A Treatise Concerning the Principles of Human Knowledge

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.

A trend in philosophy involving the application of universal doubt, particularly regarding the trustworthiness of sensory knowledge and reasoning. In its extreme form, skepticism expresses the conviction that “certain knowledge is impossible.” However, in a broader sense, skepticism has been applied throughout the history of philosophy as a means of questioning the claims of received teachings. Part of Berkeley’s goal in the Treatise is to argue against skepticism and affirm the trustworthiness and intelligibility of reality as we experience it. 

In philosophy, the belief that matter is all that exists. Berkeley’s own idealist theory (positing that all reality is spiritual) diametrically opposes materialism.

In Berkeley’s philosophy, spirit is one of the two main components of reality. He defines spirit as that which “acts” and “perceives.” God is a spirit, and so are animals and human beings. Berkeley often uses spirit as synonymous with mind.

The other main component of reality, along with spirit. For Berkeley, everything that is not a spirit is an idea. An idea is defined as that which is perceived. For Berkeley, everything we perceive in the world around us consists of ideas.