This text, written as Three Dialogues, was designed as an accessible presentation of the remarkable picture of reality that Berkeley had first presented in his Principles of Human Knowledge. His striking claim there, as here, was that physical things consist of nothing but ideas in minds - that the world is not material but mental. Berkeley uses this thesis as the ground for a new argument for the existence of God, and the dialogue form enables him to raise and respond to many of the natural objections to his position.