  Berkeley’s first important published work, An Essay Towards a New Theory of Vision (1709), was an influential contribution to the psychology of vision and also developed doctrines relevant to his idealist project. In his mid-twenties, he published his most enduring works, the Treatise concerning the Principles of Human Knowledge (1710) and the Three Dialogues between Hylas and Philonous (1713), whose central doctrines we will examine below.