The liberal project was (and is) to a large extent about controlling the exercise of power. If its holders are unaccountable, power will be abused. It is a certainty. Mill noted that the powers of government had historically come to be checked in two ways. First, there was the notion of inviolable rights which the sovereign could not encroach upon. Second, there was the doctrine that some of the more important decisions of state required the consent of the nation or of a parliament. Once elective government had developed, however, the notion of checks on the sovereign power had come to be seen as obsolete. But this still left "the tyranny of the majority" (a phrase which Mill did not invent). This tyranny was expressed not only through laws, but also through public opinion and social censure. It is often forgotten that Mill's horizons extended beyond politics and civil liberties as we would understand them today, and that he was as concerned with emancipation from "the despotism of custom" as he was from freedom from state authority. He wrote that in England in particular, "the yoke of opinion is perhaps heavier, [and] that of law is lighter, than in most other countries of Europe".
Mill sought to identify a means of determining when the government, or society at large, was justified in interfering with an individual's conduct:
There is... no recognised principle by which the propriety or impropriety of government interference is customarily tested. People decide according to their personal preferences. Some, whenever they see any good to be done, or evil to be remedied, would willingly instigate the government to undertake the business; while others prefer to bear almost any amount of social evil, rather than add one to the departments of human interests amenable to governmental control....
The object of this Essay is to assert one very simple principle, as entitled to govern absolutely the dealings of society with the individual in the way of compulsion and control, whether the means used be physical force in the form of legal penalties, or the moral coercion of public opinion. That principle is, that the sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection. That the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others. His own good, either physical or moral, is not a sufficient warrant.... The only part of the conduct of any one, for which he is amenable to society, is that which concerns others. In the part which merely concerns himself, his independence is, of right, absolute. Over himself, over his own body and mind, the individual is sovereign.He affirms elsewhere that "neither one person, nor any number of persons, is warranted in saying to another human creature of ripe years, that he shall not do with his life for his own benefit what he chooses to do with it". The "ripe years" qualifier is significant: Mill applied his doctrine only to mature adults, not to minors or to barbarian societies. Even where other people were harmed, individuals' conduct was not necessarily to be penalised: this was the case in such circumstances as where a person had passed an exam or got a job in front of another.
The most important section of the book is where Mill discusses freedom of opinion and argues that one can never be entirely certain that one's convictions on any particular issue are correct. It would be no exaggeration to say that this epistemological humility is the foundation and basis of political and religious liberalism. Affecting to be a believing Christian (which he was not), Mill writes:
The man who left on the memory of those who witnessed his life and conversation, such an impression of his moral grandeur, that eighteen subsequent centuries have done homage to him as the Almighty in person, was ignominiously put to death, as what? As a blasphemer. Men did not merely mistake their benefactor; they mistook him for the exact contrary of what he was, and treated him as that prodigy of impiety, which they themselves are now held to be, for their treatment of him.... These were, to all appearance, not bad men — not worse than men most commonly are, but rather the contrary; men who possessed in a full, or somewhat more than a full measure, the religious, moral, and patriotic feelings of their time and people: the very kind of men who, in all times, our own included, have every chance of passing through life blameless and respected. The high-priest who rent his garments when the words were pronounced, which, according to all the ideas of his country, constituted the blackest guilt, was in all probability quite as sincere in his horror and indignation, as the generality of respectable and pious men now are in the religious and moral sentiments they profess; and most of those who now shudder at his conduct, if they had lived in his time, and been born Jews, would have acted precisely as he did. Orthodox Christians who are tempted to think that those who stoned to death the first martyrs must have been worse men than they themselves are, ought to remember that one of those persecutors was Saint Paul.As for the idea that truth will always triumph over persecution, this was "one of those pleasant falsehoods which men repeat after one another till they pass into commonplaces". Even where the cause of truth is not extirpated by persecution, it may be put back by hundreds of years. Mill goes on to argue, a little more counter-intuitively, that it would be wrong in any event to suppress an undoubtedly false opinion. If the truth is not exposed to counter-argument, he says, "it will be held as a dead dogma, not a living truth". In fact, says Mill, opposing parties usually each possess a portion of the truth, and it is a healthy thing to let them contend amongst themselves. Mill gives the example of rival conservative and liberal political parties, whose coexistence ensures the equipoise of the state.
Mill acknowledges that a right to freedom of opinion does not necessarily translate into a corresponding right to act on one's opinions. It was one thing to publish an article in a newspaper arguing that corn-dealers are starvers of the poor or that private property is theft. It was another to stir up a mob assembled in front of a corn-dealer's house. He believed, however, in the freedom to express oneself in one's personal conduct - in individualism, in other words, or "individuality":
It is not by wearing down into uniformity all that is individual in themselves, but by cultivating it and calling it forth, within the limits imposed by the rights and interests of others, that human beings become a noble and beautiful object of contemplation; and as the works partake the character of those who do them, by the same process human life also becomes rich, diversified, and animating, furnishing more abundant aliment to high thoughts and elevating feelings, and strengthening the tie which binds every individual to the race, by making the race infinitely better worth belonging to.... Even despotism does not produce its worst effects, so long as individuality exists under it; and whatever crushes individuality is despotism, by whatever name it may be called, and whether it professes to be enforcing the will of God or the injunctions of men.In a world which tended towards mediocrity, individualists performed an educational function. After all (this is still Mill talking) we don't want to be like the Chinese, do we?
It was fine for citizens to be concerned about each other's wellbeing, and even to disapprove when their fellow citizens acted in ways that were harmful to themselves. However, actual "reprobation" and punishment should be restricted to cases where individuals were engaging in acts that were harmful to others. A drunkard should be left unmolested unless it was apparent that he became violent when drunk, at which point the law could intervene. Mill was aware that such distinctions might prove difficult to draw in practice - after all, is it not true that no man is an island? Are not many modes of behaviour injurious to society in an indirect or general sense? The answer was that, where no specific harm to another could be identified, "the inconvenience is one which society can afford to bear, for the sake of the greater good of human freedom". After all, society has the whole of a person's childhood to inculcate her with right principles without extending its authority into her adulthood as well.
Mill is not without his blind spots. A modern liberal would be likely to see social justice, as well as a lack of coercion from society or the state, as an integral part of enabling individuals to enjoy the highest degree of freedom. This inevitably requires some level of government action. Mill, however, objected to governmental intervention to benefit society, mainly because he feared the consequences of a strong state. He didn't like the idea of a governmental bureaucracy (he refers in this connection to Tsarist Russia - goodness knows what he would have made of the USSR), and he explicitly rejected the notion that sections of the economy should be nationalised. However, he was not what a modern commentator might regard as an anti-government nut. He believed, for example, that the state could legitimately prevent couples from marrying if they didn't have means to support a family, and that it could intervene to ensure that children received a proper education.
Such was Mill's view of human liberty; and in large part it can fairly be said that his ideas have stood the test of time.