John Stuart Mill's classic has at its heart a brave (some might say Quixotic) attempt to define both the constraints on individual freedom, and the degree of coercion governments may legitimately use to limit that freedom. His solution is a "very simple principle" - that one may coerce only to defend oneself or others from harm. This deceptively straightforward axiom has deep social consequences - it would, for example, ban all government intervention to make populations behave 'better'. The resulting ramifications have been argued over by social scientists for more than 150 years, and never more so than in modern times.