Public Good vs Common-Pool Resource
Public Good and Common-Pool Resource are related 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, common-pool resource is a common-pool resource is rival but non-excludable — one person's use reduces what's left, but it's hard to stop anyone from using it. 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 common-pool resource is rival but non-excludable — one person's use reduces what's left, but it's hard to stop anyone from using it.
Fisheries, forests, and groundwater are examples. Because users can't be excluded, they tend to be overused (the tragedy of the commons). Solutions include quotas, property rights, and community management.
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