Modern economics and psychology originated with the rationalist philosophers of the eighteenth century. Both disciplines claim Jeremy Bentham as an ancestor, although soon after his day they went their very separate ways. One of Bentham’s shrewd psychological observations was that the second cup of coffee or the second helping of a dish is less enjoyable than the first, and the economists enshrined it into their celebrated Law of Diminishing Marginal Utility. But in the twentieth century they expurgated even that tiny bit of psychology, and today the economist’s theory of consumer behavior is limited to exploring the logical implications of the assumption of man’s rationality. It is now believed, however, that even the biological and learned drives cannot explain all behavior, and that a more general framework is needed to supplement or supplant the drive theory.
