For Mill, the term liberty encompasses both civil and social liberty, which he defines as "the nature and limits of the power of which can be legitimately exercised by society over the individual." Mill argues that society can only exert authority over behavior that harms other people, anything else is an abrogation of individual freedom.

Tyranny of the Majority

This is the concept that in a democratic state a majority of people can impose its will on a minority. Mill believes this behavior is "tyrannical" when it violates a claim that the minority has as a member of society.

Public Opinion

In Mill’s essay, the power of public opinion can become a pernicious tool in stifling individuality and dissent. Indeed, he states, public opinion can be more powerful in this regard than laws. He writes that there must also be protection for people against the prevailing public opinions, and the tendency of society to impose its values on others.

Dead Dogma

A term that Mill cites in one of his arguments in favor of opinion in Chapter 2. He uses dead dogma to describe what can happen to popular ideas that are no longer debated since they are so widely accepted. If truth is simply held as a prejudice, then people will not fully understand it, and will not understand how to refute objections to it. Dissent, even if it is false, keeps alive the truth against which it dissents.

Social Contract

This reflects the idea that society is something that people either explicitly or implicitly agreed to be part of. Social contract theory was first formulated by Jean-Jacques Rousseau in The Social Contract that defines rights as those things that people would have agreed to have protected by society, and duties as those things people would have agreed to take on as obligations, had they been present at the formation of the state.


The quality of being capable of making mistakes and being wrong.


The quality of being incapable of making a mistake or being wrong.

Harm Principle

A central concept to arguments made by Mills in On Liberty. The harm principle is the notion that actions should only be punishable when they lead to the harm f others.


Mill’s theory of utilitarianism as explicted in his 1861 essay Utilitarianism is based on the principle that “actions are right in proportion as they tend to promote happiness, wrong as they tend to produce the reverse of happiness.” By  explicitly calling his justification of liberty utilitarian, Mill says outright that his defense of liberty will not be based on natural rights or metaphysical claims, but rather on what is best for mankind. On Liberty can be understood as an attempt to broaden the meaning of utility and show that utilitarianism can provide a strong protection of rights.

Moral Policing

A force cited by Mill in his arguments against the majority interfering in the ideas and practices of individuals that they find to be immoral. Moral policing occurs when a majority seeks to prohibit individuals from practices of ideas that the majority believes to be incorrect—such as outlawing the consumption of alcohol or banning recreation on the Sabbath.

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