George Berkeley (; 12 March 168514 January 1753) — known as Bishop Berkeley (Bishop of Cloyne) — was an Anglo-Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism" (later referred to as "subjective idealism" by others). This theory denies the existence of material substance and instead contends that familiar objects like tables and chairs are only ideas in the minds of perceivers, and as a result cannot exist without being perceived. Berkeley is also known for his critique of abstraction, an important premise in his argument for immaterialism.