Coercion is the threat or use of force to alter behavior. Hardin believes that, given the failure of all other attempts at limiting population, the only way to achieve population control is through legislation enforcing limits on family size. Hardin’s idea of coercion isn’t arbitrary or malicious; he sees it as the proper function of civil societies when dealing with problems that can’t be solved at the individual level: “The only kind of coercion I recommend is mutual coercion, mutually agreed upon by the majority of the people affected” (Section 9, Paragraph 3). 

A commons is a place or resource open to public use, usually without charge, such as a pasture, park, forest, river, etc. A desirable commons may attract more people until it’s overused and begins to fail. An unregulated commons, the type discussed in Hardin’s essay, has no rules for users to follow: “Freedom in a commons brings ruin to all” (Section 3, Paragraph 6). Examples in 1968, the year the article was published, included the atmosphere, oceans, rivers and lakes, wilderness areas, and other resources large enough for any one user to exploit without much effect but which, when exploited by millions, would suffer degradation.