Public Good vs Private Good
Public Good and Private Good are two Market Failure & Government concepts in AP Economics that students often mix up. In short: public good is a public good is non-excludable and non-rival: no one can be excluded from it, and one person's use does not reduce another's. Meanwhile, private good is a private good is both excludable and rival: people can be prevented from using it, and one person's use reduces what is left for others. Here is how they compare side by side.
A public good is non-excludable and non-rival: no one can be excluded from it, and one person's use does not reduce another's.
National defense and street lighting are classic examples. Because users cannot be excluded, markets underprovide public goods due to the free-rider problem. They are usually funded by government through taxation.
A private good is both excludable and rival: people can be prevented from using it, and one person's use reduces what is left for others.
Most goods, such as food and clothing, are private goods. Markets generally provide them efficiently because sellers can charge a price and exclude non-payers. They contrast with public goods, which are non-excludable and non-rival.