 The early functionalist theories of Putnam (1960, 1967) can be seen as a response to the difficulties facing behaviorism as a scientific psychological theory, and as an endorsement of the (new) computational theories of mind which were becoming increasingly significant rivals to it. (But see Putnam 1988, for subsequent doubts about machine functionalism, Chalmers 1996b, for a response, and Shagrir 2005, for a comprehensive account of the evolution of Putnam's views on the subject)