In the final chapter of On Liberty, Mills tries to clarify his general argument. He writes that his essay can be broken down into two basic principles. First, people are not accountable to society for actions that only concern themselves. The only means society has to express disapproval of such actions is through "advice, instruction, persuasion, and avoidance by other people if thought necessary by them for their own good." Secondly, the individual is accountable for actions that hurt others, and society can punish a person socially or legally as is deemed necessary for such actions. Mill observes, though, that sometimes when an action causes harm to others, such as when a person succeeds in a competitive job market, the general social good is positive, and there is no right to punish people for the harm caused. Similarly, free trade is allowed because of its socially beneficial effects.
In the rest of the chapter Mill looks at particular examples, and explains how his argument should be properly applied to each one.
Mill first looks at how liberty relates to society's right to guard against crimes and accidents. Mill says that the police must be careful not to restrict things that might only potentially be done for evil, and must respect people's right to potentially harm themselves. For example, a person should be warned about the danger of crossing an unstable bridge, but should not be forcibly prevented from crossing if he understands the risks. In the case of a poison that could be potentially used for a crime, there should be regulations such as taking down the name and address of the purchaser, but the poison should not be banned. Mill also observes that the right to prevent crimes makes it legitimate to limit conduct in the interest of prevention. For example, a person who becomes violent when drunk could be compelled not to drink. He also mentions that public violations of "decency" are an affront to others, and can therefore be restricted.
Mill then turns to the issue of whether people should be free to "counsel or instigate" others to act in a particular way. He says that they should, because of the importance of exchanging opinions. A more complicated situation is when someone profits from acting against the public good, such as in owning a gambling house. On the one hand, society does not have the right to keep a person from trying to persuade people to do something bad. On the other hand, Mill does not think it unreasonable for society to say that people should not be allowed to benefit from prompting others to make bad decisions. Rather, a bad decision should reflect only the individual's will. Mill acknowledges that persuading people to act badly for profit is an evil, and accepts that society could impose restrictions on such people. Another issue is whether the state should discourage vices through powers like taxation. Mill rejects this, saying that it represents a punishment. Since it is not acceptable to ban vices it is not acceptable to punish people for them either.
Mill addresses the question of whether people should be held to agreements that cause themselves harm, such as selling oneself into slavery. Mill says that a person should not be held to this agreement, because he is thereby permanently giving up his freedom, and thereby undermining the very significance of freedom. However, Mill does recognize that since agreements often create expectations and obligations, these factors must be taken into account in determining whether it is acceptable to nullify a particular agreement.
Mill also complains that certain actions affecting other people are currently seen as being protected by a right to liberty. In particular, Mill writes about the case of "family relations." In these cases actions can harm other people, and it is in the State's authority to make sure such harms do not occur. For example, the State should be allowed to legislate compulsory education for children (while allowing for different modes of education), regardless of the desires of the parent. To leave children uneducated is a crime against society and the child, and the state should be able to test that children have general knowledge of facts. Mill also contends that the State should be allowed to restrict marriage to those people capable of supporting a family, given the dangers of over-population and the duty to give children a chance at a normal existence.