The 1859 book On Liberty by British philosopher John Stuart Mill presents one of the most influential arguments ever formulated in favor of free speech and individual freedom over censorship and paternalism. The importance of On Liberty resides in a series of powerful arguments defending the free flow of ideas in a marketplace of ideas, and in the belief that individuals can best make their lifestyle choices, free from government intervention. On Liberty was thus an inspiration for future First Amendment theory.

According to Mill, protection against the tyranny of the government magistrate is not enough to ensure individual freedom. Protection is also needed against the tyranny of prevailing opinion, which seeks to suppress dissent and enforce conformity. The central concern of On Liberty is to find a way to draw the line between “individual independence and social control”—that is, under what circumstances is society warranted in interfering in a person’s life? To this question Mill responds: “The sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection.That the only purpose for which power can be rightfully exercised over any member of a civilized community,against his will, is to prevent harm to others.His own good, either physical or moral, is not a sufficient warrant.”

Chapters 3, 4, and 5 of On Liberty are devoted to an extended series of arguments against paternalism. In these arguments, Mill asserts that individuals are their own best judges of their tastes and preferences, and therefore they should be permitted to make their own choices if they are to grow and flourish as individuals. Mill also contends that were society to interfere, it would often do so wrongly. Overall, the thrust of these parts is to effect a wall between one’s private and public life, with society having no right to interfere in the private life.

Chapter 2 of On Liberty is a defense of freedom of thought and expression and an argument against censorship. Mill offers several arguments in favor of free expression. First, because no one knows the truth, censoring an idea may be censoring the truth. Second, free competition of ideas is the best way to find truth. Third, because no one idea is the sum of truth, even those ideas containing only a portion of the truth will help society acquire knowledge. This argument implies that even false ideas are valuable, because they both test the truth and prevent it from slipping into dogma, and because they too may contain a germ of truth worth preserving. In summary, the robust exchange of ideas will help preserve individuality, restrain the tyranny of social opinion, and guide the pursuit of truth.

On Liberty has played a role many constitutional law theories. It has been important in the defense of a right to privacy against individual freedom, in areas of sexual autonomy, and in the choice of reading material and religion. But the real power of the book has been in conceptualizing the First Amendment as a marketplace of ideas in which the truth of ideas is determined not by bowing to government fiat or censorship, but by letting dissenters burn flags or crosses, protest, or publish ideas that challenge the prevailing orthodoxy in society. Perhaps the best statement of the embodiment of On Liberty in the Constitution was in West Virginia State Board of Education v. Barnette (1943). The Supreme Court, in striking down a compulsory flag salute law, declared: “If there is any fixed star in our constitutional constellation, it is that no official, high or petty, can prescribe what shall be orthodox in politics, nationalism, religion, or other matters of opinion.”

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