Tragedy of the commons

The tragedy of the commons is a metaphoric label for a concept that is widely discussed in economics, ecology and other sciences. According to the concept, should a number of people enjoy unfettered access to a finite, valuable resource such as a pasture, they will tend to over-use it, and may end up destroying its value altogether. To exercise voluntary restraint is not a rational choice for individuals – if they did, the other users would merely supplant them – yet the predictable result is a tragedy for all.

The metaphor is the title of a 1968 essay by ecologist Garrett Hardin. As another example he cited a watercourse which all are free to pollute. But the principal concern of his essay was overpopulation of the planet. To prevent the inevitable tragedy (he argued) it was necessary to reject the principle (supposedly enshrined in the Universal Declaration of Human Rights) according to which every family has a right to choose the number of its offspring, and to replace it by "mutual coercion, mutually agreed upon".

The concept itself did not originate with Hardin, but extends back to classical antiquity, being discussed by Aristotle. Some scholars have argued that over-exploitation of the common resource is by no means inevitable, since the individuals concerned may be able to achieve mutual restraint by consensus. Others have contended that the metaphor is inapposite because its exemplar - unfettered access to common land - did not exist historically, the right to exploit common land being controlled by law.