Principles of Human Knowledge by George Berkeley

Context

The Principles of Human Knowledge was published in 1710, when its author, George Berkeley, was twenty-five years old and a fellow of Trinity College Dublin. The book's full title — A Treatise Concerning the Principles of Human Knowledge, wherein the chief causes of error and difficulty in the Sciences, with the grounds of Scepticism, Atheism, and Irreligion, are inquired into — announces its double ambition: to set philosophy on a sound foundation and to refute the materialism and skepticism that, in Berkeley's view, were the fruit of the philosophy of his age.

The book's target is the philosophy of John Locke and, behind it, the mechanical philosophy of the seventeenth century. Locke had argued that the mind perceives ideas produced in it by an external world of material objects, and that only some of the properties we perceive (the primary qualities) resemble properties in the objects themselves. Berkeley saw this as a recipe for skepticism: if all we perceive are ideas, we have no way to know the material world that supposedly produces them. His response was to deny the material world altogether. The Principles argues that reality consists of minds and their ideas; that "to be is to be perceived"; and that the "material substance" posited by philosophers is a fiction — and a pernicious one, since it leads to skepticism and atheism.

Core Arguments

Esse Est Percipi

Berkeley's fundamental principle is that the existence of the objects of sense consists in their being perceived: "esse est percipi" — to be is to be perceived. The table, the apple, the mountain are collections of ideas — of color, shape, texture, taste — and their existence is nothing over and above their being perceived. Berkeley anticipates the objection that this makes the world dependent on us and argues that it restores the world to us: what we perceive, we perceive directly, and the world of perception is the real world. The doctrine is not skepticism but a reinterpretation of reality: there is no hidden material substratum behind the ideas; the ideas themselves are the things.

The Critique of Material Substance

Berkeley's central critical argument attacks the notion of material substance. The philosophers' "matter" is supposed to be an unperceivable substratum that underlies the perceivable qualities of things. Berkeley argues that this notion is incoherent: we have no idea of matter, since all our ideas come from sensation and reflection, and matter is supposed to be neither an object of sense nor an operation of mind; and matter is useless, since it explains nothing that the ideas themselves do not explain. If no one can perceive matter and nothing requires it, belief in it is groundless. Moreover, since the notion of matter supports skepticism (if reality is hidden behind ideas, we cannot know it), its removal restores the certainty of knowledge.

The Critique of Abstract Ideas

The Principles opens with a critique of abstract ideas, directed at Locke. According to the doctrine of abstraction, the mind can form general ideas — the idea of extension in general, or of triangle in general — by separating common features from particular instances. Berkeley argues that such ideas are impossible: we cannot form an image of a triangle that is neither scalene nor isosceles nor equilateral. Abstract ideas, he holds, are a source of philosophical confusion; general terms function by standing for particular ideas taken as representatives, not by naming abstract entities. This critique influenced the empiricist theory of meaning and was taken up by Hume.

The Role of God

If to be is to be perceived, what becomes of objects when no human perceives them? Berkeley's answer is that God, an infinite spirit, perceives everything at all times. The "real" existence of things consists in their being perceived by God, and human perceivers come to share in that perception. The laws of nature are the regular patterns according to which God presents ideas to finite minds. Far from being an embarrassment, the appeal to God is the keystone of the system: it secures the continuity of the world, the stability of nature, and the refutation of atheism. The Principles concludes that the belief in matter is not merely false but the root of skepticism and irreligion.

Key Concepts

The book's key concepts — esse est percipi, immaterialism, the critique of abstract ideas, the refutation of material substance, and the theocentric account of reality — are the purest expression of idealism in the empiricist tradition. The Principles also introduces Berkeley's famous claim that the distinction between "real things" and "ideas" is to be drawn within the world of perceptions: real things are the ideas that are strong, orderly, and independent of our will (God-given), while imaginary things are the weak, chaotic products of our own imagination.

Legacy & Influence

The Principles is one of the boldest books in the history of philosophy: a complete idealist system built on a single principle. It was largely ignored or ridiculed on publication, but it became, with the Three Dialogues between Hylas and Philonous (1713), the definitive statement of immaterialism, and it permanently changed the course of modern philosophy. Berkeley's critique of the primary-secondary quality distinction, his argument that the objects of perception are directly given, and his insistence that reality is experiential all anticipated central themes of later philosophy: the idealism of Kant, the phenomenology of the twentieth century, and the contemporary debate about consciousness and the external world. Hume, who found Berkeley's arguments unanswerable in principle but incredible in conclusion, was haunted by them; and the question Berkeley posed — whether the world can be known apart from experience — remains at the heart of the philosophy of mind and epistemology. The Principles is also a classic source for the view, defended by David Chalmers and others, that consciousness and experience are more fundamental than matter as we conceive it.

Reading Guide

The Principles is short and divided into a long Introduction (on abstract ideas) and a First Part of ninety sections. The Introduction is essential for Berkeley's method and his critique of Locke. The First Part proceeds from the principle that ideas exist only in minds (sections 1–33) to the critique of material substance (sections 34–84) and the implications for science and religion (sections 85–156). The book was intended to have a Second Part on ethics, which Berkeley lost and never rewrote. Readers who find the abstract style difficult may prefer the Three Dialogues, which presents the same doctrine in livelier form.

Related Works

The Principles is Berkeley's systematic statement, complemented by his Three Dialogues between Hylas and Philonous (1713) and his New Theory of Vision (1709). It responds to John Locke's Essay Concerning Human Understanding and is transformed by David Hume's empiricism. Its idealism connects to philosophy-idealism, its theory of perception to what is consciousness and direct experience, and its critique of substance to the modern debate about dualism and the nature of the mind.