On Liberty

John Stuart Mill published On Liberty in 1859, the year after his wife Harriet Taylor died. He had been working on it with her for years, and the book is dedicated to her memory. It is one of the most carefully argued works of political philosophy in the English language, and its central argument — the harm principle — has structured debates about freedom of expression and individual autonomy ever since.

The harm principle, stated simply, is this: the only legitimate reason for society to interfere with an individual’s conduct is to prevent harm to others. Not harm to the individual themselves. Not offence to prevailing morals. Not the disapproval of the majority. Only harm to others. Mill derives this principle not from natural rights — he was impatient with natural rights arguments — but from utility: the greatest happiness of the greatest number is best served, in the long run, by allowing individuals maximum freedom.

The argument for free expression in Chapter Two is the most important section of the book and one of the most important arguments in the liberal tradition. Mill offers four reasons why suppressing opinion is always wrong, regardless of whether the opinion is true or false:

First, the suppressed opinion might be true. We are not infallible. History is full of cases where majority opinion was wrong and minority opinion was right.

Second, even if the suppressed opinion is partly false, it probably contains some element of truth that the dominant opinion lacks. Progress comes from the collision of partial truths.

Third, even if the dominant opinion is wholly true, without challenge it will become a dead dogma rather than a living truth — held by habit rather than understanding.

Fourth, the meaning of the doctrine itself will be in danger of being lost if it is not tested by vigorous argument.

These arguments were controversial in 1859 and they remain controversial now. Mill’s defenders argue that the internet has proved him right: the free exchange of ideas, even bad ideas, ultimately benefits society. His critics argue that the internet has proved him wrong: some speech causes direct harm, and the marketplace of ideas does not reliably produce truth.

Reading On Liberty now is to engage with an argument that is still alive.