AP Microeconomics / Market Failure and the Role of Government
Lesson
Public goods and the equity conversation
Some goods are hard to sell in a private market. Other policies change the distribution of income.
Learning goals
- Classify a good using rivalry and excludability.
- Distinguish an efficiency argument from an inequality argument.
Explanation
A public good is nonrival—one person’s use does not use it up—and nonexcludable—people who do not pay are hard to keep out. National defense is the usual classroom case. Private sellers struggle because free riders hope someone else will pay. That is a market-failure story, not a claim that government provision is automatically cheap.
Inequality is a different question. Markets can be efficient and still leave very unequal incomes. Taxes, transfers, and public services change the distribution. Keep the two conversations labeled: one is about wasted trades, the other is about who has what.
Key terms
- Public good. A good that is nonrival and nonexcludable.
- Free rider. A person who enjoys a good without paying because exclusion is difficult.
Common mistakes
- Calling a city park a public good when it can become rival on a crowded day.
- Using “market failure” as a synonym for “I dislike the outcome.”
Practice
Original Marlow Works items. Check the answer explanation after you try.
A binding price ceiling is set below equilibrium in the market for rental apartments. What is the most likely result?
Original Marlow Works item — not a College Board question.
Take your time—this is practice, not a test.
Answer explanation
Why is a sandwich not a public good?
Answer. It is both rival and excludable: one person eating it prevents another, and a seller can require payment.
Public goods fail those two tests at once.
Related resources
External links with reuse status. Marlow Works is independent and does not copy restricted exam or textbook material.
Official / link only
AP Microeconomics course page
Official six-unit framework for markets, costs, and market failure.
College Board · All rights reserved · accessed 2026-10-01
Open sourceCC BY — attribution required
Principles of Microeconomics: Scarcity and Social Provisioning
Open microeconomics background for scarcity, markets, and elasticity.
Open Textbook Library listing · CC BY · accessed 2026-10-01
Open source