Public goods have two basic characteristics: one is government investment; The other is non-exclusivity, that is, one person's use of the product does not hinder others' use, such as national defense, public security, justice and so on. And, of course, compulsory education that we are concerned about.

Although higher education is also a government investment, it is an exclusive service. That is, the number of service places it provides is limited. If one person enjoys it, there must be another person who cannot enjoy it. This kind of exclusivity did not come into being after colleges and universities charged tuition fees, but existed in the era of free, and the degree of exclusivity was higher. Therefore, higher education has never been a pure public product, but can only be regarded as a "quasi-public product", just like airports and docks are all funded by the government, but not everyone can use them for free.