“The only part of the conduct of any one, for which he is amenable to society, is that which concerns others.”John Stuart Mill · Despre libertate · 1859 · capitolul IV
Society may only intervene in actions that affect others.
Mill establishes the core principle of liberty: each person is sovereign over their own life as long as they do not harm others. The mechanism is a clear boundary between the private and public spheres. For example, smoking in your own home is a personal choice, but smoking in an enclosed space with others becomes a social matter because it affects their health.
Why it matters This principle is the foundation of modern debates on drug legalization, free speech, and the limits of state intervention.