Which of the following most directly internalizes externalities?

• A. Pigovian taxes or subsidies that align private costs with social costs
• B. Tariffs
• C. Quotas
• D. Price controls

Answer: (A)

Internalizing externalities means getting private decisions to reflect societal costs or benefits. When there’s a negative externality like pollution, the private cost is too low relative to the social cost. A Pigovian tax on pollution raises private costs by exactly the marginal external cost, nudging firms to pollute less and move toward the socially optimal quantity. A subsidy works in the opposite direction for positive externalities, raising private incentives so the private benefit lines up with the social benefit. These taxes or subsidies directly align private incentives with social welfare.

Tariffs and quotas change who can produce or trade and how much is bought, but they don’t address the underlying external costs or benefits to third parties. Price controls distort prices and allocations but don’t internalize the external effects.