When and how should the government (or society, more generally) intervene in the activities of individuals, and when should individuals go about their business free of government constraint?

The pioneering text addressing this issue is On Liberty, written by John Stuart Mill and published in 1859. Mill gave a simple answer to the question of the propriety of social compulsion, one that has become known as the “harm principle”:

Social coercion exercised over you for your own well-being, in the absence of “harm to others,” is a violation of your individual liberty. Of course, Mill quickly offers the necessary child-excluding qualification, “that this doctrine is meant to apply only to human beings in the maturity of their faculties.”

Mill noted that, in the absence of a general principle, society was apt to intervene in individual decision making in circumstances where the intervention would likely be unhelpful and to fail to intervene when intervention was merited. The harm principle is useful in part because its application in most cases accords well with the intuitions developed in liberal democracies. For instance, under the harm principle, the government has no business regulating what color I paint my living room, but society does have an interest in ensuring that my children are protected against abuse and have access to education.