Thus there is no need for explicit use of Ockham's Razor as in Smart (1959) though not in Place (1956). (See Place 1960.) Lewis's paper was extremely valuable and already there are hints of a marriage between the identity theory of mind and so-called ‘functionalist’ ideas that are explicit in Lewis 1972 and 1994. In his 1972 (‘Psychophysical and Theoretical Identifications’) he applies ideas in his more formal paper ‘How to Define Theoretical Terms’ (1970). Folk psychology contains words such as