The introduction of a small amount of bounded rationality into a model sometimes has little effect, and sometimes has a dramatic impact on predicted behavior. We call a model robust to bounded rationality if small deviations from rationality result only in small changes in the equilibrium set. We also say that a model is structurally stable if the equilibrium set (given fully rational agents) v...

According to one view about the rationality of belief, such rationality is ultimately nothing other than the rationality that one exhibits in taking the means to one’s ends. On this view, epistemic rationality is really a species or special case of instrumental rationality. In particular, epistemic rationality is instrumental rationality in the service of one’s distinctively cognitive or episte...

My aim in this paper is to explore the relationship between epistemic rationality and instrumental rationality. By epistemic rationality, I mean, roughly, the kind of rationality which one displays when one believes propositions that are strongly supported by one's evidence and refrains from believing propositions that are improbable given one's evidence. Prominent epistemologists frequently em...

Recent research in group cognition points towards the existence of collective cognitive competencies that transcend individual group members' cognitive competencies. Since rationality is a key cognitive competence for group decision making, and group cognition emerges from the coordination of individual cognition during social interactions, this study tests the extent to which collaborative and...

Rationality is a fundamental concept in economics. Most researchers will accept that human beings are not fully rational. Herbert Simon suggested that we are “bounded rational”. However, it is very difficult to quantify “bounded rationality”, and therefore it is difficult to pinpoint its impact to all those economic theories that depend on the assumption of full rationality. Ariel Rubinstein pr...

I am honored to present this lecture in tribute to Nancy L. Schwartz. I did not know Professor Schwartz well, yet I am aware of her important professional contributions. First and foremost are the direct advances to the profession made through her writings. But also her indirect contributions, as a teacher and an intellectual leader, are very important. Some of the ideas and applications discus...

Arrow’s impossibility theorem states that if a collective choice rule satisfies unrestricted domain, weak Pareto, independence of irrelevant alternatives, and collective rationality, then there exists a dictator. Among others, Arrow’s postulate of collective rationality is controversial. We propose a new axiom for a collective choice rule, decisiveness coherence, which is weaker than collective...

The paper discusses rationality at two levels. According to a common opinion the key to rationality at the group level is a willingness to contribute unselfishly at the individual level. I claim that even when rationality at the individual level is denied, it is often achieved by social punishment. The difficulty to organize a social project is exaggerated. The relative ease of implementing ind...