Which of the following are properties of a public good?

• A. Excludable and Rival
• B. Excludable and Non-rival
• C. Non-excludable and Non-rival
• D. Non-excludable and Rival

Answer: (C)

Public goods have two key traits: non-excludable and non-rival. Non-excludable means you can’t prevent people from using the good, even if they don’t pay. Non-rival means one person’s use doesn’t reduce another person’s ability to use it. Because of this, once provided, everyone benefits and it’s hard to charge people individually, which leads to the free-rider problem and often under-provision by markets. So a good described as non-excludable and non-rival fits the idea of a public good. The other combinations describe private, club, or common-resource goods, which aren’t public goods.