Berkeley's Idealism: Esse Est Percipi

George Berkeley (1685–1753), Anglo-Irish bishop of Cloyne from 1734, laid out his central metaphysical thesis in two closely related works written while still a young fellow of Trinity College Dublin: A Treatise Concerning the Principles of Human Knowledge (1710) and, cast in more accessible dialogue form to answer objections to the first book, Three Dialogues between Hylas and Philonous (1713). Berkeley's guiding formula, esse est percipi ("to be is to be perceived"), asserts that the very existence of ordinary physical objects — tables, mountains, rivers — consists in nothing more than their being perceived by some mind, or in their capacity to be perceived; for Berkeley there is, strictly speaking, no such thing as unperceived, mind-independent matter at all. Sensible objects, on this account, just are collections or "bundles" of ideas — a particular color, a particular shape, a particular texture, experienced together and given a common name such as "apple" — and since an idea can exist only in a mind that perceives it, it follows immediately, for Berkeley, that sensible objects cannot exist except as perceived.