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...