public goods

private goods are

rivalrous and excludable

public goods are

non-rivalrous and non-excludable

rivalrous goods

consumption by one person results in the good not being available for consumption by another

excludable goods

once provided, it is possible to prevent others from using it e.g. memberships and subscriptions

public goods have

zero marginal cost

free rider problem

- when someone receives the benefit but allows others to pay for it

missing markets for public goods occur because

there is little incentive to pay for the consumption of the good because you can receive its benefits without paying

quasi-public goods

semi non-rivalrous and semi non-excludable

why are quasi public goods semi non-rivalrous?

because up to a point, more consumers consuming it doesn't reduce the space for others

why are quasi public goods semi non-excludable?

because it is possible but difficult/expensive to exclude non-paying customers e.g. fencing a park