George Berkeley was an influential 18th century Anglo-Irish philosopher best known for developing the theory of subjective idealism. His central argument was that physical objects do not exist independently of minds perceiving them - in his famous phrase, "to be is to be perceived" (esse est percipi). Berkeley's most important works include "A Treatise Concerning the Principles of Human Knowledge" and "Three Dialogues between Hylas and Philonous," in which he laid out his immaterialist philosophy.