Splošno ravnotežje je še vedno mrtvo

Frank Ackerman razpravlja o tem, zakaj mrtvorojeni koncept splošnega ravnotežja trdovratno vztraja v ekonomskih modelih, kljub temu, da je bilo jasno dokazano, da ravnotežna točka v ekonomiji ni niti ena sama niti stabilna. Razlog je po njegovem “ideološke” narave: demonstrirati, da se konkurenčno gospodarstvo lahko samouravnava in da ga nevidna roka vedno pripelje v optimalno ravnotežje.

More than 25 years after the discovery that the equilibrium point of a general equilibrium model is not necessarily either unique or stable, there is still a need for an intuitively comprehensible explanation of the reasons for this discovery. Recent accounts identify two causes of the finding of instability: the inherent difficulties of aggregation, and the individualistic model of consumer behaviour. The mathematical dead end reached by general equilibrium analysis is not due to obscure or esoteric aspects of the model, but rather arises from intentional design features, present in neoclassical theory since its beginnings.

In the course of its long decades of rule over the discipline of economics, general equilibrium became established as the fundamental framework for theoretical discourse. Its influence continues to spread in policy applications, with the growing use of computable general equilibrium models. At its peak it even colonized much of macroeconomics, with the insistence on the derivation of rigorous microfoundations for macro models and theories. General equilibrium theory is widely cited in a normative context, often in textbooks or semitechnical discussion, as providing the rigorous theoretical version of Adam Smith’s invisible hand and demonstrating the desirable properties of a competitive economy.

Yet those who follow the news about microeconomic theory have known for some time that general equilibrium is not exactly alive and well any more. The equilibrium in a general equilibrium model is not necessarily either unique or stable, and there are apparently no grounds for dismissing such ill-behaved outcomes as implausible special cases. This conclusion is clearly at odds with established modes of thought about economics; several more `news flashes’ will be required to assimilate and interpret the failure of earlier hopes for general equilibrium models, and to formulate new directions for economic theory.

The second section of this paper presents one such news flash, summarizing and explaining the evidence of fundamental flaws in general equilibrium theory. But simply hearing the news one more time is not enough. The goal of this paper is to develop a basic, intuitively comprehensible understanding of why it happened, as a guide to future theorizing. What features of the general equilibrium model led to its failure? What changes in economic theory are needed to avoid the problem in the future? Section 3 examines contemporary interpretations of the findings of instability. Some attempts have been made to avoid the issue, without success. Despite occasional claims to the contrary, general equilibrium remains fundamental to the theory and practice of economics. Analysts who have faced the problem have identified two underlying causes: the inherent difficulties of the aggregation process, and the unpredictable nature of individual preferences.

Section 4 pursues the roots of the problem in the early history of general equilibrium theory: a mathematical framework transplanted from nineteenth- century physics was far less fruitful in economics, due to fundamental differences between the two fields. The provocative treatment of this topic by Philip Mirowski asks the right questions, but falls short of adequately answering them.

The final section briefly describes alternative approaches that might remedy the earlier flaws in neoclassical theory. Post-general-equilibrium economics will need a new model of consumer behaviour, new mathematical models of social interaction, and an analysis of the exogenous institutional sources of stability.

Vir: Frank Ackerman, Still dead after all these years, Journal of Economic Methodology, 2002

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