Heioo: New encyclopedia entry on General Equilibrium

2026-10-06T05:43:08Z

New encyclopedia entry on General Equilibrium

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'''General equilibrium''' theory analyses the simultaneous determination of prices and quantities in all markets of an economy, taking account of the interdependence among markets. In contrast to partial equilibrium analysis, which studies a single market in isolation, general equilibrium analysis recognises that changes in one market affect conditions in others, and that a consistent outcome requires that all markets clear at once.

== Walrasian Foundations ==
The modern theory originates with Leon Walras, who modelled an economy as a system of interdependent markets and sought the conditions under which a set of prices exists that equates supply and demand in every market. The concept of the tâtonnement, a hypothetical process of price adjustment, was introduced to describe how equilibrium might be reached, though it abstracts from actual trading and production during adjustment.

The existence of a general equilibrium was proved rigorously in the twentieth century under assumptions of convex preferences and production sets, continuous demand, and appropriate boundary conditions. The proofs are existence results: they establish that a price vector clearing all markets exists, without specifying how it might be found.

== Welfare Theorems ==
Two fundamental theorems link general equilibrium to welfare. The first states that a competitive equilibrium, under specified conditions, is Pareto efficient: no reallocation can make someone better off without making someone else worse off. The second states that, under suitable conditions, any Pareto-efficient allocation can be achieved as a competitive equilibrium with an appropriate distribution of initial endowments and lump-sum transfers.

These theorems provide a benchmark for evaluating market outcomes and the case for intervention. They also clarify that efficiency and distribution are distinct issues: the market determines efficiency given endowments, while distribution depends on the initial allocation of resources and on the tax and transfer system.

== Uniqueness and Stability ==
Existence does not guarantee uniqueness or stability. Multiple equilibria can arise, particularly when there are increasing returns or complementarities, and equilibrium may be unstable under plausible adjustment processes. The Sonnenschein-Mantel-Debreu theorem shows that aggregate excess demand functions are not restricted to forms that guarantee uniqueness or stability, undermining attempts to derive general results about market economies from individual rationality alone.

When equilibria are multiple, the selection of equilibrium and the design of policy become more complex, because expectations and coordination matter. This has motivated research on equilibrium selection, on the role of institutions, and on the conditions under which the competitive outcome is well-behaved.

== Computation and Applications ==
General equilibrium models are widely used in applied economics to evaluate the effects of tax policy, trade liberalisation, and environmental regulation. Computable general equilibrium models specify production technologies, consumer preferences, and market structure, and solve numerically for the counterfactual equilibrium. These models are used by governments and international organisations to assess policy proposals, though their results depend on the assumed parameters and structure.

== Criticisms and Extensions ==
Criticisms of general equilibrium theory concern its assumptions of complete markets, perfect competition, and full information, and its abstraction from money, time, and uncertainty. Extensions incorporate incomplete markets, imperfect competition, and dynamic optimisation, but at the cost of tractability and generality. Despite these limitations, the framework remains the organising structure of much of economic theory.

== Core versus Extended Models ==
A distinction is drawn between core general equilibrium models and extended versions. Core models assume complete markets, perfect competition, and full information, and yield sharp results such as the welfare theorems. Extended models relax these assumptions to accommodate incomplete markets, imperfect competition, externalities, and asymmetric information.

Each extension changes the conclusions. With incomplete markets, equilibria are generally not Pareto efficient, and the scope for intervention widens. With imperfect competition, prices exceed marginal cost, and the welfare theorems no longer apply. The progression from core to extended models reflects the effort to make the framework more realistic while retaining its analytical structure.

== Money in General Equilibrium ==
Incorporating money into general equilibrium has proved difficult, because in a complete-markets setting there is no need for a medium of exchange: all trades can be executed simultaneously at the equilibrium prices. Money must therefore be introduced through frictions, such as cash-in-advance constraints, money in the utility function, or search and matching in exchange.

These approaches generate different implications for the role of money and for the effects of monetary policy. The difficulty of modelling money reflects a deeper tension between the general equilibrium framework and the features of real economies in which money and financial institutions are central.

== Dynamics and Growth ==
Dynamic general equilibrium models extend the framework over time, incorporating capital accumulation, saving, and intertemporal optimisation. The Ramsey model and overlapping generations models are the principal examples. These models are used to analyse growth, taxation, and the effects of policy on long-run outcomes.

Modern dynamic stochastic general equilibrium models add uncertainty and are the workhorse of policy analysis in central banks and international organisations. They combine microfoundations with aggregate dynamics, though their assumptions and their ability to match the data have been debated.

== Critiques from Outside ==
Critics from heterodox traditions question the emphasis on equilibrium, the treatment of time and uncertainty, and the neglect of institutions and power. Post-Keynesian and institutionalist economists argue that economies are not systems tending toward equilibrium but processes of change in which history and institutions matter.

Defenders of the framework acknowledge its limitations but argue that it provides a disciplined way of organising thought, that its assumptions are transparent and can be varied, and that its results clarify the conditions under which markets perform well. The debate about the framework is in part a debate about the appropriate goals and methods of economic theory.

== See also ==
* [[Partial Equilibrium]]
* [[Pareto Optimum]]
* [[Welfare economics]]

== References ==

<ref name="r1">Walras, L. Elements of Pure Economics.</ref>
<ref name="r2">Research on the existence and stability of general equilibrium.</ref>
<ref name="r3">Studies of computable general equilibrium models.</ref>

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[[Category:Microeconomics]]
[[Category:Welfare economics]]
[[Category:Econometrics]]

General Equilibrium - Revision history

Heioo: New encyclopedia entry on General Equilibrium