Mill warned about the complacency of this view. He said that the elected government distils the views of the majority, and this majority might end up wanting to oppress the minority. This “tyranny of the majority” meant that there was a risk that interference by even elected governments would have harmful effects. At least as serious as political tyranny was the risk of the social tyranny of public opinion, which tends to lead to conformity of belief and action. These forms of tyranny were all the more serious, argued Mill, because people’s opinions were often unthinking, rooted in little more than self-interest and personal preference. Ultimately, the received wisdom is then nothing more than the interests of a society’s most dominant groups.

  Britain at the time was still going through the transition towards a modern democracy, and Mill said that people did not yet appreciate the dangers. The prevailing mistrust of government was a relic from the era in which the state was viewed as a threat to individuals, and the potential for tyranny by a democratic majority was not yet widely understood. This confusion meant that the government’s actions were both unnecessarily called for and unjustifiably condemned. Also, the tyranny of public opinion was on the rise and Mill feared a general tendency for society to increase its control over the individual.

Freedom of action—such as the right of assembly at this gay pride parade in Paris—was central to Mill’s idea of individual liberty, alongside freedom of thought and freedom of opinion.

A moral dam was needed to stop this trend, so Mill attempted to set out a clear principle to define the right balance between individual autonomy and government interference. He argued that society could only justifiably interfere with individuals’ liberties in order to prevent harm to others. Concern for the individual’s own good might justify an attempt to persuade him to take a different course of action, but not to compel him to do so: “Over himself, over his own body and mind, the individual is sovereign,” Mill said. This principle of individual liberty applied to thought, to the expression of opinions, and to actions.

Mill argued that if this principle is undermined, the whole of society suffers. Without freedom of thought, for example, human knowledge and innovation would be restricted. To demonstrate this, Mill put forward an account of how humans arrive at truth. Because human minds are fallible, the truth or falsity of an idea only becomes known by testing it in the bubbling cauldron of opposing ideas. By stifling ideas, society might lose a true idea. It might also suppress a false idea that would have been useful to test and potentially reveal the truth of another idea. Mill rejected the argument that some ideas are more socially useful than others irrespective of their truth. He believed that this argument assumes infallibility in deciding which beliefs are useful. Although heretics were no longer burned at the stake, Mill believed that the social intolerance of unorthodox opinions threatened to dull minds and cramp the development of society.

Even when society’s received wisdoms were true, Mill argued that it was important to maintain a profusion of ideas—for a true idea to keep its vitality and power, it needs to be constantly challenged and probed. This was particularly the case with ideas about society and politics, which can never attain the certainty of mathematical truths. Testing ideas is best done by hearing the views of those who hold conflicting opinions. Where there are no dissenters, their views must be imagined. Without this discussion and argument, people will not appreciate the basis of even true ideas, which then become dead dogmas, parroted without any real understanding. Correct principles of behavior and morality, when they have been converted into barren slogans, can no longer motivate authentic action.

Mill used his principle of liberty to defend the individual’s freedom to act. However, he acknowledged that freedom of action would necessarily be more limited than freedom of thought, because an action is more capable of hurting others than a thought. Like freedom of ideas, individuality—the freedom to live an unorthodox life—promotes social innovation: “the worth of different modes of life should be proved practically,” he said. Although people might usefully draw on traditions as a guide to their own lives, they should do so creatively in ways that are especially relevant to their particular circumstances and preferences. Mill believed that when people automatically follow customs—in a similar way to the impact of unthinkingly held opinions—ways of living become sterile, and the individual’s moral faculties are weakened.

In Mill’s bubbling cauldron of ideas, each idea must constantly be tested against other ideas. The cauldron acts like a still. False, or broken, ideas evaporate away as they are rejected, while true ideas are left in the mix and grow stronger.

As with the free expression of ideas, those who act in new ways provide a benefit to society as a whole, even to conventional people. Nonconformists discover new ways of doing things, some of which can then be adopted by others. But social innovators need to be free to experiment for these benefits to be realized.

  Given the power of the majority view, free spirits and eccentrics help to inspire people toward new ways of doing things. When Mill wrote On Liberty, the Industrial Revolution had made Britain the most economically advanced country in the world. Mill believed that this success had come from the relative plurality of thought and freedom of action that existed in Europe. He contrasted the dynamism of Europe with the stagnation of China, which he believed had declined because customs and traditions had hardened and suppressed individuality. In Britain, economic development had brought mass education, faster communications, and greater opportunities for previously excluded social classes. But this progress also brought a greater homogeneity of tastes and, with it, a decline in individuality. He believed that if this trend continued, England would suffer the same fate as China. Mill thought that English society had already become too conformist and unappreciative of the value of individuality and originality. People acted in accordance with social rank, not their consciences. This is why he believed that a lack of eccentricity was such a danger.

Mill’s criterion of harm was a useful and easily stated principle to define the appropriate boundary between state and individual, expressed at a time when the relationship between the government and the people was going through rapid change.

  Policies on smoking during the 20th century illustrate how the principle can be used as a way of thinking about government restrictions on individual behavior. Although it had long been understood that tobacco did people harm, society had never prevented individuals from smoking. Instead, health information was supplied to persuade people to stop smoking and, by the late 20th century, smoking was declining in the US and many European countries.

This was in line with Mill’s principle of liberty: people could freely smoke even though it harmed them, because it did not harm others. Then new medical information came to light showing that passive smoking was harmful. This meant that smoking in public places now violated the harm principle. The principle was reapplied, and smoking bans in public places were initiated to reflect this new knowledge. With its rapid decline in popularity, smoking has in a sense become a habit of eccentrics, but despite the increasing evidence about the health dangers, few would advocate an outright ban.

Demonstrators protest at a neo-Nazi rally. Mill held that individual liberty—such as the neo-Nazis’ right to gather—could be opposed if it led to more unhappiness than happiness.

The harm principle may not always deliver the results imagined by liberals, however. For example, if people found homosexuality immoral and repugnant, they might argue that the mere knowledge that homosexuality was being practiced would harm them. They might argue that the state should intervene to uphold sexual morals. This raises the issue of the underlying ethical basis for Mill’s defense of the individual. On Liberty was written in the context of the philosophical system of utilitarianism, which Mill espoused. Mill was a follower of the English philosopher Jeremy Bentham, who argued that the morality of actions should be judged according to the extent to which they contribute to the sum total of human happiness. For instance, instead of judging lying as wrong in itself, one would need to condemn it because its various consequences—when reckoned together—cause more unhappiness than happiness. Mill refined and developed Bentham’s theory, for example by making a distinction between “higher” and “lower” pleasures, meaning that it would be better to be born an unhappy Socrates than a happy pig, because only a Socrates has the possibility of experiencing higher pleasures.

  One might perceive a conflict between utilitarianism and the approach taken in On Liberty, because the defense of individual liberty sounds like a separate principle, which might conflict with the happiness principle that takes precedence in a utilitarian approach. If homosexuality made the majority unhappy, for instance, utilitarianism would recommend that it should be banned, which would be a clear infringement of individual liberty. Despite this apparent conflict, Mill maintains that utility is still the ultimate, overarching principle in his system.

  Mill is not making an absolutist argument for individual autonomy. One way of viewing his argument is as concrete application of the happiness principle in the area of state versus individual action: Mill argues that liberty leads to social innovation and the growth of knowledge, which then contribute to happiness. This leaves open the possibility that Mill may have been too optimistic in thinking that the happiness principle always points towards liberty. He may even have been too optimistic with respect to the expression of opinions, not just to behavioral norms. For example, some might argue that the banning of the expression of certain opinions—the declaration of support for Adolf Hitler in today’s Germany, for example—reduces unhappiness and is therefore justifiable on utilitarian grounds.

A religious preacher addresses onlookers at Speaker’s Corner in Hyde Park, London. Mill argued against censorship and for freedom of speech, whatever the opinion being expressed.

Another criticism that could be leveled at Mill’s arguments concerns the way in which he believes that truth bubbles up from the cauldron of opposing ideas. He believes that this cauldron bubbles most vigorously when society completely avoids any interference with individual thought or action. This is a notion of liberty that the British political theorist and philosopher Isaiah Berlin later called “negative liberty”, which he defines as the absence of constraints on actions.

Leftist critics consider negative liberty alone to be insufficient. They point out that oppressed groups—such as the poorest in society, or women without rights—might have no way of expressing their unorthodox views: they are marginalized, which means that they have little access to the media and institutions in which opinions are expressed and publicized. For this reason, those on the left often argue that negative liberties are meaningless without “positive liberties”, which actively help to give marginalized people the power to express their opinions and influence policy. If he had witnessed the achievements of feminism over the 20th century, Mill might well have argued that women did manage to obtain political equality through the vigorous expression of their views. However, leftists would counter once more that formal political rights mean little without positive liberties, such as the provision of equal pay and guaranteed employment rights.

Mill’s political philosophies—utilitarianism and his defense of liberty—have had a profound influence on the development of liberal democracies throughout the world. His is perhaps the most famous and frequently cited argument for a pragmatic form of liberalism, which is tied to a principle of collective well-being rather than arguing for abstract, inalienable rights.

  In modern liberal democracies, particularly in the US and the UK, many debates—such as those on sexual morality, smoking, and even the role of free markets in the economy—have been structured around the considerations that Mill put forward nearly two centuries ago. But even in these countries, many social constraints on individual actions are justified by more than just the minimal criterion of negative liberty. Bans on recreational drugs, for example, depend on a paternalistic principle, and even in free market countries, the government regulates commerce and attempts to make economic outcomes more equal. These are all actions that may be considered to go beyond Mill’s condition for intervention, but as the debates about the appropriate scope of social control continue unabated, those arguing for more liberal stances often invoke the arguments made by Mill.