George Berkeley (1685–1753) proposed a radical solution to the conundrums of modern philosophy. By denying the existence of matter, he dismissed the problem of how we can know a world outside our minds. Only minds and their ideas are real. The problem of understanding how mind and matter interact is dissolved by Berkeley’s immaterialism, and so is the difficulty of explaining how causation works. The source of all that we perceive, he believed, is God. Few philosophers have ever accepted this position. But the brilliance of his arguments for it earned him a place in the Western philosophical canon.