How did George Berkeley’s idealism differ from realism about material objects?

George Berkeley’s idealism differs from realism regarding the nature and independence of material objects. While realism maintains that material things exist independently of being perceived or related to any mind, Berkeley argued that reality consists exclusively of minds (spirits) and their ideas.12

Key differences include:

• Nature of Objects: Realists typically posit that material objects possess an existence independent of cognitive activity. In contrast, Berkeley argued that "to be is to be perceived" (esse est percipi). He contended that sensible objects—such as a pen or a table—are composed entirely of ideas, which exist only within a mind.23145
• Rejection of Substrate: Unlike philosophers such as John Locke, who proposed that properties inhere in an imperceptible "material substrate," Berkeley rejected this as unintelligible. He argued that there is no "stuff" behind our perceptions; objects are simply collections of sensible qualities (ideas) like extension and color.415
• Independence: Realism requires that objects exist even when not perceived. Berkeley, however, maintained that objects remain "real" even when not currently perceived by a human, because they are still perceivable and exist in relation to the mind of God.15

Ultimately, while Berkeley affirmed the existence of the objects we perceive, he redefined them as mental entities rather than mind-independent material substances.45