The first category is pure public goods, which are both non-exclusive and non-competitive; The second kind of public goods is characterized by non-competitive consumption, but it can easily be exclusive. Some scholars call this kind of goods club goods. The third kind of public goods is just the opposite of club products, that is, they are competitive in consumption, but they cannot be effectively excluded. Some scholars call this kind of goods * * * public resources or public * * * pond resources. Club goods and goods with the same resources are generally called "quasi-public goods", that is, they are not exclusive and non-competitive at the same time. Quasi-public goods generally have the characteristics of "crowding", that is, when the number of consumers increases to a certain value, the marginal cost will be positive, instead of increasing one's consumption like pure public goods, and the marginal cost will be zero. After the quasi-public goods reach the "crowded point", each additional person will reduce the utility of the original consumers. The classification of public goods and the "crowded" characteristics of quasi-public goods provide a theoretical basis for us to explore the multiplicity of public goods.

In addition, public goods can also be classified as follows:

(1) Pure public goods: completely non-competitive and non-exclusive, such as national defense and lighthouses, which are usually provided free of charge. It is rare in real life.

(2) Quasi-public goods: limited non-competitiveness and partial exclusivity. That is, beyond a certain critical point, non-competitiveness and non-exclusivity will disappear and congestion will appear. Quasi-public goods can be divided into two categories:

A. public goods. For example, compulsory education, public libraries, museums and parks.

B public goods, also known as natural monopoly products. Such as telecommunications, electricity, tap water, pipelines, gas, etc.