On Liberty

On Liberty is about one question: when may society, through the law or through public opinion, interfere with what an individual does? Mill’s answer fits in a sentence. “The only purpose for which power can be rightfully exercised over any member of a civilised community, against his will, is to prevent harm to others.” His own good is not enough.

That is the harm principle, and most of the book tests it. The second chapter, on freedom of thought and discussion, is the best known. If all mankind minus one were of one opinion, Mill writes, mankind would be no more justified in silencing that one person than he would be in silencing mankind. A suppressed opinion may be true. If it is false, the truth still needs it, because a belief nobody challenges hardens into dead dogma. Then he moves to individuality, to the limits of society’s authority, and to applications, where the principle meets drink, trade, contracts and education, and gets more complicated.

Mill worried less about kings than about neighbours. The tyranny he had in mind was social: the steady pressure of custom and opinion, which needs no police and reaches further than they do. That is why the book still reads as current. Most arguments about speech, on a campus or online, are at some point arguments with chapter two.

He published it in 1859, the year after his wife, Harriet Taylor Mill, died, and dedicated it to her as the inspirer and in part the author of all that was best in his writing. Mill had been raised as an experiment in education, with Greek at three, and he writes like it: clear, patient and slightly relentless.

This edition is 180 pages. It is short enough to read in a weekend and argue about for considerably longer.