A Treatise Concerning the Principles of Human Knowledge Analysis

George Berkeley


The idea that “all those bodies which compose the mighty frame of the world, have not any subsistence without a mind—that their being is to be perceived or known” will hardly seem obvious to anyone unfamiliar with George Berkeley or with idealism. This startling statement has considerable shock value, but it is true to Berkeley’s bold metaphysical thesis that reality is mental or spiritual in nature.

The statement’s emphasis on perception reveals its author’s epistemological and methodological approach: empiricism. Although not all empiricists would accept Berkeley’s conclusions and not all metaphysical idealists would accept his method, none would deny his importance in the traditions of both empiricism and idealism. That his method and even his immaterialism have influenced some modern physicists and that his analytical technique is valued even by such antimetaphysicians as the logical positivists are proofs of the classical status Berkeley’s work has enjoyed.

His aims, however, were primarily those of a metaphysician and theologian; he wished to undermine skepticism and atheism by refuting materialism, to demonstrate God’s existence and immateriality, to show the immortality of the soul, and to clarify current scientific and philosophical confusions. The latter are due, he claimed, not to inherent defects in people’s mental faculties but to their use: “We have first raised a dust and then complain we cannot see.” Berkeley intended to settle this dust and to destroy materialism.


A chief cause of obscurity, Berkeley states, is the doctrine of abstract ideas, the theory that the mind can abstract from particular qualities a clearly conceived notion of what is common to them, but which itself is otherwise like none of them, or that the mind can separate in thought what cannot be separated in reality. An example of the first abstraction would be a notion of color that is neither red, blue, green, and so forth, or of extension that has neither size, shape, line, plane, nor surface; an illustration of the second would be an abstract idea of color or motion without extension.

Berkeley finds such abstraction psychologically impossible and challenges the reader to conceive such an idea as that of a triangle with all of the general and yet none of the specific characteristics of triangles. However, must Berkeley then deny the universality of ideas essential to rational demonstration such as geometrical proofs relevant to all triangles? No—ideas may be general without being abstract; one generalizes particular ideas by temporarily disregarding their unique features, while one’s demonstrations concern only features shared. However, this universality in function must not be mistaken for abstract conception; the latter is actually without content and unintelligible.

Berkeley claims that the confused belief in abstract ideas arises from language: The assumption is that general names signify precise abstract ideas indispensable to thinking and communication, but this is false. Attention should be paid not to words but to ideas themselves. Because ideas are perfectly transparent, being known directly, the verbal controversies and errors springing from abstraction can be avoided. Thus, Berkeley sets the stage for a far-reaching application of the foregoing conclusions to an analysis of the nature and existence of the objects of knowledge.

Objects of Knowledge

The objects of knowledge, Berkeley writes, are ideas of three kinds: sensations, ideas originating in the mind’s own passions and activities, and those of memory and imagination. He first deals with “sensible” objects. Through sight, one knows color; through sight and touch, one knows size and shape; through touch, hardness; and through smelling, odors. Certain constant collections of such ideas are considered one object or thing and accordingly named, such as “apple” or “tree.” However, obviously perceived ideas require a perceiver, and this is spirit or mind, not itself an idea. Careful examination shows that thoughts and ideas have no existence external to minds; hence “sensible” things or physical objects do not exist apart from their perception in minds—esse es percipi: For them to be is to be perceived.

The typical reaction to this conclusion is to accuse Berkeley of denying the reality of the physical world and even the evidence of his senses. However, Berkeley explains that when one says that a table exists, this means that someone sees and feels it or will do so on occasion. The very meaning of “existence” or “being” applied to perceptible objects is exhaustively described in terms drawn from perception—nothing else can meaningfully be said about them. To think that sensible objects or their alleged metaphysical substratum, matter, exist “without” (external to) the mind is to entertain an unintelligible abstraction and a clear contradiction. People commonly think that houses or mountains exist unperceived. However, what are these but objects of the senses? Is it not self-contradictory to think that sensations or ideas exist unperceived? When one imagines that one can think of unperceived objects, one is merely thinking of objects while forgetting the perceiver, but meanwhile one is perceiving or thinking of them. One cannot conceive the inconceivable.

However, the common belief that matter exists even when it is unperceived will not die easily, so Berkeley tries to anticipate every possible objection. One of the first arises from the “representative” theory of perception, which grants that ideas occur only in minds but holds that they represent or copy things outside minds. Berkeley’s most direct answer is that ideas can resemble nothing but other ideas. How could a color represent something...

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Existence and Reality

Yet if his theory is true, can it distinguish reality from illusion—for example, real from merely imaginary fire—since everything perceived consists only of ideas? If there is any doubt, Berkeley answers, put your hand in the real fire, and you will sense a pain lacking in the imaginary one—but can you suppose pain existing externally to a mind? Fantasy and illusion are differentiated from the real world by obvious differences in their ideas; those of the latter are more vivid, constant, and coherent; their regular, predictable order constitutes the laws of nature, and they are independent of people’s wills as imagination is not. In fact, this independence marks the one legitimate sense in which one speaks of “external objects”; sensed qualities are external to finite spirits’ wills but not to that of the eternal Spirit, God, of whose will they are a perceptible expression.

Critics point out that if the existence of things depends on perception, they will exist and cease to exist with the occurrence and cessation of perception, and therefore, this theory is absurd. Berkeley counters by asking whether the statement that a table continues to exist when everyone leaves the room means anything more than that if one were still there one would perceive it, or if one were to return, one would once again see it. >From the reliability of nature’s order, one can both reconstruct the past and predict the future, in neither of which are...

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The Infinite Spirit

Suppose, however, that one grants both the existence of this Spirit and the extremely complicated mechanism of nature. To what purpose did God create such a powerless machine if he wished merely to communicate with finite minds? Why not do it directly? Berkeley meets this objection by observing that if anything were superfluous, it would be an unknowable, ineffectual corporeal substance; it is possible, on the other hand, to give a rationale for nature.

Its orderly mechanism, while not indispensable to God, is still instrumental to human learning and profit. Observing the conjunction of fire and heat, people learn not that the idea of fire causes the idea of heat, but that the former signifies that the latter will follow. Single ideas are like words, and the laws of nature like the grammar of a language; however, just as it is unwise to study only grammar and neglect meaning, so it is folly for science to concentrate only on mechanical laws and neglect the final causes (purposes) they express, those determined by God’s wisdom and goodness. This does not derogate from science, but redirects it to explication of phenomena as signs rather than as effects of physical causes. Thus the hypothesis of matter is unnecessary even to physics.

Why, then, is belief in matter so pervasive? Partly because people found that objects of sensation seemed to be independent of themselves and thus supposed that such ideas exist externally. Philosophers saw the error of this supposition, but in trying to correct it by positing the external existence of matter, they substituted another mistake, unaware of the internal contradictions involved. Furthermore, the operations of the eternal Spirit are so lawful that it was not imagined they were those of a free spirit rather than those of rigidly mechanical causes; and although they clearly point to his being, still there is no collection of sensed qualities making God visible or tangible as people are.

In the foregoing considerations, the existence of spirit has been assumed on the basis of only one...

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Additional Reading

Berman, David. Berkeley. New York: Routledge, 1999. An excellent biographical introduction to the thoughts of the philosopher, clearly presented and requiring no special background. Bibliography.

Berman, David. George Berkeley: Idealism and the Man. New York: Oxford University Press, 1994. This worthwhile analysis of George Berkeley’s distinctive philosophical positions focuses on his religious thought. Contains considerable information about Berkeley’s life and his considerable influence.

Bonk, Sigmund. “We See God”: George Berkeley’s Philosophical...

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