John Stuart Mill’s enduring arguments for free speech

Last updated June 14, 2024

If you could trace every pro-free speech argument you’ve ever heard back to John Stuart Mill, it’d be no surprise.

The British philosopher’s 1859 essay “On Liberty” remains one of the most concise and comprehensive defenses of individual freedom ever written. In its second chapter, “Of the Liberty of Thought and Discussion,” Mill laid out extensive appeals for free speech, free inquiry, and open discourse that are still quoted by lawyers, teachers, journalists, and free speech advocacy organizations like FIRE to this day.

But what did Mill actually say about free speech? Why has his commentary stood the test of time? In this explainer, I’ll break down the most potent and powerful free speech arguments in “On Liberty,” why they matter, and how they still apply nearly two centuries later.

Mill’s three-pronged defense of free speech, free inquiry, and open debate

Many proponents of individual liberty tend to focus on governmental authority as the prime danger to their personal freedoms. But the threat to free expression that most worried Mill didn’t come from the government. Rather, it came from the conformity imposed on individuals by society.

This is why Mill began the chapter by noting the potential dangers of what he calls the “tyranny of the majority,” arguing for “protection…against the tyranny of the prevailing opinion and feeling; against the tendency of society to impose…its own ideas and practices as rules of conduct on those who dissent from them.”

It’s easy to understand the drawbacks of a king, dictator, or aristocracy’s opinions trumping all others. One person or group can be fallible, destructive, or malicious in asserting their authority, causing widespread suffering for the sake of a powerful few.

But majority opinion in democratic societies can be just as fallible, just as powerful, and just as dangerous — especially when backed by the government:

[Government silencing of speech] 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 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.

But why should the single minority opinion still be heard? 

This is where Mill laid out his three-pronged argument for why no opinions — regardless of how poorly-subscribed or incorrect they are — should be silenced. FIRE president Greg Lukianoff calls it Mill’s Trident, and describes it as follows:

“In any argument there are only three possibilities. You are either wholly wrong, partially wrong, or wholly correct — and in each case free speech is critical to improving or protecting those positions.”

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Prong One: The silenced opinion might be correct

Mill’s first point is the most obvious: Humans are prone to error and overconfidence, and our opinions — even if held by the vast majority — may be wrong. Silencing dissent not only neglects this fact but also actively prevents our errors from being corrected.

“All silencing of discussion is an assumption of infallibility,” Mill wrote. “To refuse a hearing to an opinion because they are sure it is false is to assume that their certainty is the same thing as absolute certainty.”

History is rife with examples of absolute certainty getting in the way of progress. The idea that the Earth was round, for instance, challenged prevailing orthodoxies and was actively suppressed by the powers that be. Hindsight allows us to clearly see this mistake, but what’s so different about our current moment? 

The fatal tendency of mankind to leave off thinking about a thing when it is no longer doubtful is the cause of half their errors.

“Ages are no more infallible than individuals,” Mill wrote. “It is as certain that many opinions, now general, will be rejected by future ages, as it is that many, once general, are rejected by the present.”

However confident we may be, we should avoid the certainty that prevents us from hearing opinions we dislike. As Mill pointed out: “The fatal tendency of mankind to leave off thinking about a thing when it is no longer doubtful is the cause of half their errors.”

But what about things we know are false? Why should we tolerate arguments in favor of flat Earth, for example, now that we know beyond all reasonable doubt that they’re provably wrong?

To this, Mill argued that airing even erroneous opinions still has value — both for those who hold them and for those who do not.

Prong Two: Even falsehoods improve our understanding of the truth

“The peculiar evil of silencing the expression of an opinion is that it is robbing the human race,” Mill wrote. “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.”

Mill argued that the foundation of knowledge goes much further than simply holding factually correct views. It is just as important, if not more so, to understand why those views are correct and why the opposition is wrong. The surest way to gain that understanding is through constant conflict with robust dissent — even if that dissent is incorrect.

Truth gains more even by the errors of one who, with due study and preparation, thinks for himself, than by the true opinions of those who only hold them because they do not suffer themselves to think.

“So essential is this discipline to a real understanding of moral and human subjects,” Mill wrote, “that if opponents of all important truths do not exist, it is indispensable to imagine them.”

To Mill, the mere restatement of facts — even incontrovertible ones — without understanding why they are facts, is “dead dogma,” and its adherents are akin to religious zealots. This leads to one of Mill’s most famous and often-quoted arguments in favor of open discourse:

He who knows only one side of the case, knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side; if he does not so much as know what they are, he has no ground for preferring either opinion.

Above all this, Mill saved his harshest criticism not for those who keep themselves from hearing dissent, but those who deprive others of hearing it.

“The usefulness of an opinion is itself [a] matter of opinion: as disputable, as open to discussion and requiring discussion as much, as the opinion itself,” he wrote. “It is not the feeling sure of a doctrine (be it what it may) which I call an assumption of infallibility. It is the undertaking to decide that question for others, without allowing them to hear what can be said on the contrary side.”

And for those worried that constant engagement with falsehoods will eventually erode the truth, Mill noted that “Truth gains more even by the errors of one who, with due study and preparation, thinks for himself, than by the true opinions of those who only hold them because they do not suffer themselves to think.”

These points highlight Mill as one of the earliest evangelists for a culture of free speech in human history. England did not have anything like the First Amendment to the Constitution (and still doesn’t), and nowhere in “On Liberty” did Mill suggest that it should ratify such a law.

Mill was thinking beyond government authority and focusing on promoting free speech in and among individual citizens. Eighty-five years before Judge Learned Hand would remark that “Liberty lies in the hearts of men and women,” and that “when it dies there, no constitution, no law, no court can even do much to help it,” the Englishman John Stuart Mill was extolling the importance of free speech as a cultural value.

Only through diversity of opinion is there, in the existing state of human intellect, a chance of fair play to all sides of the truth

So far, we’ve covered the first two prongs in Mill’s Trident: If we’re wrong, hearing dissent helps us correct our errors. If we’re right, dissent helps us strengthen our arguments and understanding.

But how often is someone actually at either of those rhetorical extremes?

Not often at all. And that’s where the final prong in Mill’s Trident comes in.

Prong Three: Most arguments are neither true nor false, but a mixture of both

“One-sidedness has always been the rule, and many-sidedness the exception,” Mill wrote. “Hence, even in revolutions of opinion, one part of the truth usually sets while another rises.”

Our flawed perceptions being what they are, it will be a rare moment when any one person or any one group possesses the full and complete picture of reality. This is why opposition must not only be valued, but actively sought out and encouraged.

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“Very few have minds sufficiently capacious and impartial to make the adjustment with an approach to correctness,” Mill wrote, “and it has to be made by the rough process of a struggle between combatants fighting under hostile banners.”

Mill believed that one of the most important functions of a culture of free inquiry is keeping one another honest. It’s easy to succumb to bias, motivated reasoning, and delusion when we are alone and unchallenged. “Only through diversity of opinion is there, in the existing state of human intellect, a chance of fair play to all sides of the truth,” he wrote.

This is perhaps the most important of Mill’s three main appeals for free speech and against silencing dissent: As flawed individuals, we can never know the full truth. But by uniting and colliding our perspectives with those of others, we can get ever closer to it — and ensure that our minds don’t stagnate even after we’ve found it.

Why John Stuart Mill’s arguments for free speech endure

Despite being a fierce and principled proponent of free expression (and freedom in general), Mill held no illusions that free speech would eliminate all dogmatism, ignorance, or division.

“I acknowledge that the tendency of all opinions to become sectarian is not cured by the freest discussion, but is often heightened and exacerbated thereby,” he wrote. “The truth which ought to have been, but was not seen, being rejected all the more violently because proclaimed by persons regarded as opponents.”

However, Mill also knew that the game was much bigger:

It is not on the impassioned partisan, it is on the calmer and more disinterested bystander, that this collision of opinions works its salutary effect. Not the violent conflict between parts of the truth, but the quiet suppression of half of it, is the formidable evil; there is always hope when people are forced to listen to both sides; it is when they attend to only one that errors harden into prejudices, and truth itself ceases to have the effect of truth, by being exaggerated into falsehood.

In the age of social media, livestreamed debates, and long-form podcasts where guests and hosts duke it out on issues of the day — often in the most tribal ways possible — it is a benefit to the audiences and the public that all perspectives are aired and critiqued.

Mill believed that partisanship and tribalism weren’t nearly as bad as echo chambers, because the latter keep people from even seeing that there is another side to an argument. It’s in that circumstance that dissent or difference begins to be seen as not just wrong, but evil. When disfavored views are suppressed on that basis, all the benefits of engagement become unattainable.

For these reasons, Mill’s careful and considered defense of “absolute freedom of opinion and sentiment on all subjects, practical or speculative, scientific, moral, or theological,” remains relevant even two centuries after the publication of “On Liberty.” Mill was able to see clearly what so many advocates for censorship still fail to recognize or concede: Without a constant search for truth, the ability to recognize it when we find it, and the capacity to intelligently discern it from falsehood through discussion and debate, how can we ever know we’re on the right track? How can we ensure we stay on track?

Mill understood that free speech, free inquiry, and open debate are the keys to human progress. They aren’t just vital to human well-being, but foundational. As he wrote in conclusion to his second chapter of “On Liberty,” these are the human freedoms “on which all their other well-being depends.”