『On Liberty』要約

John Stuart Mill’s *On Liberty*, published in 1858, is one of the foundational texts of modern political liberalism. Mill’s central concern is the proper limit of society’s power over the individual, and he answers it with what became known as the harm principle: the only justification for coercing someone against their will is to prevent harm to others. His own good, whether physical or moral, is not sufficient warrant. The essay unfolds in five chapters, moving from liberty of thought and discussion, to individuality as one of the elements of well-being, to the limits of society’s authority over the individual, and finally to applications of his doctrine. Mill’s argument for free expression rests on the claim that silenced opinion may be true, that even false opinion sharpens truth through contest, and that received truths held as dead dogma lose their living force. In the individuality chapter, he draws on Wilhelm von Humboldt’s idea of “the absolute and essential importance of human development in its richest diversity,” defending eccentricity and experiments in living against the tyranny of custom and the “despotism of society.” He distinguishes self-regarding acts from other-regarding acts, though critics note the boundary is often hard to draw. Mill also warns of the tyranny of the majority operating through public opinion rather than law. The work remains a touchstone in debates over free speech, paternalism, and the scope of state authority.