John Stuart Mill's On Liberty turns 150 this year. Published in 1859, this slender manifesto for human liberty went on to become a classic of modern philosophy and political science. It remains a beautiful articulation of the core principles of human liberty and a just society.

Anyone familiar with the book recognizes the importance of the opening chapter and Mill's "one very simple principle" for "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. He cannot rightfully be compelled to do or forbear because it will be better for him to do so, because it will make him happier, because, in the opinions of others, to do so would be wise, or even right. These are good reasons for remonstrating with him, or reasoning with him, or persuading him, or entreating him, but not for compelling him, or visiting him with any evil in case he do otherwise. To justify that, the conduct from which it is desired to deter him, must be calculated to produce evil to some one else. 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.

Mill went on to outline "the appropriate region of human liberty," and divided it into:

1. "liberty of conscience, in the most comprehensive sense; liberty of thought and feeling; absolute freedom of opinion and sentiment on all subjects, practical or speculative, scientific, moral, or theological. The liberty of expressing and publishing opinions may seem to fall under a different principle, since it belongs to that part of the conduct of an individual which concerns other people; but, being almost of as much importance as the liberty of thought itself, and resting in great part on the same reasons, is practically inseparable from it."


2. "liberty of tastes and pursuits; of framing the plan of our life to suit our own character; of doing as we like, subject to such consequences as may follow: without impediment from our fellow-creatures, so long as what we do does not harm them, even though they should think our conduct foolish, perverse, or wrong"


3. "freedom to unite, for any purpose not involving harm to others"

Bringing it altogether, he argued:

The only freedom which deserves the name, is that of pursuing our own good in our own way, so long as we do not attempt to deprive others of theirs, or impede their efforts to obtain it. Each is the proper guardian of his own health, whether bodily, or mental and spiritual. Mankind are greater gainers by suffering each other to live as seems good to themselves, than by compelling each to live as seems good to the rest.

To this day, I do not believe there has been a more eloquent or concise summation of the central principles of libertarianism than those passages from Chapter 1 of the book. But what many fail to remember or appreciate is the equally powerful second chapter of Mill's treatise, "On the Liberty of Thought and Discussion." It was a bold defense of freedom of speech and expression that was many decades ahead of its time. And it still has lessons and warnings worth heeding in our modern Information Age.

Mill opened that chapter by noting that:

The time, it is to be hoped, is gone by, when any defence would be necessary of the "liberty of the press" as one of the securities against corrupt or tyrannical government. No argument, we may suppose, can now be needed, against permitting a legislature or an executive, not identified in interest with the people, to prescribe opinions to them, and determine what doctrines or what arguments they shall be allowed to hear.

Alas, Mill knew that we weren't quite there yet in 1859. Efforts to suppress speech and expression were alive and well. And so he marshaled all his intellectual forces to construct a powerful critique of censorship in all its forms:

The power itself is illegitimate. The best government has no more title to it than the worst. It is as noxious, or more noxious, when exerted in accordance with public opinion, than when in opposition to it. If all mankind minus one, were of one opinion, and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person, than he, if he had the power, would be justified in silencing mankind. Were an opinion a personal possession of no value except to the owner; if to be obstructed in the enjoyment of it were simply a private injury, it would make some difference whether the injury was inflicted only on a few persons or on many. But the peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error. ... We can never be sure that the opinion we are endeavouring to stifle is a false opinion; and if we were sure, stifling it would be an evil still.

Mill went on to show how, at root, censorship is based on arrogance and elitism:

Those who desire to suppress [an opinion], of course deny its truth; but they are not infallible. They have no authority to decide the question for all mankind, and exclude every other person from the means of judging. To refuse a hearing to an opinion, because they are sure that it is false, is to assume that their certainty is the same thing as absolute certainty. All silencing of discussion is an assumption of infallibility. Its condemnation may be allowed to rest on this common argument, not the worse for being common.

More profoundly, Mill taught us that the right to freedom of thought and expression was a core right upon which almost all our other rights depended:

Complete liberty of contradicting and disproving our opinion, is the very condition which justifies us in assuming its truth for purposes of action; and on no other terms can a being with human faculties have any rational assurance of being right.

In other words, if you care about any other rights and wish to exercise them to their fullest, you must first have the right to express opinions and, importantly, have them subjected to the opinions of others. This is how truth is discovered.

[Man] is capable of rectifying his mistakes by discussion and experience. Not by experience alone. There must be discussion, to show how experience is to be interpreted. Wrong opinions and practices gradually yield to fact and argument: but facts and arguments, to produce any effect on the mind, must be brought before it. Very few facts are able to tell their own story, without comments to bring out their meaning.

And Mill taught us that it is essential we be vigilant in defending our rights of speech and expression because, sadly, "the dictum that truth always triumphs over persecution, is one of those pleasant falsehoods which men repeat after one another till they pass into commonplaces, but which all experience refutes. History teems with instances of truth put down by persecution," he correctly noted.

Mill's words are every bit as relevant in 2009 as they were 1859. While we enjoy significant speech and press freedoms here in the United States today, censorial threats persist. Just a few years ago, the House of Representatives passed the Deleting Online Predators Act (DOPA), which proposed a ban on all social networking sites in public schools and libraries. DOPA passed the House of Representatives shortly thereafter by a remarkably lopsided 410-15 vote, but luckily failed to get through the Senate. However, Congress did pass several other online censorship measures in the 1990s, including the Communications Decency Act of 1996 and the Child Online Protection Act (COPA) of 1998, which luckily were both struck down by the courts.

Of course, we have it pretty good here in the States thanks the existence of the First Amendment to our Constitution. Most speech-restricting enactments get struck down today because they cannot withstand strict scrutiny under the First Amendment. But think about all those less fortunate in other countries who struggle on a regular basis to express themselves and learn the truth about the world and culture around them without interference from above.

Anyway, go give On Liberty another read if you haven't done so in some time. It's a timeless statement of the principles that should guide a just society. I'll close with this apt warning from Mill about how history will remember those who fail to appreciate the importance of openness to new ideas:

And so far from the assumption being less objectionable or less dangerous because the opinion is called immoral or impious, this is the case of all others in which it is most fatal. These are exactly the occasions on which the men of one generation commit those dreadful mistakes, which excite the astonishment and horror of posterity.