Abstract:
The rational utility maximization hypothesis (RUMH) was not always a part of economics. Most Classical economists believed that people are influenced by passions as well as by reason. The RUMH became a central part of economics when mathematics became a primary tool of analysis. This was not a coincidence, as the change in method led to the ascendancy of the RUMH. Motivated by recent experimental evidence, it is suggested that the marginal trader hypothesis be invoked to allow a modification of the RUMH: When arbitrage is possible, only a small fraction of market participants need be assumed rational.