One hundred years ago today, the Supreme Court weighed in for one of the first times in history on the meaning of the First Amendment, deciding that it did not actually guarantee Americans the unlimited right to say anything they’d like, at any time, in any setting. Through that ruling, the high court forever changed the country’s legal understanding of the First Amendment.

In Schenck v. United States, the justices held that all language — speeches, phone calls, letters, pamphlets, news articles, books — must be evaluated in context. Words that could be spoken or written in peacetime, for example, might amount to criminal offenses in wartime. In short, the First Amendment, which prohibited Congress from “abridging the freedom of speech, or of the press,” had limitations, ones that still are with us today.

The Schenck decision was shaped by American experiences during World War I. In 1917, Germany stepped up its attacks on U.S. shipping, leading Congress to declare war on Germany and send U.S. troops to Europe. But President Woodrow Wilson could not take public support for granted — after all, many Americans, including the country’s sizable German-American population, had reasons to oppose a war against Germany.

So Wilson launched a wide-scale program of propaganda and domestic censorship. Congress went even further with the Espionage and Sedition Acts. These laws banned traditional forms of spying for America’s enemies in wartime, then went much further, making it a crime to even express certain ideas. Prosecutors quickly began filing criminal charges against thousands of Americans for criticizing the war. Defendants pushed back, arguing that the First Amendment protected them from such prosecution.

Even after the war ended in 1918, the legal conflicts persisted, eventually making their way to the Supreme Court.

The first of those cases involved Charles T. Schenck of Philadelphia, a socialist charged with trying to thwart the wartime military draft. His weapon: a piece of paper, more specifically, a two-sided pamphlet similar to the kind written by Thomas Paine and others fighting for American liberty more than a century earlier. Schenck’s pamphlet argued that the draft was not only unconstitutional but the government’s way of coercing the working class to do the bidding of Wall Street. Schenck was charged and convicted under the Espionage Act on the grounds that the pamphlet would obstruct the operations of the draft.

The Supreme Court ultimately upheld the ruling. In the unanimous opinion, Justice Oliver Wendell Holmes wrote that Schenck’s attempt to induce his readers to resist the military draft was intolerable, at least in wartime. “The character of every act depends upon the circumstances in which it is done,” Holmes wrote, then followed with this famous phrase: “The most stringent protection of free speech would not protect a man in falsely shouting fire in a theatre and causing a panic.”

According to Holmes, Schenck was guilty of inciting his readers to action — an action which the government had legitimate reason to suppress or punish. Words, Holmes declared, have consequences. “The question in every case is whether the words used are used in such circumstances and are of such a nature as to create a clear and present danger,” he continued, firing off another of the most familiar phrases in American law. If words create a “clear and present danger” by bringing about something criminal, then Congress may be able to ban such speech despite the First Amendment. It all depends on the circumstances.

This ruling, which made pamphleteering against the draft a crime, paved the way for Supreme Court rulings that have since limited press freedom. Before Schenck, many Americans believed the First Amendment was absolute. The Sedition Act of 1798, for example, outraged opponents who warned that under such a law, newspapers would be “deterred from printing anything.” Even Abraham Lincoln shut down only a few opposition newspapers during the Civil War, and then only as a last resort.

That changed with Schenck. Holmes’s ruling meant that once the United States launched a war, there was no room left under the Constitution for debate — not about the war’s ultimate wisdom, the rightness of its aims or the effectiveness of the tactics.

Holmes recognized this danger in a ruling on another case involving a political pamphlet, decided several months after Schenck. The case began when a group of young Russian immigrants printed pamphlets opposing the war and tossed them from a building in Lower Manhattan. Military intelligence agents quickly traced the pamphlets to their authors, rounded up half a dozen Russian immigrant anarchists and socialists (including a man named Jacob Abrams) and charged them with violating the Espionage Act. The defendants were quickly convicted and sentenced to up to 20 years in prison.

In late 1919, Abrams v. United States. went to the Supreme Court on appeal. But this time the Court split. Citing the reasoning laid out by Holmes eight months earlier in Schenck, the majority upheld the convictions. Holmes, however, was in the minority this time.

Why? After a summer of soul searching about press freedom, Holmes underwent something of a conversion. In October, he wrote in a letter to a friend that, although he still had doubts about the wisdom of an absolute freedom of speech, he considered the principle so important that, he wrote, “I hope I would die for it.”

He made this clear in his dissent in Abrams. “The best test of truth is the power of the thought to get itself accepted in the competition of the market,” Holmes wrote, “and that truth is the only ground upon which their wishes safely can be carried out. That at any rate is the theory of our Constitution.”

With this view in mind, Holmes said there was no question that the constitutional rights of Abrams and his co-defendants had been violated. He had come around to the now-dominant view in democratic thought that the people are best served when truth and error are free to do battle in a wide-open “marketplace of ideas” in which the government plays no role. For Abrams and his fellow pamphleteers, however, it was no solace. They stayed in prison.

The troubling legacy of 1919 is that, despite popular belief to the contrary, the First Amendment does not guarantee an absolute right to freedom of speech or the press. In a number of rulings involving anti-Semitism, communism, the Ku Klux Klan, national security and terrorism, the high court has built an edifice of law upon the limits initially laid out in Schenck.

The Sedition Act was ultimately repealed by an act of Congress after the war. The Espionage Act, however, is still very much with us. It provides the statutory basis for the unceasing efforts of presidents to punish “leakers” and the journalists who report on those leaks, a continuing threat to press freedom.

Americans should be concerned about any limits on their freedoms. Judging from the wartime reporting in recent decades about the Pentagon Papers case, the My Lai Massacre and the Abu Ghraib torture scandal, the record suggests that Americans need a free and robust news media every bit as much in wartime as in peacetime.