Abstract

Karl Popper’s world 3 theory proposes that the products of the human mind can be considered a third world, partially autonomous of the mental and physical worlds, and real, because it can produce effects on both. When he first introduced the idea in 1960, he took even his close colleagues and students by surprise. Yet tracing the development of his idea shows a great deal in Popper’s previous work and thought led up to what seemed his startlingly new proposal. And far from being the philosophy of his dotage, as some sneered, his world 3 proposal, once fully shaped, became a keystone of his thought.