Chapter 1
Introductory
Mill states the question and the principle. The fight is no longer against kings — it is against the tyranny of prevailing opinion. The harm principle is introduced, and the sphere of personal liberty is marked out.
On Liberty — chapter by chapter
All five chapters — from the harm principle to its application in the cases.
On Liberty is short and exactly organised. Chapter 1 states the question and the rule. Chapter 2 defends free expression at length, with four distinct arguments. Chapter 3 turns from speech to life: why individuality matters and how custom hollows it out. Chapter 4 draws the line between what society may judge and what it may not coerce. Chapter 5 tests the doctrine in the cases — trade, schooling, marriage, vice — and closes with a warning about the administrative state. Five chapters, one sustained argument.
Part 1 · The principle
The harm principle, the tyranny of the majority, and the sphere of liberty.
Part 2 · The arguments
Free expression defended on four grounds; individuality as a positive good.
Chapter 2
Of the Liberty of Thought and Discussion
The longest and most-quoted chapter. Mill defends free expression on four grounds — truth, partial truth, the decay of received opinion, and the fading of living doctrine — and argues that suppression is always an error, however well-intentioned.
Chapter 3
Of Individuality, as One of the Elements of Well-being
Having defended liberty of thought, Mill defends liberty of life. A person who lets custom choose for him exercises no faculty higher than imitation. Individuality is the soil in which character grows; society needs room for the different, or the average is flattened by its own weight.
Part 3 · The limits and the cases
What society may and may not do; the doctrine tested in practice.
Chapter 4
Of the Limits to the Authority of Society over the Individual
Mill draws the line between what society may judge and what it may not coerce. Disapproval, advice, and avoidance are legitimate; legal penalty is not, unless definite harm to others is at stake. The objection that no act is purely self-regarding is answered precisely.
Chapter 5
Applications
The harm principle is tested in the cases. Trade, education, marriage, drink, vice — each receives a careful, partial answer. The book closes with a warning: a state that does everything for its citizens eventually cannot be corrected by them.