Psychological versus economic models of bounded rationality

That the rationality of individual people is ‘bounded’ – that is, finite in scope and representational reach, and constrained by the opportunity cost of time – cannot reasonably be controversial as an empirical matter. In this context, the paper addresses the question as to why, if economics is an empirical science, economists introduce bounds on the rationality of agents in their models only grudgingly and partially. The answer defended in the paper is that most economists are interested primarily in markets and only secondarily in the dynamics of individual decisions – specifically, they are interested in these dynamics mainly insofar as they might systematically influence the most useful approaches to modeling interesting markets. In market contexts, bounds on rationality are typically generated by institutional and informational properties specific to the market in question, which arise and are sustained by structural dynamics that do not originate in or reduce to individuals' decisions or psychological dispositions. To be sure, these influences interact with psychological dispositions, so economists have reason to attend to the psychology of valuation. But no general model of bounded rationality should ever be expected to feature in the economist's toolkit, regardless of the extent to which psychologists successfully identify specific human cognitive limitations. Use of moderate rational expectations assumptions should be understood in this light. Such assumptions are readily relaxed in specific applications, and in ways customized to modeling circumstances, that modelers, experimentalists, and econometricians are making steadily more sophisticated.