Constitution, that right is very much in the news. Campus speech codes, disinvited commencement

speakers, jailed performance artists, exiled leakers, a blogger condemned to a thousand

lashes by one of our closest allies, and the massacre of French cartoonists have forced

the democratic world to examine the roots of its commitment to free speech.

Is free speech merely a symbolic talisman, like a national flag or motto? Is it just

one of many values that we trade off against each other? Was Pope Francis right when he

said that �you cannot make fun of the faith of others�? May universities muzzle some

students to protect the sensibilities of others? Did the Charlie Hebdo cartoonists �cross

a line that separates free speech from toxic talk,� as the dean of a school of journalism

recently opined? Or is free speech fundamental � a right which, if not absolute, should

be abrogated only in carefully circumscribed cases?

The answer is that free speech is indeed fundamental. It�s important to remind ourselves why,

and to have the reasons at our fingertips when that right is called into question.

The first reason is that the very thing we�re doing when we ask whether free speech is fundamental

� exchanging and evaluating ideas � presupposes that we have the right to exchange and evaluate

ideas. In talking about free speech (or anything else) we�re talking. We�re not settling

our disagreement by arm-wrestling or a beauty contest or a pistol duel. Unless you�re

willing to discredit yourself by declaring, in the words of Nat Hentoff, �free speech

for me but not for thee,� then as soon as you show up to a debate to argue against free

speech, you�ve lost it.

Those who are unimpressed by this logical argument can turn to one based on human experience.

One can imagine a world in which oracles, soothsayers, prophets, popes, visionaries,

imams, or gurus have been vouchsafed with the truth which only they possess and which

the rest of us would be foolish, indeed, criminal, to question. History tells us that this is

not the world we live in. Self-proclaimed truthers have repeatedly been shown to be

mistaken � often comically so � by history, science, and common sense.

Perhaps the greatest discovery in human history � one that is prior to every other discovery

� is that our traditional sources of belief are in fact generators of error and should

be dismissed as grounds for knowledge. These include faith, revelation, dogma, authority,

charisma, augury, prophesy, intuition, clairvoyance, conventional wisdom, and subjective certainty.

How, then, can we know? Other than by proving mathematical theorems, which are not about

the material world, the answer is the process that the philosopher Karl Popper called conjecture

and refutation. We come up with ideas about the nature of reality, and test them against

that reality, allowing the world to falsify the mistaken ones. The �conjecture� part

of this formula, of course, depends upon the exercise of free speech. We offer these conjectures

without any prior assurance they are correct. It is only by bruiting ideas and seeing which

ones withstand attempts to refute them that we acquire knowledge.

Once this realization sank in during the Scientific Revolution and the Enlightenment, the traditional

understanding of the world was upended. Everyone knows that the discovery that the Earth revolves

around the sun rather than vice-versa had to overcome fierce resistance from ecclesiastical

authority. But the Copernican revolution was just the first event in a cataclysm that would

make our current understanding of the world unrecognizable to our ancestors. Everything

we know about the world � the age of our civilization, species, planet, and universe;

the stuff we�re made of; the laws that govern matter and energy; the workings of the body

and brain � came as insults to the sacred dogma of the day. We now know that the beloved

convictions of every time and culture may be decisively falsified, doubtless including

some we hold today.

A third reason that free speech is foundational to human flourishing is that it is essential

to democracy and a bulwark against tyranny. How did the monstrous regimes of the 20th

century gain and hold power? The answer is that groups of armed fanatics silenced their

critics and adversaries. (The 1933 election that gave the Nazis a plurality was preceded

by years of intimidation, murder, and violent mayhem.) And once in power, the totalitarians

criminalized any criticism of the regime. This is also true of the less genocidal but

still brutal regimes of today, such as those in China, Russia, African strongman states,

and much of the Islamic world.

Why do dictators brook no dissent? One can imagine autocrats who feathered their nests

and jailed or killed only those who directly attempted to usurp their privileges, while

allowing their powerless subjects to complain all they want. There�s a good reason dictatorships

don�t work that way. The immiserated subjects of a tyrannical regime are not deluded that

they are happy, and if tens of millions of disaffected citizens act together, no regime

has the brute force to resist them. The reason that citizens don�t resist their overlords

en masse is that they lack common knowledge � the awareness that everyone shares their

knowledge and knows they share it. People will expose themselves to the risk of reprisal

by a despotic regime only if they know that others are exposing themselves to that risk

at the same time.

Common knowledge is created by public information, such as a broadcasted statement. The story

of �The Emperor�s New Clothes�� illustrates the logic. When the little boy shouted that

the emperor was naked, he was not telling them anything they didn�t already know,

anything they couldn�t see with their own eyes. But he was changing their knowledge

nonetheless, because now everyone knew that everyone else knew that the emperor was naked.

And that common knowledge emboldened them to challenge the emperor�s authority with

their laughter.

The story reminds us why humor is no laughing matter � why satire and ridicule, even when

puerile and tasteless, are terrifying to autocrats and protected by democracies. Satire can stealthily

challenge assumptions that are second nature to an audience by forcing them to see that

those assumptions lead to consequences that everyone recognizes are absurd.

That�s why humor so often serves as an accelerant to social progress. Eighteenth-century wiseguys

like Voltaire, Swift, and Johnson ridiculed the wars, oppressions, and cruel practices

of their day. In the 1960s, comedians and artists portrayed racists as thick-witted

Neanderthals and Vietnam hawks and nuclear cold warriors as amoral psychopaths. The Soviet

Union and its satellites had a rich underground current of satire, as in the common definition

of the two Cold War ideologies: �Capitalism is the exploitation of man by man; Communism

is the exact opposite.�

We use barbed speech to undermine not just political dictators but the petty oppressors

of everyday life: the tyrannical boss, the sanctimonious preacher, the blowhard at the

bar, the neighborhood enforcer of stifling norms.

It�s true that free speech has limits. We carve out exceptions for fraud, libel, extortion,

divulging military secrets, and incitement to imminent lawless action. But these exceptions

must be strictly delineated and individually justified; they are not an excuse to treat

speech as one fungible good among many. Despots in so-called �democratic republics� routinely

jail their opponents on charges of treason, libel, and inciting lawlessness. Britain�s

lax libel laws have been used to silence critics of political figures, business oligarchs,

Holocaust deniers, and medical quacks. Even Oliver Wendell Holmes�s famous exception

to free speech � falsely shouting �Fire!� in a crowded theater � is easily abused,

not least by Holmes himself. He coined the meme in a 1919 Supreme Court case that upheld

the conviction of a man who distributed leaflets encouraging men to resist the draft during

World War I, a clear expression of opinion in a democracy.

And if you object to these arguments � if you want to expose a flaw in my logic or a

lapse in my accuracy � it�s the right of free speech that allows you to do so.