The leading philosopher guides the reader through the ideas that will shape the 21st century. Thought can, and does, change the world, and ideas also evolve - bioethics, fundamentalism and environmentalism are defining the future in the same way that Marxism, feminism and existentialism influenced our past. So what do we need to know for the future? More than a simple reference guide, this is a personal look at the ideas, past and present, that shape our world.