First published in 1713, this work was designed as a vivid and persuasive presentation of the remarkable picture of reality that Berkeley had first presented two years earlier in his Principles of Human Knowledge. His central 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.