Mr. Sims’s argument suggests that it may be rational for busy people not to balance their checkbooks if they feel they don’t have the time, though they know they will make mistakes as a result.

But if people feel that the work of balancing a checkbook is just too unpleasant, it’s less obvious how to classify their behavior. Some kinds of inattention are even harder to categorize. What about people who decide they don’t have the time to read the news thoughtfully enough to consider whether they will buy a house during a boom, and thus make decisions based on nothing more than hearsay and emotions?

Such questions aren’t confined to economics. Political science has a similar conflict. People often seem emotionally involved — even irrational — when talking politics. In their 1996 book, “Pathologies of Rational Choice Theory,” Donald Green and Ian Shapiro, two political scientists, describe their colleagues’ “highly charged debates about the merits of rational choice theory.”

Other sciences are approaching such questions in novel ways. Brain-imaging techniques are improving our understanding of the cognitive neuroscience of attention, revealing the physical structures that allow us to process information as well as we do, and giving material form to some of the abstract notions in Mr. Sims’s theory of rational inattention. This research, identifying physical structures that underlie our thinking, has a welcome concreteness.

Neuroscience is also showing important links between people’s emotions and behavior they consider rational. In his 1994 book “Descartes’ Error,” the neuroscientist Antonio Damasio considered the admonition of the philosopher Descartes to keep emotions away from our rational thinking. Mr. Damasio examined research finding that emotional pathways in the brain are interlinked with our calculating, ostensibly rational counterparts.

The neuroeconomist Ernst Fehr at the University of Zurich — who I hope will someday become a Nobel laureate himself — has used functional magnetic resonance imaging, or fMRIs, to study people playing games involving economics and finance. His summary of his and many colleagues’ research shows unequivocally that there are links between rational and emotional decision-making. When a game player makes an apparently calculated, rational decision to take an aggressive action against his opponent, emotional and social pathways light up as well, suggesting that the decision wasn’t entirely rational.

The question is not simply whether people are rational. It’s about how best to describe their complex behavior. A broader notion of irrationality may someday be reconciled with one of rationality, and account for actual human behavior. My bet is that real progress will come from outside economics — from other social sciences, and even from information sciences and computer engineering.