Until World War II it was a uniquely American practice to give courts, especially the Supreme Court, a significant role in the structure of governance. No other democratic society had a constitution enforced by judges. In Britain and its empire, the doctrine of parliamentary supremacy prevailed; whatever a parliament did—however discriminatory, however unjust—was law. But the tyrannies of the twentieth century brought a change.

Aharon Barak, then the president of the Israeli Supreme Court, explained the change in a 1998 lecture. In the past, he said, people thought that respect for basic values “could be guaranteed by relying on the self-restraint of the majority.” But after the Nazis, the lesson was that there must be “formal limits on the power of the majority. The concept that ‘It is not done’ needs to receive the formal expression, ‘It is forbidden.’ ”

And so, country after country adopted constitutional democracy, giving the last word to judges on basic issues. That was the pattern in a state with as profound a republican system as France, and then in a reconstructed Germany. It was followed in the great former British territories, notably India and South Africa. And the countries of Europe adopted a European Convention on Human Rights, enforced by a Court of Human Rights. In time, even Britain agreed that its own courts should be bound by the European Convention.

As the history of the First Amendment shows, putting a guarantee into a charter is no assurance that it will be enforced. After all, it took more than a century for the courts to begin protecting dissenting speakers and publishers from official repression in the United States. Or to put it another way, it took time for judges to build on the fundamental promise of those fourteen words in the First Amendment: that this would be a country of free speech and freedom of the press. Time and imagination and courage. Timid, unimaginative judges could not have made America as extraordinarily free as it is.

Freedom to speak and write as you wish is the inescapable necessity of democracy. The judges of the European Court of Human Rights understood that when, in 1986, they considered the right to criticize political leaders. They did not consider the issue in a vacuum; they built on American experience and decisions.

An Austrian journalist, Peter Michael Lingens, had written articles charging a politician with the “basest opportunism.” The politician sued for libel, and the Austrian courts awarded him damages. Lingens went to the European Court of Human Rights, which found that the libel judgment against him violated the Convention on Human Rights—its clause guaranteeing freedom of expression. That freedom, the court said, “constitutes one of the essential foundations of a democratic society. . . . It is applicable not only to ‘information’ or ‘ideas’ that are favorably received or regarded as inoffensive . . . but also to those that offend, shock or disturb. Such are the demands of that pluralism, tolerance and broadmindedness without which there is no ‘democratic society.’” In other words, as Justice Oliver Wendell Holmes Jr. of the United States Supreme Court said, “freedom for the thought that we hate.”

When a constitutional provision has no discernible history, as is true of the First Amendment—no meaningful discussion by its authors of what they meant—how do judges begin to build on its words to decide concrete cases? That is a subject of endless debate. But one thing is sure. Judges, however bold, are part of their society and are influenced by its attitudes. To give a stark example: The Nazi experience made more Americans, and judges, understand the devastating character of religious and racial discrimination.

Justice Ruth Bader Ginsburg of the Supreme Court, speaking at the University of Cape Town, South Africa, in 2006, said: “What caused the Court’s understanding to dawn and grow? Judges do read newspapers and are affected, not by the weather of the day, as distinguished constitutional law professor Paul Freund once said, but by the climate of the era.”

Justice Ginsburg was talking about gender discrimination. But her point applies to the drama of the First Amendment’s expanding interpretation since early in the twentieth century. Great judges like Holmes saw, before most judges and most Americans, that freedom of thought was an essential element in the success of our diverse society. But judicial commitment to openness of expression grew as citizens’ did; each informed the other. And it is worth remembering that the 1798 statute criminalizing criticism of the president, which was enforced by judges, was rejected by American voters in the election of 1800 as incompatible with the First Amendment and with American ideals.

The meaning of the First Amendment has been, and will be, shaped by each American generation: by judges, political leaders, citizens. There will always be authorities who try to make their own lives more comfortable by suppressing critical comment. There will always be school principals like the one in Wilton, Connecticut, who in 2007 canceled a student play about the war in Iraq because it might disturb some families. But I am convinced that the fundamental American commitment to free speech, disturbing speech, is no longer in doubt.