A Treatise Concerning the Principles of Human Knowledge

Berkeley now considers some consequences of the principles he has outlined. First, he declares that many philosophical difficulties disappear when his ideas are accepted. For generations philosophers have struggled to answer questions like “whether corporeal substance can think; whether matter be infinitely divisible; and how it operates on spirit” (64). In particular, a few generations before Berkeley, René Descartes emphasized the problem of how spirit and matter or soul and body interact. Once we accept that matter does not exist, this ceases to be a problem. Indeed, Berkeley goes go on to argue that his system solves many important philosophical problems, notably the problem of skepticism.

His principles lead us to conclude that human knowledge consists of two categories. However, they are not the categories commonly conceived by modern philosophers. The errors of skepticism proceed, according to Berkeley, from the mistaken principle that the two categories of knowledge are things and ideas. Berkeley proposes, instead, that the two categories are ideas and spirits.

Skepticism assumes that material things exist external to our perception and that we conceive ideas about them by perceiving them. Material things are real, and our ideas about them are only real or true insofar as they conform to the truth of material things. The problem then arises of how we can be sure that our ideas conform to the things and are thus true. This is the origin of skepticism.

As an alternative to such skepticism, Berkeley proposes that reality consists of spirits and ideas. The gap between our mind and “the world out there” is closed, and skepticism is eliminated. Truth is a result of our sensations, perceptions, and reflections. Once we accept that “the very existence of an unthinking being consists in being perceived” (66), there can be no more doubt that what we perceive is real and true.

Berkeley attempts to forestall misunderstanding of his doctrine by issuing some clarifications. Berkeley does not believe objects of sense are generated by the mind itself; they are not simply figments of the imagination. Rather, they are “imprinted” on the senses by “a spirit distinct from that which perceives them” (67)—i.e., God. In this sense, and in this sense only, objects of sense may be said to be “external”—meaning that they originate from a spirit other than the one perceiving them. But in any case, it is spirit, and not “inert, unthinking” matter, that carries out this process.

Berkeley’s theory does not detract from “the reality of things” (67). He affirms the real existence of sense objects—books, trees, mountains, etc.; such things exist in the mind of the perceiver, not in the substance “matter.”