John Stuart Mill dominated liberal thought during the nineteenth century with insights offered into the harm principle, free will, the despotism of custom, experiments in living, utilitarianism, the marketplace of ideas and electoral reform. Taken together, no theorist has contributed more to liberalism than John Stuart Mill.

Given its broader legacy towards political theory and the legal system, it seems fitting to begin with the harm principle. John Stuart Mill makes a crucial distinction between self-regarding and other-regarding actions. Ultimately, we should be free to pursue those actions that in no way constrain the liberty of others. We should therefore be able to engage in self-regarding actions. The state (on behalf of society) is only justifying in limiting our actions when those actions impinge upon the freedom of others. Mill’s conception of free will flows seamlessly from his previous work on the harm principle. John Stuart Mill begins with the proposition that we are sovereign entities capable of exercising free will. As such, we should accept responsibility for charting our own path in life. In contrast, “he who lets the world … choose his plan of life for him has no need of any other faculty than the apelike one of imitation.”

Later in life Mill modified his limited view of the role of government. He accepted that some degree of state intervention was justified to prevent the poor from enduring injustice. He believed that income should be taxed at a single rate (the so-called 'flat tax'), but he was in favour of inheritance tax, because the transmission of wealth across the generations gave some individuals an advantage over others. In this sense he represents a bridge between classical and modern liberalism.

Mill also upheld the idea of tolerance and the right of people to express a minority view. He believed that just because an opinion was widely held across society, that did not

necessarily make it correct. For example, he spent a night in jail for trying to advise the poor on contraception, which in Victorian England was seen as a taboo subject. His private life was unconventional, especially by the standards of his time; he lived for 21 years with the love of his life, Harriet Taylor, and her first husband, marrying her after the latter died. Mill believed in the complete equality of men and women, which was unusual even among radical liberals in his time, and during his brief period as a Liberal MP (1865-68) he unsuccessfully championed votes for women.

Mill was concerned that universal suffrage would lead to the tyranny of the majority and in On Liberty he explored how individual freedom could be protected . He argued that the franchise should be based on an educational qualifi cation, but also supported the vote for women . As well as being a philosopher, Mill was a liberal MP and civil servant . In his later years he changed his view about the limited role of the state and argued that liberalism should tackle social problems rather than blaming the working classes for disadvantages for which they were not responsible 

With regards to the despotism of custom, Mill warns us against the mediocrity of public opinion. He believes there is a tendency to tell everyone to act in the same manner. Sadly, the despotism of custom seeks to crush self-expression and is therefore contrary to the right and proper goal of a liberal society. We need to facilitate “experiments in living” in order that freedom is experienced to the very full. A liberal society is one that tolerates the full diversity of lifestyles.

“The despotism of custom is everywhere the standing hindrance to human advancement, being in unceasing antagonism to that disposition to aim at something better than customary, which is called, according to circumstances, the spirit of liberty, or that of progress or improvement.”

― John Stuart Mill, On Liberty 

In order to guard against the despotism of custom, we must avoid forcing our opinions on others unless we are certain of their truth. In order to ascertain the truth, assumptions must be subject to the marketplace of ideas. In doing so, the truth will emerge from discussion and experience. For instance, it is essential that we play Devil’s advocate in order to establish that which holds true. In addition, Mill states that a ‘fact’ must face the rigours of open debate. This is arguably most relevant in the context of religion. Belief in a deity often comes with the proviso that followers seek to convert others. However, throughout history the desire to convert has come at a price of appalling bloodshed and repression. Many people have subconsciously followed Mill’s advice and not sought to convert others towards their faith.

Mill also points out that majority opinion can be wrong as the majority holds no true authority and no absolute certainty. To support this argument, Mill cites popular opinion of the past which has since been rejected by contemporary society. What was therefore received wisdom in the past may no longer hold that status. Similarly, that which is accepted as right in the present day may well be rejected at some point in the future as sexist or racist (i.e. Mill himself assumed that the British Empire was part of the white man’s burden of civilising lesser people). Ultimately, Mill believed that we must also be free to question beliefs within society. The majority can easily misjudge potentially good ideas for society. They may adopt a reactionary mindset grounded in tradition. In doing so, they prevent the emergence of measures that would improve society.

'There is one characteristic of the present direction of public opinion, peculiarly calculated to make it intolerant of any marked demonstration of individuality. The general average of mankind are not only moderate in intellect, but also moderate in inclinations: they have no tastes or wishes strong enough to incline them to do anything unusual, and they consequently do not understand those who have, and class all such with the wild and intemperate whom they are accustomed to look down upon.'    John Stuart Mill, On Liberty 

With regards to utilitarianism, John Stuart Mill believed that “actions are right in proportion as they tend to promote happiness, wrong as they tend to produce the reverse of happiness.” However, he departs from Bentham in his view of what constitutes happiness – claiming that higher pleasures are superior to the simple pursuit of pleasure. This is expressed quite clearly in his famous assertion that “it is better to be Socrates dissatisfied than a fool satisfied.” Mill therefore adopts a more qualitative aspect to his search for the greatest happiness for the greatest number than Jeremy Bentham. Indeed, it is worth noting that Bentham believed that in regard to quantifying pleasure “pushpin was as good as poetry.”

Throughout his life, John Stuart Mill was a passionate advocate of electoral reform. Most notably, Mill is one of the very few male theorists who could credibly be labelled as a feminist. He advocated female emancipation long before the issue was on the political agenda. Indeed, it is not unfair to call him a pioneer of the first-wave of feminist thought. Mill also favoured proportional representation long before it was a mainstream cause.