Excludability in the context of Richard Musgrave (economist)

In philosophy, economics, and political science, the common good (also commonwealth, common weal, general welfare, or public benefit) is either what is shared and beneficial for all or most members of a given community, or alternatively, what is achieved by citizenship, collective action, and active participation in the realm of politics and public service. The concept of the common good differs significantly among philosophical doctrines. Early conceptions of the common good were set out by Ancient Greek philosophers, including Aristotle and Plato. One understanding of the common good rooted in Aristotle's philosophy remains in common usage today, referring to what one contemporary scholar calls the "good proper to, and attainable only by, the community, yet individually shared by its members."

The concept of common good developed through the work of political theorists, moral philosophers, and public economists, including Thomas Aquinas, Niccolò Machiavelli, John Locke, Jean-Jacques Rousseau, James Madison, Adam Smith, Karl Marx, John Stuart Mill, John Maynard Keynes, John Rawls, and many other thinkers. In contemporary economic theory, a common good is any good which is rivalrous yet non-excludable, while the common good, by contrast, arises in the subfield of welfare economics and refers to the outcome of a social welfare function. Such a social welfare function, in turn, would be rooted in a moral theory of the good (such as utilitarianism). Social choice theory aims to understand processes by which the common good may or may not be realized in societies through the study of collective decision rules. Public choice theory applies microeconomic methodology to the study of political science in order to explain how private interests affect political activities and outcomes.

In economics, a public good (also referred to as a social good or collective good) is a commodity, product or service that is both non-excludable and non-rivalrous and which is typically provided by a government and paid for through taxation. Use by one person neither prevents access by other people, nor does it reduce availability to others, so the good can be used simultaneously by more than one person. This is in contrast to a common good, such as wild fish stocks in the ocean, which is non-excludable but rivalrous to a certain degree. If too many fish were harvested, the stocks would deplete, limiting the access of fish for others. A public good must be valuable to more than one user, otherwise, its simultaneous availability to more than one person would be economically irrelevant.

Capital goods may be used to produce public goods or services that are "...typically provided on a large scale to many consumers." Similarly, using capital goods to produce public goods may result in the creation of new capital goods. In some cases, public goods or services are considered "...insufficiently profitable to be provided by the private sector.... (and), in the absence of government provision, these goods or services would be produced in relatively small quantities or, perhaps, not at all."

Common goods (also called common-pool resources) are defined in economics as goods that are rivalrous and non-excludable. Thus, they constitute one of the four main types based on the criteria:

• whether the consumption of a good by one person precludes its consumption by another person (rivalrousness)
• whether it is possible to prevent people (consumers) who have not paid for it from having access to it (excludability)

As common goods are accessible by everybody, they are at risk of being subject to overexploitation which leads to diminished availability if people act to serve their own self-interests.

In economics, a good is said to be rivalrous or a rival if its consumption by one consumer prevents simultaneous consumption by other consumers, or if consumption by one party reduces the ability of another party to consume it. A good is considered non-rivalrous or non-rival if, for any level of production, the cost of providing it to a marginal (additional) individual is zero. A good is anti-rivalrous and inclusive if each person benefits more when other people consume it.

A good can be placed along a continuum from rivalrous through non-rivalrous to anti-rivalrous. The distinction between rivalrous and non-rivalrous is sometimes referred to as jointness of supply or subtractable or non-subtractable. Economist Paul Samuelson made the distinction between private and public goods in 1954 by introducing the concept of nonrival consumption. Economist Richard Musgrave followed on and added rivalry and excludability as criteria for defining consumption goods in 1959 and 1969.  

A private good is defined in economics as "an item that yields positive benefits to people" that is excludable, i.e. its owners can exercise private property rights, preventing those who have not paid for it from using the good or consuming its benefits; and rivalrous, i.e. consumption by one necessarily prevents that of another. A private good, as an economic resource is scarce, which can cause competition for it. The market demand curve for a private good is a horizontal summation of individual demand curves.

Unlike public goods, such as clean air or national defense, private goods are less likely to have the free rider problem, in which a person benefits from a public good without contributing towards it. Assuming a private good is valued positively by everyone, the efficiency of obtaining the good is obstructed by its rivalry; that is simultaneous consumption of a rivalrous good is theoretically impossible. The feasibility of obtaining the good is made difficult by its excludability, which means that people have to pay for it to enjoy its benefits.