Applications

Mill takes the doctrine into practice. Trade is a social act — it affects others — and therefore falls under the rule permitting social intervention; but most actual restraints on trade are bad policy rather than violations of liberty as such. Education is treated more sharply: the state may require that children be educated, because failure to educate a child is a wrong against the child. But it must not monopolise the schools. Uniform state education produces uniform minds, and a government with the power to form every citizen's thinking holds a power no government should want.

Mill works through the regulation of vice — drink, gambling, prostitution — with careful, partial answers and without the easy moralism of his age. Where a practice harms only the person who chooses it, the harm principle gives society no warrant to prohibit it; where it harms assignable others, the calculus changes. He refuses both the moralist who wants law to enforce virtue and the libertarian who denies every civic claim. Each case gets its own answer, and the answers are not comfortable.

The book closes with a warning that is its deepest argument. A state that absorbs into itself every able person and every important function — that does everything for its citizens and decides everything in their place — may run things efficiently for a while. But it dries up the springs of independent judgment and independent life on which the state's own capacity to change and correct itself depends. Liberty is not only good for the person who exercises it. It is the condition of a society that remains capable of governing itself well.