epistemology George Berkeleyphilosophy

The next great figure in the development of empiricist epistemology was George Berkeley (1685–1753). In his major work, Treatise Concerning the Principles of Human Knowledge (1710), Berkeley asserted that nothing exists except ideas and spirits (minds or souls). He distinguished three kinds of ideas: those that come from sense experience correspond to Locke’s simple ideas of perception; those that come from “attending to the passions and operations of the mind” correspond to Locke’s ideas of reflection; and those that come from compounding, dividing, or otherwise representing ideas correspond to Locke’s compound ideas. By “spirit” Berkeley meant “one simple, undivided, active being.” The activity of spirits consists of both understanding and willing: understanding is spirit perceiving ideas, and will is spirit producing ideas.

For Berkeley, ostensibly physical objects like tables and chairs are really nothing more than collections of sensible ideas. Since no idea can exist outside a mind, it follows that tables and chairs, as well all the other furniture of the physical world, exist only insofar as they are in the mind of someone—i.e., only insofar as they are perceived. For any nonthinking being, esse est percipi (“to be is to be perceived”).

The clichéd question of whether a tree falling in an uninhabited forest makes a sound is inspired by Berkeley’s philosophy, though he never considered it in these terms. He did, however, consider the implicit objection and gave various answers to it. He sometimes says that a table in an unperceived room would be perceived if someone were there. This conditional response, however, is inadequate. Granted that the table would exist if it were perceived, does it exist when it is not perceived? Berkeley’s more pertinent answer is that, when no human is perceiving a table or other such object, God is; and it is God’s thinking that keeps the otherwise unperceived object in existence.

Although this doctrine initially strikes most people as strange, Berkeley claimed that he was merely describing the commonsense view of reality. To say that colours, sounds, trees, dogs, and tables are ideas is not to say that they do not really exist, it is merely to say what they really are. Moreover, to say that animals and pieces of furniture are ideas is not to say that they are diaphanous, gossamer, and evanescent. Opacity, density, and permanence are also ideas that partially constitute these objects.

Berkeley supports his main thesis with a syllogistic argument: physical things—such as trees, dogs, and houses—are things perceived by sense; things perceived by sense are ideas; therefore, physical things are ideas. If one objects that the second premise of the syllogism is false—people sense things, not ideas—Berkeley would reply that there are no sensations without ideas and that it makes no sense to speak of some additional thing that ideas are supposed to represent or resemble. Unlike Locke, Berkeley did not believe that there is anything “behind” or “underlying” ideas in a world external to the mind. Indeed, Berkeley claims that no clear idea can be attached to this notion.

One consequence of this view is that Locke’s distinction between primary and secondary qualities is spurious. Extension, figure, motion, rest, and solidity are as much ideas as green, loud, and bitter are; there is nothing special about the former kind of idea. Furthermore, matter, as philosophers conceive it, does not exist, and indeed it is contradictory. For matter is supposedly unsensed extension, figure, and motion; but since extension, figure, and motion are ideas, they must be sensed.

Berkeley’s doctrine that things unperceived by human beings continue to exist in the thought of God was not novel. It was part of the traditional belief of Christian philosophers from Augustine through Aquinas and at least to Descartes that God not only creates all things but also keeps them in existence by thinking of them. According to this view, if God were ever to stop thinking of a creature, it would immediately be annihilated.