Partial Equilibrium vs General Equilibrium
Partial Equilibrium and General Equilibrium are two Microeconomic Theory concepts in AP Economics that students often mix up. Partial equilibrium is the analysis of a single market on its own, holding prices and conditions in all other markets constant. General equilibrium is a state in which every market in the economy clears at once, with all prices adjusted so supply equals demand everywhere. Here is how they compare side by side.
Partial equilibrium is the standard supply and demand diagram: one market, one price, everything outside the diagram frozen. The ceteris paribus assumption is doing the work, since income, other prices, and technology are all held still while the market in question finds its clearing price. This is a good approximation when the market is small enough that its spillovers barely move anything else, which covers most exam questions about a tax, a price ceiling, or a shift in demand. It breaks down for large markets or big shocks, where feedback from other markets changes the answer. General equilibrium is the alternative that lets every price move at once, at the cost of a much larger model.
General equilibrium analysis treats the economy as one connected system: prices in every market adjust together until quantity supplied equals quantity demanded in all of them simultaneously. It takes seriously that markets feed back on each other, so a shock to the oil market changes wages, the demand for cars, and the price of plastics, which then feed back into oil. The payoff is consistency, because the answer accounts for every knock-on effect instead of stopping at the first market. The cost is complexity, since solving a general equilibrium model needs assumptions about every market and every consumer. Partial equilibrium is the simpler alternative that studies one market with everything else held constant, which is usually accurate enough when the market is small relative to the economy.
Partial Equilibrium vs General Equilibrium: One Market at a Time or All of Them at Once
| Partial Equilibrium | General Equilibrium | |
|---|---|---|
| Scope of the question | A single market examined on its own | Every market in the economy at the same time |
| What is held constant | Prices and incomes everywhere else | Nothing; all prices adjust together |
| Usual tool | One supply and demand diagram | A system of equations, or an Edgeworth box in the two good case |
| Feedback from other markets | Assumed away | Traced through, including effects that loop back to the first market |
| When it works well | Small markets with weak links to the rest of the economy | Large sectors, or shocks that hit many markets at once |
| Strongest conclusion available | How surplus changed in this one market | Whether the whole allocation of resources is efficient |
A tax question shows exactly how far one diagram will carry you
Take a market where quantity demanded is 90 minus 3 times the price and quantity supplied is 10 plus 2 times the price. Setting the two equal gives 80 equals 5 times the price, so the price is 16 and the quantity is 42. Now impose a tax of 5 dollars a unit collected from sellers. Supply becomes 10 plus 2 times the price minus 5, which simplifies to 2 times the price. Setting 90 minus 3 times the price equal to 2 times the price gives a price of 18 and a quantity of 36. Buyers now pay 18, up by 2, sellers keep 13, down by 3, and the government collects 5 times 36, or 180 dollars. That is a complete partial equilibrium answer and it is correct as far as it goes. What it assumed is enormous: that no other price in the economy moved. The workers who lost hours in this industry were assumed to have no effect on wages elsewhere, and the buyers who cut back were assumed to spend the difference nowhere in particular. See /micro/supply-and-demand for the underlying diagram. The numbers are illustrative.
General equilibrium exists because the assumed away effects sometimes dominate
Follow the money the partial answer dropped. Buyers who cut back on the taxed good spend that income somewhere else, raising demand in substitute markets and pushing those prices up, which feeds back and softens the fall in demand for the taxed good. Producers who scale back release labor and capital, which flows to other industries and nudges input prices down, shifting supply curves across the economy. General equilibrium analysis keeps all of these adjusting at once and asks for the set of prices at which every market clears simultaneously. The payoff is that questions a single diagram cannot even state become answerable, such as whether the final allocation of resources is efficient in the sense that nobody could be made better off without harming someone. The cost is complexity, which is why introductory courses stay with one market and treat everything else as a background assumption. The two good version is manageable by hand and is drawn in an Edgeworth box, where trade between two people continues until no further mutual gain exists. See /glossary/edgeworth-box for that construction.
Frequently asked questions
What is the difference between partial and general equilibrium?
Partial equilibrium studies one market by itself while holding conditions in all other markets fixed, and general equilibrium solves every market at once so that all prices adjust together. The first gives a fast answer for one market and the second accounts for the feedback the first ignores.
Which one do introductory economics courses use?
Almost always partial equilibrium, because a single supply and demand diagram is a partial equilibrium model. General equilibrium normally appears later, in the form of the Edgeworth box or the production possibilities frontier.
Why can partial equilibrium give a misleading answer?
Because it treats effects that spill into other markets as if they did not exist, and those spillovers can loop back and change the original market. A policy that looks small in one diagram can shift wages, input prices or demand for substitutes enough to alter the result.
Live Supply and Demand graph. Drag the curves, or open the full version.
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