The age of terror: Is the American standard of free speech outdated?

The intensifying focus on terrorism — and on the Islamic State in Iraq and the Levant, in particular — poses a fresh challenge to the greatest American contribution to the theory and practice of free speech: the "clear and present danger" test. In both the U.S. and Europe, it's worth asking whether that test may be ripe for reconsideration.

As developed by Supreme Court Justices Oliver Wendell Holmes and Louis Brandeis in the first decades of the 20th century, the clear and present test ensures strong protection for almost all speech, forbidding the government from regulating speech unless the danger is both likely ("clear") and imminent ("present"). If a person were to say that "the U.S. government should be overthrown" or "the more acts of terrorism, the better" or that "all Muslims should join ISIL," she couldn't be punished unless those statements were likely to produce imminent lawless action.

As it is usually understood, that test protects a lot of dangerous speech, including many forms of recruitment and propaganda for terrorist purposes. Holmes himself issued a stern warning against "attempts to check the expression of opinions that we loathe and believe to be fraught with death."

It is important to appreciate that the "clear and present danger" test was accepted relatively recently. In their time, Holmes and Brandeis were dissenters; the Supreme Court didn't fully adopt their view until 1969. Both during and after World War I, the free-speech principle was widely understood to allow the government to punish speech whenever it had a "bad tendency," meaning a tendency to produce harm.

As the court ruled in 1925, there would be no protection of speech whose "natural tendency and probable effect was to bring about the substantive evil which the legislative body might prevent." Under this test, of course, terrorist recruitment activity would not be protected.

As late as 1951, the Supreme Court allowed regulation of speech even when the danger was neither clear nor present. In Dennis vs. United States, the court upheld a conviction of people trying to organize the Communist Party to overthrow the U.S. government. The justices refused to understand the "clear and present danger" test to "mean that, before the Government may act, it must wait until the putsch is about to be executed, the plans have been laid and the signal is awaited."

In words that could easily be repeated today, the court found it sufficient that the revolutionaries wanted to "strike when they thought the time was ripe." When the safety of the community was at grave risk, because of "an apparatus designed and dedicated to the overthrow of the Government, in the context of world crisis after crisis," the government could act to stop horrific harm, even if it was neither likely nor imminent.

Hand preferred his approach to the "clear and present danger" test, which he thought squishy. By contrast, he defended his exemption of incitement as a "qualitative formula, hard, conventional, difficult to evade."

For decades, the court has shown zero interest in Hand's formula. Most people have regarded the Dennis decision as an epic blunder, a product of the Red Scare, not to be taken seriously in a free society. Brandeis offered the best reason: "If there be time to expose through discussion the falsehood and fallacies, to avert the evil by the processes of education, the remedy to be applied is more speech, not enforced silence." In his view, "only an emergency can justify repression."

It's an excellent thought, and it's usually right. But is it convincing as applied to the recruitment and propaganda efforts of terrorist organizations? To their efforts on social media, which can dramatically amplify the capacity of speech in one place to cause violence elsewhere at some uncertain time? What if more speech doesn't work, and the result is that dozens, hundreds or thousands of people are killed?

True, there may be value in even the most extreme and hateful speech: At the very least, people can learn what other people believe. But it's fair to ask whether that benefit might be dwarfed by the cost, if those forms of speech create a genuine risk of large numbers of deaths. Hand himself argued that his narrow definition of incitement avoids subjectivity and overreach, and that it can't be abused by the government to silence dissenters and unpopular causes.

To minimize the danger to free speech, it might be best to combine Hand's approach with a form of balancing: If (and only if) people are explicitly inciting violence, perhaps their speech doesn't deserve protection when (and only when) it produces a genuine risk to public safety, whether imminent or not. That approach would essentially retain the high level of protection that is now given to political speech and dissent of all kinds.

Cass Sunstein is director of the Harvard Law School's program on behavioral economics and public policy.