The book Moral Tribes: Emotion, Reason, and the Gap between Us and Them, by Joshua Greene, invites the reader to give a new look at the foundation of ethics and, by implication, to policy. Its specific strength is the systematic integration of new methods from neuroscience into a very old debate. Having something new and substantial to add in an investigation that has been at the center of the philosophical debate in Western civilization for twenty-five centuries is remarkable. While I invite everyone to read and enjoy this wonderful book, I take here the opportunity to invite economists to take the challenge. We are particularly interested in the question, “Is there a specific contribution that economics can give to this debate?” I believe there is and this insight is now in danger of being lost. This is my attempt to indicate where the research should look now. Maybe it is not too late. (JEL D12, D63, D87, Z13)

We study the indeterminacy of equilibria in infinite horizon capital accumulation models with technological externalities. Our investigation encompasses models with bounded and unbounded accumulation paths, and models with one and two sectors of production. Under reasonable assumptions we find that equilibria are locally unique in one-sector economies. In economies with two sectors of production it is instead easy to construct examples where a positive external effect induces a two-dimensional manifold of equilibria converging to the same steady state (in the bounded case) or to the same constant growth rate (in the unbounded case). For the latter we point out that the dynamic behavior of these equilibria is quite complicated and that persistent fluctuations in their growth rates are possible.

Adaptive Coding is the property of the brain to adjust its response to statistical properties of the environment. Its effect is an improved discrimination among signals under the constraints on the dynamic range of its response. It can thus be considered the neural correspondent of Rational Attention, which models how a rational decisionmaker allocates attention among different informative signals. There is strong evidence of existence of widespread adaptive coding. Adaptive coding introduces a dependence of choice from the environment which is not observed in behavior. We discuss potential solutions and propose Hebbian learning as a potentially satisfactory answer.

Economists usually assume that monetary incentives improve performance, and psychologists claim that the opposite may happen. We present and discuss a set of experiments designed to test these contrasting claims. We found that the effect of monetary compensation on performance was not monotonic. In the treatments in which money was offered, a larger amount yielded a higher performance. However, offering money did not always produce an improvement: subjects who were offered monetary incentives performed more poorly than those who were offered no compensation. Several possible interpretations of the results are discussed.

We introduce a game of complete information with multiple principals and multiple common agents. Each agent makes a decision that can affect the payoffs of all principals. Each principal offers monetary transfers to each agent conditional on the action taken by the agent. We characterize pure-strategy equilibria and we provide conditions—in terms of game balancedness—for the existence of an equilibrium with an efficient outcome. Games played through agents display a type of strategic inefficiency that is absent when either there is a unique principal or there is a unique agent.

We provide an axiomatic foundation for decision making in a complex environment. We do not assume that the decision maker has complete structural knowledge of the environment. Instead the agent knows the set of actions he can take, he formulates preferences directly on the actions, and chooses according to these preferences. On the basis of experience he modifies these preferences according to a systematic procedure. Our axioms are imposed on this procedure, rather than directly on the choice itself. The axioms consists of a group of natural structural restrictions and a group of independence axioms. Our main result is an axiomatic foundation for a set of simple adaptive learning procedures which include the replicator dynamic.

Gender gaps may be observed in a variety of economic and social environments. One of the possible determining factors is that men are more competitive than women and so, when the competitiveness of the environment increases, the performance of men increases relative to that of women. We test this hypothesis in a field study conducted with 9-year old children, running on a track. They first run alone and then in pairs over a short distance with different gender composition of the pairs. The results support the hypothesis that performance in competition varies according to gender. When children ran alone, there was no difference in performance. In competition boys, but not girls, improved their performance. This finding relates to the discussion regarding single sex schools: the outcomes of examinations in a mixed sex school can show a gender gap in favor of boys, even when this gap does not reflect actual abilities. Girls who are as talented as boys will end up performing worse just because they are not as competitive, and will not achieve as high scores in examinations as boys.

“My own behaviour baffles me. For I find myself not doing what I really want to do but doing what I really loathe.” Saint Paul What behaviour can be explained using the hypothesis that the agent faces temptation but is otherwise a “standard rational agent”? In earlier work, Gul and Pesendorfer (2001) use a set betweenness axiom to restrict the set of preferences considered by Dekel, Lipman and Rustichini (2001) to those explainable via temptation. We argue that set betweenness rules out plausible and interesting forms of temptation including some which may be important in applications. We propose a pair of alternative axioms called DFC, desire for commitment, and AIC, approximate improvements are chosen. DFC characterizes temptation as situations in which given any set of alternatives, the agent prefers committing herself to some particular item from the set rather than leaving herself the flexibility of choosing later. AIC is based on the idea that if adding an option to a menu improves the menu, it is because that option is chosen under some circumstances. From this interpretation, the axiom concludes that if an improvement is worse (as a commitment) than some commitment from the menu, then the best commitment from the improved menu is strictly preferred to facing that menu. We show that these axioms characterize a natural generalization of the Gul-Pesendorfer representation.

Ž. We extend Kreps’ 1979 analysis of preference for flexibility, reinterpreted by Kreps Ž. 1992 as a model of unforeseen contingencies. We enrich the choice set, consequently obtaining uniqueness results that were not possible in Kreps’ model. We consider several representations and allow the agent to prefer commitment in some contingencies. In the representations, the agent acts as if she had coherent beliefs about a set of possible future Ž. ex post preferences, each of which is an expected-utility preference. We show that this set of ex post preferences, called the subjectie state space, is essentially unique given the restriction that all ex post preferences are expected-utility preferences and is minimal even without this restriction. Because the subjective state space is identified, the way ex post utilities are aggregated into an ex ante ranking is also essentially unique. Hence when a representation that is additive across states exists, the additivity is meaningful in the sense that all representations are intrinsically additive. Uniqueness enables us to show that the size of the subjective state space provides a measure of the agent’s uncertainty about future contingencies and that the way the states are aggregated indicates whether these contingencies lead to a desire for flexibility or commitment.

anonymous referees for comments and Tel–Aviv University for its hospitality during part of the work on this paper. Dekel thanks the NSF and Lipman thanks SSHRCC for financial support for this research. Dekel and Lipman particularly thank Phil Reny for a series of discussions which led to this project. This paper was formerly titled “Possibility Correspondences Preclude Unawareness.” 2