  The identity theory as I understand it here goes back to U.T. Place and Herbert Feigl in the 1950s. Historically philosophers and scientists, for example Leucippus, Hobbes, La Mettrie, and d'Holbach, as well as Karl Vogt who, following Pierre-Jean-Georges Cabanis, made the preposterous remark (perhaps not meant to be taken too seriously) that the brain secretes thought as the liver secretes bile, have embraced materialism. However, here I shall date interest in the identity theory from the pioneering papers ‘Is Consciousness a Brain Process?’ by U.T. Place (Place 1956) and H.  Feigl ‘The "Mental" and the "Physical"’ (Feigl 1958). Nevertheless mention should be made of suggestions by Rudolf Carnap (1932, p. 127), H. Reichenbach (1938) and M. Schlick (1935). Reichenbach said that mental events can be identified by the corresponding stimuli and responses much as the (possibly unknown) internal state of a photo-electric cell can be identified by the stimulus (light falling on it) and response (electric current flowing) from it. In both cases the internal states can be physical states. However Carnap did regard the identity as a linguistic recommendation rather than as asserting a question of fact. See his ‘Herbert Feigl on Physicalism’ in Schilpp (1963), especially p. 886. The psychologist E.G. Boring (1933) may well have been the first to use the term ‘identity theory’. See Place (1990).