On Liberty is one of Mill’s most famous works and remains the one most read today. In this book, Mill expounds his concept of individual freedom within the context of his ideas on history and the state. On Liberty depends on the idea that society progresses from lower to higher stages and that this progress culminates in the emergence of a system of representative democracy. It is within the context of this form of government that Mill envisions the growth and development of liberty.

Chapter I defines civil liberty as the limit that must be set on society’s power over each individual. Mill undertakes a historical review of the concept of liberty, beginning with ancient Greece and Rome and proceeding to England. In the past, liberty meant primarily protection from tyranny. Over time, the meaning of liberty changed along with the role of rulers, who came to be seen as servants of the people rather than masters. This evolution brought about a new problem: the tyranny of the majority, in which a democratic majority forces its will on the minority. This state of affairs can exercise a tyrannical power even outside the political realm, when forces such as public opinion stifle individuality and rebellion. Here, society itself becomes the tyrant by seeking to inflict its will and values on others. Next, Mill observes that liberty can be divided into three types, each of which must be recognized and respected by any free society. First, there is the liberty of thought and opinion. The second type is the liberty of tastes and pursuits, or the freedom to plan our own lives. Third, there is the liberty to join other like-minded individuals for a common purpose that does not hurt anyone. Each of these freedoms negates society’s propensity to compel compliance.

Chapter II examines the question of whether one or more persons should be able to curtail another person’s freedom to express a divergent point of view. Mill argues that any such activity is illegitimate, no matter how beyond the pale that individual’s viewpoint may be. We must not silence any opinion, because such censorship is simply morally wrong. Mill points out that a viewpoint’s popularity does not necessarily make it correct—this fact is why we must allow freedom of opinion. Dissent is vital because it helps to preserve truth, since truth can easily become hidden in sources of prejudice and dead dogma. Mill defines dissent as the freedom of the individual to hold and articulate unpopular views.

Chapter III discusses whether people who hold unpopular views should be allowed to act on them without being made social outcasts or facing a legal penalty. Actions cannot be as free as ideas or viewpoints, and the law must limit all actions whose implementation would harm others or be an outright nuisance. He states that human beings are fallible, and therefore they need to experiment with different ways of living. However, individual liberty must always be expressed in order to achieve social and personal progress.

Chapter IV examines whether there are instances when society can legitimately limit individual liberty. Mill rejects the concept of the social contract, in which people agree to be a part of society and recognize that society can offer certain forms of protection while asking for certain forms of obligations. However, he does suggest that because society offers protection, people are obliged to behave in a certain way, and each member of society must defend and protect society and all its members from harm. In brief, society must be given power to curtail behavior that harms others, but no more.

Chapter V summarizes and elucidates Mill’s twofold argument. First, individuals are not accountable to society for behavior and actions that affect only them. Second, a person is answerable for any type of behavior or action that harms others, and in such cases it is the responsibility of society to punish and curtail such behavior and action. However, Mill does note that there are some types of actions that certainly harm others but bring a larger benefit to society, as when one person succeeds in business more than his rival. In the rest of the chapter, Mill examines particular examples of his doctrine.