derived from reasoning. Empiricism dominated British philosophy in Berkeley’s era. Berkeley, John Locke, and David Hume were the major empiricists of the time.

This pair of contrasting terms has relevance for the theory of empiricism. A priori (Latin, “from the one before”) denotes reasoning or knowledge which proceeds from theoretical deduction rather than from observation or experience. A posteriori (Latin, “from the one after”) denotes reasoning or knowledge which proceeds from observation or experience.