This paper examines a market with asymmetric information where there are many signals available and where both the costs of signaling and the product value may depend on many privately known characteristics. Under a weak condition on the relationship between the marginal cost of increasing the signals and the product value, a separating set exists whereby the value of every seller's product is inferred from the seller's optimal choice of signals. The separating set constructed is Pareto dominant and corresponds to recently proposed equilibrium notions in signaling and screening models. Copyright 1987 by The Econometric Society.

Governments often seek influence beyond their borders. One way is through what Thomas Schelling (1960, 1966) calls brute force, taking direct physical control. Less extreme methods are to promise rewards for taking desired actions, or to threaten punishments for not carrying them out-sanctions. Sanctions involve two parties, the sender and the target. (To help identify pronouns' antecedents, we consider a feminine sender and masculine target.) The sender's objective is to influence the target by threatening to impose some measure against him for acting contrary to her interest. Sanctions have long been important in international relations. Athens imposed a trade embargo against Megara, ultimately setting off the Peloponnesian War (431-404 BC). Sanctions are central to such international agreements as the United Nations Charter, the World Trade Organization, and the Montreal Protocol governing chlorofluorocarbons. U.S. law prescribes the use of sanctions in circumstances related, for example, to national security, human rights, intellectual property, and international trade.' Do sanctions actually achieve senders' objectives? A common claim is that they usually fail and are costly to senders. Recent U.S. legislation proposes to limit unilateral U.S. sanctions (except trade-related ones), on the grounds that they cost more than they are worth. History provides examples of sanctions that were costly and ineffectual, such as the League of Nations sanctions against the Italian occupation of Abyssinia, or U.S. sanctions against Cuba. United Nations sanctions against Iraq remain in place, having achieved less than full success, to say the least (see Gary Hufbauer et al., 1990). More systematic studies suggest that sanctions often do succeed, particularly when objectives are modest. Hufbauer et al. (1990) examine 116 episodes of sanctions with military or political objectives, deeming about one-third successful. Sanctions imposed under U.S. trade law have worked even better, about three-fourths of the time (see e.g., Sykes, 1992; Thomas Bayard and Kimberly A. Elliott, 1994; Elliott and J. David Richardson, 1997). Here we develop a simple framework to explain how sanctions can worl, and what is required for them to succeed. Our framework exploits advances in the theory of repeated games and bargaining under incomplete information. While a game-theorist would recognize the flavor of our results, the setting here is a fresh one.2 We find success more likely when the threatened measure costs the sender little relative to the gain from modifying the target's behavior, while the damage to the target is large relative to his cost of complying with the sender's will-results consistent with both intuition and empirical evidence (as well as with Adam Smith [1776 Book IV, Ch. I]). Moreover, a more patient sender is more likely to succeed, while the target's patience can work to the sender's disadvantage.3

Sanctions are measures that one party (the sender) uses to influence another (the target). Sanctions, or the threat of sanctions, have been used by governments to alter the human rights, trade, or foreign policies of other governments. We develop notions of the sender's and target's toughness that depend on their patience and on the extent of their suffering from sanctions. How much a sender can exact from the target depends on the relative toughness of the two. Sanctions that impose less harm on the target can sometimes be more effective than those that impose greater harm.

Sanctions are measures that one party (the sender) uses to influence another (the target). Sanctions, or the threat of sanctions, have been used by governments to alter the human rights, trade, or foreign policies of other governments. We develop notions of the sender's and target's toughness that depend on their patience and on the extent of their suffering from sanctions. How much a sender can exact from the target depends on the relative toughness of the two. Sanctions that impose less harm on the target can sometimes be more effective than those that impose greater harm.

Alternating price competition between firms selling differentiated products to nonhomogeneous consumers can yield two different types of equilibria. One, which we call "disciplined, " arises when products are close substitutes. Another, which we call "spontaneous, " emerges when products are more differentiated. In disciplined equilibria, an implicit threat to cut price further, in response to an initial price cut, supports quite collusive outcomes, which become less collusive as product differentiation increases. In spontaneous equilibria, no such threat is needed. Consumers in the smaller market tend to pay a higher price, as do consumers served by the more efficient firm. Copyright 1990 by The Econometric Society.

The problem of the existence of a competitive equilibrium in models with hidden knowledge and self-knowledge has been discussed previously by M. Rothschild and J. E. Stiglitz_(1976), C. A. Wilson_(1977), and J. G. Riley_(1979). Recent analyses of such models by I. Cho and D. Kreps_(1986) and Riley argue for a particular outcome - the Pareto-dominant separating, zero-profit one. The authors prove the existence of such an outcome under very general conditions and, generalizing the reactive equilibrium concept introduced by Riley, they prove this outcome is the unique reactive equilibrium. Copyright 1987 by The Econometric Society.

This paper provides a theoretical explanation for the persistent use of alphabetical name ordering on academic papers in economics. In a context in which market participants are interested in evaluating the relative individual contribution of authors, it is an equilibrium for papers to use alphabetical ordering. Moreover, it is never an equilibrium for authors always to be listed in order of relative contribution. In fact, we show via an example that the alphabetical name ordering norm may be the unique equilibrium, althoug multiple equilibria are also possible. Finally, we charaterize the welfare properties of the noncooperative equilibrium and show it to produce research of lower quality than is optimal and than would be achieved if coauthors were forced to use name ordering to signal relative contribution.