The price system is an extraordinarily powerful instrument in organizing an economic system, but it is subject to three broad classes of limitations.

Sometimes prices are not permitted to do their work. Monopolies are able to exert control over prices, and they use it, sensibly enough, to raise their profits above the level allowed by competition. The monopolist (or group of colluding enterprises) sets prices at a level such that prices are above costs or, to use words of identical significance, such that resources earn more in the monopolized industry than they can earn elsewhere. The basis of the monopoly is its ability to prevent outsiders from entering the industry to share in the unusual profits and, by the act of producing, actually serve to eliminate them.

The fixing of prices by monopolists reduces the income of society. This is, in fact, the only well-established criticism (on grounds of efficiency) to be levied against monopolies; there is no reason to assume that they will make products less-suited to consumer tastes or innovate more slowly or pay lower wages or otherwise misallocate resources. But the basic inefficiency led, first in the United States in 1890 and then increasingly in European nations, to governmental policies to maintain or restore competition.

Public price control has two aspects. A large part of public regulation is intended to correct monopolistic pricing (or other failures of the price system); this includes most public-utility regulation in the United States (transportation, electricity, gas, etc.). Whatever the success of these endeavours—and on the whole there has been a substantial decline in confidence in the regulatory bodies—they are usually instructed to achieve the goals of an efficient price system.

Other public price controls are designed to serve ends outside the reach of the price system. Prices of farm products are regulated (raised) in most nations with the intention of improving farmers’ incomes, and the fixing of interest rates paid by banks is undertaken to improve bank earnings. Such policies are invariably defended on various economic and ethical grounds but reflect primarily the political strength of large and well-organized producer groups.

Even when prices are freely established by competition, there is a class of economic relationships called “externalities” not efficiently controlled by prices. These may be illustrated by the air pollution caused by automobiles. Since no single automobile makes a significant contribution to air pollution, the owner has no incentive to bear the cost of installing antipollution devices even though all drivers would be better off if each did so. Yet if there are many automobiles in a region, it would be prohibitively expensive for drivers to contract with one another to have each install devices in his automobile to reduce pollution. The external effects of any one automobile’s exhaust fumes are so diffuse and affect any one person so triflingly that they cannot be regulated by the price system.

The class of “externalities” is as broad as the class of actions that have effects upon people who are not parties to the contracts governing the actions. An attractive garden pleases passers-by, but they cannot be charged a portion of its cost. A new piece of scientific knowledge will prove useful to unknown persons. These two examples indicate that some externalities are economically trivial and some are highly important.

When the price system cannot deal with diffused effects, other social controls often take its place. The state invokes a whole arsenal of policies to deal with externalities, of which the following are only examples: (1) The state may subsidize activities that do not end in a product that can be sold. Thus, basic scientific research that does not lead to patentable processes is subsidized. (2) Individuals may be compelled to act uniformly in areas where contracts would be too expensive; traffic laws, zoning laws, and compulsory vaccination are examples. (3) The state may itself undertake an activity that cannot be financed by sale of services, the most obvious example being national defense.

An interesting type of externality is the problem of highway congestion. Any one person’s presence on a highway at a time and place of peak density has only a negligible effect upon others, so that, except on toll roads, private contracts have not been feasible. The state itself has not been able to deal effectively with highway congestion. More highways can be built until no highway is ever crowded, but this would be intolerably expensive. The state has lacked a method of inducing drivers to shift to less-crowded hours and routes by charging fees to those drivers who impose high congestion costs by driving at peak times. Recent developments in technology may make it feasible to use the price system to reduce congestion. For example, cameras at appropriate points could photograph automobile licenses, and a computer could accumulate the charges on the basis of route and time for each automobile. Then only a person for whom travel at peak times was worth, for example, 25 cents per mile would impose (and pay for) the congestion he created.