How can a public-good benefit reach someone who does not contribute?

A public good has two defining properties. It is nonexcludable when preventing others from benefiting is difficult or costly, and nonrival when one person’s use does not reduce another’s use. These properties can allow someone to benefit from provision without contributing to its cost.

The invented two-person model makes that connection explicit. Each contribution costs its contributor three points and gives two benefit points to both A and B. The benefit reaches both regardless of who paid, and either person’s benefit does not reduce the other’s. Additional contributions add benefits under the stated rule.

A net payoff is received benefit minus a person’s own contribution cost. If both contribute, each receives four benefit points and pays three, leaving one each. If only A contributes, A receives two minus three, or negative one, while B receives two without paying. With neither contribution, both net payoffs are zero.

Holding the other person’s choice fixed, withholding one’s own contribution raises the displayed personal payoff by one point. Yet both contributing produces a combined net payoff of two, compared with zero when neither contributes. This is a conditional free-rider incentive: benefiting from another’s contribution while avoiding one’s own cost can conflict with the combined point total.

Actual behavior need not follow a points-only calculation. People may value other outcomes or use different institutions. The table explains one incentive structure, not a universal prediction or a recommendation for how public goods should be funded.