General equilibrium theory
General equilibrium theory is a mathematical framework in economics that analyzes the simultaneous interactions of supply, demand, and prices across all markets in an economy to determine a state where no agent can improve their welfare by unilateral action, assuming perfect competition, rational agents, and complete markets. Originating with Léon Walras's Éléments d'économie politique pure in 1874, the theory posits that an economy can reach a configuration where aggregate excess demands are zero at some price vector, with agents maximizing utility subject to budget constraints.[1]
Key developments include the Arrow-Debreu model of 1954, which extended Walrasian ideas to incorporate production, time, and uncertainty through contingent commodities, proving the existence of competitive equilibria under convexity assumptions via fixed-point theorems like Brouwer's or Kakutani's. This model supports the first fundamental theorem of welfare economics, stating that every competitive equilibrium allocation is Pareto efficient, and the second theorem, asserting that any Pareto efficient allocation can be decentralized as a competitive equilibrium with suitable initial endowments or transfers. These results provide a theoretical justification for markets as mechanisms for efficient resource allocation absent externalities or market failures.[1]
Despite its foundational role, general equilibrium theory has notable limitations and controversies, particularly the Sonnenschein-Mantel-Debreu (SMD) theorem from the 1970s, which demonstrates that aggregate excess demand functions satisfy only weak properties—homogeneity, Walras' law, and continuity—implying virtually any such function can arise from optimizing individual behaviors, thus precluding unique equilibria or strong comparative statics predictions.[2] This indeterminacy undermines the theory's empirical testability and predictive power, as real economies exhibit path dependence, frictions, and disequilibria not captured by static models.[2] Empirical applications remain challenging, with validations often relying on computable general equilibrium models for policy simulations rather than direct falsification, highlighting a disconnect between the theory's mathematical rigor and observable market dynamics.[3]