What is a public good? A public good is something that is both non-excludable in provision and non-rivalrous in consumption. That is, a public good is a good the suppliers of which cannot keep additional people from consuming once it is supplied and can be consumed by additional consumers without diminishing the quantity supplied.
Boiled down, it amounts to this: public goods are those goods individuals might be unwilling to provide because charging per head is too difficult. Consumers can sneak some on the sly without leaving any incriminating evidence, or at least what evidence they might leave is difficult to detect without the producer spending a lot of money.
Whether or not something is a public good is not a function of whether or not it is provided by government. People provide public goods all the time, sometimes not even knowing that they do. Each time I tidy up my landscaping and mow my lawn, passersby and neighbors get to enjoy it free of charge. There is no way feasible to me to charge people for exploiting the aesthetic value I provide. Furthermore, my bushes don’t wilt, nor does my grass turn brown if the number of people enjoying the pastoral beauty of my front lawn increases to a steady stream of cars, bikes and chartered buses.
Radio broadcasts are another public good. There is no cost-effective way for a radio station to hunt down people who listen without paying, and the number of listeners can increase without the radio signal breaking down.
Public roads are one example of a public good provided by governments. Once they are built, there is no way to keep people who have not financed them from using them. Municipalities overcome this problem by taxing their citizens to pay for them. Public roads are non-rivalrous enough until traffic increases. Could roads be provided by private entities? Yes—they would operate as toll roads. Governments already operate toll roads to more accurately reflect the cost of their use.
National defense is commonly used as an example of a public good, even though it is not entirely clear that it is. Once an army is established and charged with defending a particular area, it is difficult to make sure all the people in that area pay for whatever portion of defense they enjoy. Like public roads, defense is non-rivalrous to a point. Increases in territory or population can make consuming defense difficult.
What are public schools? Are they a public good?
I think the more important question to ask, given the definition I provided at the outset, is “Is education a public good?” Most people would agree that it is, under the belief that a society improves when it has more people who are more educated. Our government leaders have made it a priority to educate as many people as possible, and they have tried to make sure each person receives the highest amount of education possible.
Is this the right way to look at it? I don’t think so. Educating someone may not be a public good, because it is never up to the educator how well the educated uses her new knowledge. Educating someone is not as simple as fertilizing your lawn once a year and keeping the boxwoods tidy. Your lawn won’t drop out of college to sit in a coffee shop and read Proust for a year, and your boxwoods aren’t going to take up with the wrong crowd. In fact, in a world of relative individual freedom and relatively limited government, educating someone so that they use that education exactly as you intended is impossible.
Suppliers of education in the public school system can exclude certain consumers through assessment tests and course plans designed for “gifted” students. A teacher can give a student just that amount of education he deems necessary. A school district can restrict access to reading materials in schools, and local governments can ban books outright.
Consumers of education in the public school system can certainly diminish the quantity—and quality—of education supplied by crowding classrooms.
Perhaps education is not a public good. Is learning? I think learning is. Learning something on one’s own, or allowing oneself to be taught, come closer to the definition of public goods. Just as I don’t mow my lawn for my neighbor’s benefit but they benefit nevertheless, I educate myself for no one’s benefit but my own, and yet my increased understanding has positive spillover effects for others. I may become more circumspect in my criticism of others, or I may become a better manager once understanding opportunity cost. If I keep my mental landscape tidy, I will have no choice but to benefit others, even though I do so only for my own benefit.