Central to Hardin's article is a metaphor of herders sharing a common parcel of land (the commons) on which they are all entitled to let their cows graze. In Hardin's view it is in each herder's interest to put as many cows as possible onto the land even if the commons is damaged as a result. The herder receives all the benefits from the additional cows but the damage to the commons is shared by the entire group. If all herders make this individually rational decision, however, the commons is destroyed and all herders suffer.
Hardin's article has been variously interpreted either as an argument for the privatization of community assets or for increased government regulation.
To make the case for "no technical solutions", Hardin notes the limits placed on the availability of energy (and material resources) on Earth, and also the consequences of these limits for "quality of life". To maximize population, one needs to minimize resources spent on anything other than simple survival, and vice versa. Consequently, he concludes that there is no foreseeable technical solution to increasing both human populations and their standard of living on a finite planet.
From this point, Hardin switches to non-technical or resource management solutions to population and resource problems. As a means of illustrating these, he introduces a hypothetical example of a pasture shared by local herders. The herders are assumed to wish to maximize their yield, and so will increase their herd size whenever possible. The utility of each additional animal has both a positive and negative component:
Crucially, the division of these costs and benefits is unequal: the individual herder gains all of the advantage, but the disadvantage is shared among all herders using the pasture. Consequently, for an individual herder the rational course of action is to continue to add additional animals to his or her herd. However, since all herders reach the same rational conclusion, overgrazing and degradation of the pasture is its long-term fate. Nonetheless, the rational response for an individual remains the same at every stage, since the gain is always greater to each herder than the individual share of the distributed cost. The overgrazing cost here is an example of an externality.
Because this sequence of events follows predictably from the behaviour of the individuals concerned, Hardin describes it as a tragedy.
In the course of his essay, Hardin develops the theme, drawing in examples of latter day "commons", such as the atmosphere, oceans, rivers, fish stocks, national parks, advertising, and even parking meters. The example of fish stocks had led some to call this the "tragedy of the fishers". A major theme running throughout the essay is the growth of human populations, with the Earth's resources being a general commons.
The essay also addresses potential management solutions to commons problems including privatization, polluter pays and regulation. Keeping with his original pasture analogy, Hardin categorises these as effectively the "enclosure" of commons, and notes a historical progression from the use of all resources as commons (unregulated access to all) to systems in which commons are "enclosed" and subject to differing methods of regulated use in which access is prohibited or controlled. Hardin argues against relying on conscience as a means of policing the commons, suggesting that this favours selfish individuals, often known as free riders, over those who are more altruistic.
In the context of avoiding over-exploitation of common resources, Hardin concludes by restating Hegel's maxim (which was actually written by Engels), "liberty is the recognition of want." He suggests that "liberty", completes the tragedy of the commons. By recognising resources as commons in the first place, and by recognising that, as such, they require management, Hardin believes that "we can preserve and nurture other and more precious freedoms."
Aside from its subject matter (resource use), the essay is notable (at least in modern scientific circles) for explicitly dealing with issues of morality, and doing so in one of the scientific community's premier journals, Science. Indeed, the subtitle for the essay is "The population problem has no technical solution; it requires a fundamental extension in morality."
Like William Lloyd and Thomas Malthus before him, Hardin was primarily interested in the problem of human population growth. In his essay he also focused on the use of larger (though still limited) resources such as the Earth's atmosphere and oceans, as well as pointing out the "negative commons" of pollution (i.e., instead of dealing with the deliberate privatisation of a positive resource, a "negative commons" deals with the deliberate commonisation of a negative cost, pollution).
As a metaphor, the tragedy of the commons should not be taken too literally. The phrase is shorthand for a structural relationship and the consequences of that relationship, not a precise description of it. The "tragedy" should not be seen as tragic in the conventional sense, nor must it be taken as condemnation of the processes that are ascribed to it. Similarly, Hardin's use of "commons" has frequently been misunderstood, leading Hardin to later remark that he should have titled his work "The Tragedy of the Unregulated Commons".
The tragedy of the commons has particular relevance in analyzing behaviour in the fields of economics, evolutionary psychology, game theory, politics, taxation, and sociology. Some also see it as an example of emergent behaviour, with the "tragedy" the outcome of individual interactions in a complex system.
More significantly, controversy has been fueled by the "application" of Hardin's ideas to real situations. In particular, some authorities have read Hardin's work as specifically advocating the privatization of commonly owned resources. Consequently, resources that have traditionally been managed communally by local organisations have been enclosed or privatized. Ostensibly, this serves to "protect" such resources, but it ignores the pre-existing management, often appropriating resources and alienating indigenous (and frequently poor) populations. In effect, private or state use may result in worse outcomes than the previous commons management. As Hardin's essay focuses on resources that are fundamentally unmanaged rather than communally managed, this may be a mischaracterisation of his ideas given that Hardin discussed how usage of public property could be controlled in a number of different ways to stop or limit over-usage.
Hardin's advocacy of clearly defined property rights has frequently been misread as an argument for privatization, or private property, per se. The opposite situation to a tragedy of the commons is sometimes referred to as a tragedy of the anticommons: a situation where rational individuals (acting separately) collectively waste a given resource by under-utilizing it.
In practice, related theories have been described by authors throughout history. Thucydides (ca. 460 B.C.-ca. 395 B.C.), for example expressed the concept thus: "[T]hey devote a very small fraction of time to the consideration of any public object, most of it to the prosecution of their own objects. Meanwhile each fancies that no harm will come to his neglect, that it is the business of somebody else to look after this or that for him; and so, by the same notion being entertained by all separately, the common cause imperceptibly decays. Aristotle (384 B.C.-322 B.C.) similarly argued "That all persons call the same thing mine in the sense in which each does so may be a fine thing, but it is impracticable; or if the words are taken in the other sense, such a unity in no way conduces to harmony. And there is another objection to the proposal. For that which is common to the greatest number has the least care bestowed upon it. Every one thinks chiefly of his own, hardly at all of the common interest; and only when he is himself concerned as an individual. For besides other considerations, everybody is more inclined to neglect the duty which he expects another to fulfill; as in families many attendants are often less useful than a few."
More recently, William Forster Lloyd noted the comparison with medieval village land holding in his 1833 book on population.
Such a notion is not merely an abstraction, but its consequences have manifested literally, in such common grounds as Boston Common, where overgrazing required the Common no longer be used as public grazing ground.
Specifically, situations exemplifying the "tragedy of the commons" include the overfishing and destruction of the Grand Banks, the destruction of salmon runs on rivers which have been dammed (most prominently in modern times on the Columbia River in the North West United States, but historically in North Atlantic rivers generally), the devastation of the sturgeon fishery (in modern times especially in Russia, but in historical times in the United States as well), and, in terms of water supply, the limited water available in arid regions (e.g., the area of the Aral Sea) and the Los Angeles water system supply, especially at Mono Lake and Owens Lake.
More general examples (some alluded to by Hardin) of potential and actual tragedies include:
Another solution for certain resources is to convert common good into private property, giving the new owner an incentive to enforce its sustainability. Effectively, this is what took place in the English "Enclosure of the Commons". Increasingly, many agrarian studies scholars advocate studying traditional commons management systems to understand how common resources can be protected without alienating those whose livelihoods depend upon them.
Libertarians and classical liberals often cite the tragedy of the commons as an example of what happens when Lockean property rights to homestead resources are prohibited by a government. These people argue that the solution to the tragedy of the commons is to allow individuals to take over the property rights of a resource, that is, privatizing it. In 1940 Ludwig von Mises wrote concerning the problem:
If land is not owned by anybody, although legal formalism may call it public property, it is used without any regard to the disadvantages resulting. Those who are in a position to appropriate to themselves the returns — lumber and game of the forests, fish of the water areas, and mineral deposits of the subsoil — do not bother about the later effects of their mode of exploitation. For them, erosion of the soil, depletion of the exhaustible resources and other impairments of the future utilization are external costs not entering into their calculation of input and output. They cut down trees without any regard for fresh shoots or reforestation. In hunting and fishing, they do not shrink from methods preventing the repopulation of the hunting and fishing grounds.
Critics of this solution have pointed out that many commons, such as the ozone layer or global fish populations, would be extremely difficult or impossible to privatize.
Psychologist Dennis Fox used a number, what is now termed "Dunbar's number", to take a new look at the tragedy of the commons. In a 1985 paper titled "Psychology, Ideology, Utopia, & the Commons", he stated "Edney (1980, 1981a) also argued that long-term solutions will require, among a number of other approaches, breaking down the commons into smaller segments. He reviewed experimental data showing that cooperative behavior is indeed more common in smaller groups. After estimating that "the upper limit for a simple, self-contained, sustaining, well-functioning commons may be as low as 150 people" (1981a, p. 27).
The Coast Salish managed their natural resources in a place-based system where families were responsible for looking after a place and its resources. Access to food was the major source of wealth and the empowerment of generosity was highly valued so it made sense for them to take care of the resources.
A popular solution to the problem is also the "Coasian" one, where the people using the commons support one another so not to destroy the resource.
In Hardin's essay, he proposed that the solution to the problem of overpopulation must be based on "mutual coercion, mutually agreed upon" and result in "relinquishing the freedom to breed". Hardin discussed this topic further in a 1979 book, Managing the Commons, co-written with John A. Baden. He framed this prescription in terms of needing to restrict the "reproductive right" in order to safeguard all other rights. Only one large country has adopted this policy, the People's Republic of China. In the essay, Hardin had rejected education as an effective means of stemming population growth. Since that time, it has been shown that increased educational and economic opportunities for women correlates well with reduced birthrates in most countries, as does economic growth in general.
The idea has been applied to other areas of sociobiology and behavioral ecology, such as in the evolution of virulence or sexual conflict, where males may fatally harm females when competing for matings. It is also raised as a question in studies of social insects, where scientists wish to understand why insect workers do not undermine the "common good" by laying eggs of their own and causing a breakdown of the society.
The idea of evolutionary suicide, where adaptation at the level of the individual causes the whole species or population to be driven extinct, can be seen as an extreme form of an evolutionary tragedy of the commons.
Commons dilemma researchers have studied conditions under which groups and communities are likely to under- or overharvest the common resource in both the laboratory and field. Research programs have concentrated on a number of motivational, strategic, and structural factors that might be conducive to commons management.
In game theory, which constructs mathematical models for individuals´ behavior in strategic situations, the corresponding "game", developed by the ecologist Garrett Hardin, is known as the Commonize Costs — Privatize Profits Game (CC–PP game).
Motivation to conserve a common resource is also promoted by people’s group ties. When people identify with their group they are more likely to exercise personal restraint as well as compensate for greedy harvest decisions of ingroup members more so than outgroup members. Similarly, in the field strongly knit communities are usually better at managing resource shortages than communities with weak social ties. It might be that group identity promotes a long-term perspective on resource management which makes it easier for people to sacrifice their immediate interest on behalf of their local community. It could also be that group identification increases the social interdependencies between community members so that they care more for the social rewards and punishments of their community. This needs further investigation.
The state of the common resource can also shape motivations. One motivational factor is people’s attributions of the state of the commons. Research has manipulated the reasons people were given for resource overuse. When greedy people were seen as causing the depletion participants were more greedy than when there was deemed to be a natural cause (like a sudden drought). Resource uncertainty further contributes to over-harvesting. In commons dilemmas uncertainty about the pool size tends to increase individual harvesting and expectations about how much other people harvest. When there is uncertainty people overestimate the size of the resource and perceive greater variability in how much other people take. Similarly uncertainty about the replenishment rate of the pool also increases harvesting. The most likely explanation is that people have an optimistic bias.
Another structural solution is the privatization of the commons and this has been very effective in experimental and field research. It is difficult to imagine how common moveable resources such as fish, water, and clean air can be privatized. Privatization also raises concerns about social justice as not everyone may be able to get an equal share. Finally, privatization might erode people’s personal and social motivations to cooperate in preserving a resource.
The provision of rewards and punishments might also be effective in preserving common resources. Selective punishments for overuse can be effective in promoting domestic water and energy conservation, for instance, through installing water and electricity meters in houses. Selective rewards also work provided that they are open to everyone. An experimental carpool lane in the Netherlands failed because car commuters did not feel they were able to organize a carpool. Hence they showed reactance against this pro-environment intervention. There has been much field research on commons dilemmas which has combined solutions obtained in experimental research. The seminal work of Elinor Ostrom and her colleagues is worth mentioning. They have looked at how real-world communities manage communal resources such as fisheries, land irrigation systems, and farm lands and came up with a number of factors conducive to successful resource management. One factor is the resource itself. Resources with definable boundaries (land) can be preserved much easier. A second factor is resource dependence. There must be a perceptible threat of resource depletion and it must be difficult to find substitutes. The third is the presence of a community. Small and stable populations with a thick social network and social norms promoting conservation do better. A final condition is that there are appropriate community-based rules and procedures in place with built-in incentives for responsible use and punishments for overuse.