コースの定理

The Coase Theorem states that costless negotiation among market participants leads to an efficient outcome regardless of who holds legal property rights. When a factory creates noise pollution affecting a nearby homeowner, either party can negotiate a solution. If the homeowner values silence at $10,000 and noise control costs $8,000, the efficient outcome—installing controls—occurs whether the factory or homeowner holds the right, though the distribution of benefits differs.

Property rights determine which party bears the economic burden but not the final efficient outcome. If the factory holds pollution rights, the homeowner pays $8,000 for controls. If the homeowner holds silence rights, the factory installs controls at its own cost. In both cases, controls are installed, but the distribution of costs and benefits reverses based on who holds the property rights.

The Coase Theorem requires well-defined and enforceable property rights, negligible transaction costs, symmetrical information between parties, and balanced negotiation power. These assumptions ensure both parties can negotiate freely without legal fees, time delays, or information disadvantages. When these conditions exist, private negotiation produces socially efficient resource allocation regardless of initial rights assignment.

Real-world negotiations involve significant transaction costs like legal fees and time delays, unequal bargaining power between parties, and incomplete information. Additionally, parties have incentives to lobby government for favorable rights assignments to avoid economic losses. These practical limitations prevent the theorem's idealized conditions from occurring, making efficient private negotiation outcomes rare in actual markets with externalities.

A crop farmer's pesticide drifts onto a fish farm, causing $12,000 annual damage. Switching to safer pesticide costs $9,000. If the fish farmer holds rights, the crop farmer must use safer pesticide. If the crop farmer holds rights, the fish farmer pays $9,000 compensation to switch. Both scenarios result in safer pesticide use—the efficient outcome—but distribute costs differently between parties.

The Coase Theorem addresses how negative externalities like pollution can be resolved through private negotiation when property rights are assigned. Whether the polluter or victim holds rights, negotiation produces the same efficient outcome if transaction costs are negligible and information is symmetrical. This framework shows that externality problems can be solved through market mechanisms rather than government intervention alone.

The allocation of benefits depends entirely on which party receives the property right. The party holding the right avoids bearing the adjustment cost, while the other party must pay or accept the externality. Although both scenarios achieve the same efficient outcome, the initial rights assignment determines whether the polluter or victim bears the financial burden of resolving the externality.