Book excerpt: Psychologists and philosophers have assumed that psychological knowledge is knowledge about, and held by, the individual mind. Psychological Knowledge challenges these views. It argues that bodies of psychological knowledge are social institutions like money or the monarchy, and that mental states are social artefacts like coins or crowns. Martin Kusch takes on arguments of alternative proposals, shows what is wrong with them, and demonstrates how his own social-philosophical approach constitutes an advance. We see that exists a substantial natural amount of philosophical theorising, a body of work that tries to determine the nature and structure of folk psychology. An introduction to the workings of constuctivism, Psychological Knowledge is an insightful introduction to the history of psychology and the recent philosophy of mind.