Contenu du sommaire : Qu'a-t-on appris sur la concurrence imparfaite depuis Cournot ?

Broadly speaking, Cournot's legacy to economics consists of (i) showing economists how to use mathematics in a general way to develop economic theory, as opposed to using examples based on specific functional forms, (ii) his clear and sophisticated treatment of market demand, monopoly, competitive markets, and above all, oligopoly. Among contemporary economists Cournot is mainly remembered only for his oligopoly theory ; however, he appears to have had a formative influence on Marshall and Walras as well as a lesser influence on later mathematically inclined economists.

This paper aims at providing an overview of what has been accomplished in the economics of imperfect competition. Our starting point is that imperfect competition arises when at least one of the four traditional assumptions of perfect competition is violated. In our review, we neglect the monopoly case and offer a brief survey of general equilibrium model with imperfect competition.

For a long time, the analysis of the Compatibility of firm strategies with the rules of Competition Law was the Lawyers private domain. It can't be denied, however that the interest some economists have more lately shown in this field, has greatly helped to improve some juridical decisions.The Game Theory for instance has definitely been helpful in the detection of collusive situations, as indeed the Theory of Contestable Markets when dealing with merging projects.dominant positions, and industries newly opened to competition. Similarly the economists have largely contributed to the working out of the new competition law regulations. The latest legal framework concerning vertical agreements for instance, as well as the leading decision of the Commission make clear reference to the Agency and Transaction Coasts theories. Besides, in its appraisal of R&D agreements, the Commission seems to make use of the production theory.

In 1934, two years before the General Theory publication, H. von Stackelberg published his main work : Marktform und Gleichgewicht. In this book, he presents the well known markets forms typology, and his duopoly theory. Stackelberg explicitly owns to the Cournot, Bowley, Pareto tradition. This text is of interest for two main reasons. It is, in a way, very close to contemporary texts of british economists, revisiting A. Marshall after Sraffa's paper on increasing returns to scale (Harrod, Chamberlin et Robinson). He also concludes to the utility of some institutional forms in order to guaranty the consistence of the economic and social system. He revendicates explictly Italian's texts (such as Amoroso) and political systems. He raises the question of the relationship between the economic theory and the choice of institutional forms.

In a simple model of horizontal differentiation with free entry (entry occurring in a preliminary stage), it is shown that "tough" price competition, in the Bertrand sense, may be associated to higher industry concentration and lower collective welfare than "soft" price competition in the Cournot sense.

The main objective of this paper is to analyze the links between product market competition, innovation and growth. We capture the idea that firms innovate in order to try to escape -albeit temporarily - from the pressure of competition exerted on them by their rivals. There are two ways in which competitive pressure can be thought of as a driving force to innovate. In leveled industries where all the firms have access to the same technological knowledge, the greater is the intensity of competition between the neck by neck firms the lower will be their current profits. Thus, as the competitive pressure increases, these firms will devote a higher ft&D effort to obtain a leadership and escape from the unprofitable state. In unleveled industries, where one firm has obtained a technological lead, the greater is the intensity of competition, the lower will be the current profit of the laggard firm. This should increase the incentive of this firm to eliminate its disadvantage by catching-up or leapfrogging the current leader. We assume that if a laggard firm succeeds in innovating, it will either leapfrog the leader with some probability or catch-up its technology with the complementary probability. The dynamics of industry are thus more complex than in pure leapfrogging models. By using a quadratic R&D cost function, we investigate how innovation and growth are affected in the stationary state by the intensity of competition and by the probability of leapfrogging.

Many commodity markets satisfy the assumptions that underlie the Cournot model. These markets, however, have a feature that is not considered in that model - producers and consumers can enter into contracts for forward transactions. We consider the implications of forward trading for Cournot markets. In particular, we take the simple two-period game that is common in the literature and extend it to include various sorts of adjustment costs. The adjustment costs that we consider are of two sorts : They can involve time or periods during which players are committed to their decisions, or they can involve dollars or expenditure of resources when those decisions are changed. Whereas the former are procompetitive or output enhancing, we show that, in general, the latter are anticompetitive or output restricting.

For a long time, the analysis of the Compatibility of firm strategies with the rules of Competition Law was the Lawyers private domain. It can't be denied, however that the interest some economists have more lately shown in this field, has greatly helped to improve some juridical decisions. The Game Theory for instance has definitely been helpful in the detection of collusive situations, as indeed the Theory of Contestable Markets when dealing with merging projects.dominant positions, and industries newly opened to competition. Similarly the economists have largely contributed to the working out of the new competition law regulations. The latest legal framework concerning vertical agreements for instance, as well as the leading decision of the Commission make clear reference to the Agency and Transaction Costs theories. Besides, in its appraisal of R&D agreements, the Commission seems to make use of the production theory.

This paper is devoted to the study of the price formation in a context of general equilibrium. In fact, I try to understand how the works on imperfect competition improve this field. This is why I progressively review the contributions of the standard monopoly theory, of the monopolistic competition approach and of the standard general equilibrium theory. Several models are presented in this paper in which I progressively increase the degree of rationality of price maker by moving from a subjective to an objective perception of the demand. In each case, I also briefly discuss the existence conditions.

Notes on Strategic Market Games One briefly presents strategic market games à la Shapley and Shubik (1977) within exchange economies. Their properties are compared with the usual ones of Walrasian equilibrium in perfect competition. One examines whether this kind of models can be a framework to study imperfect competition in general equilibrium.

Classical and Keynesian Features in Macroeconomic Models of Imperfect Competition For more than fifty years now the two main (and competing) paradigms in macroeconomics have been the classical and Keynesian ones. Since about twenty five years a new paradigm, imperfect competition macroeconomics, has emerged, which avoids the main shortcomings of the two earlier ones. We investigate in this article whether the models in this line of work have more Keynesian or classical properties. For that purpose we construct a simple prototype macroeconomic model with imperfect competition and rational expectations, and study its properties. We find notably that the equilibria of this model have inefficiency properties very similar to those of Keynesian models. The economy, however, reacts to monetary and fiscal policies in a very " classical " manner. Finally normative prescriptions are neither Keynesian nor classical.

This paper evaluates the implications of imperfect competition for macroeconomics. The paper is organized around three sources of shocks : technology, government spending and money. For each, we summarize existing theories and present quantitative evidence on the effects of imperfect competition.