What is the clear and present danger test?

“Clear and present danger” was the standard Justice Oliver Wendell Holmes announced in Schenck v. United States (1919) for deciding when the First Amendment allows the government to punish speech: the question, he wrote, is whether the words used create a clear and present danger that they will bring about substantive evils Congress has a right to prevent — famously illustrated by his example of falsely shouting fire in a crowded theater. For decades the test gave the government considerable room to restrict speech seen as politically dangerous, including in cases upholding convictions for distributing anti-draft pamphlets and, later, for advocating communist revolution. That changed with Brandenburg v. Ohio (1969), which involved a Ku Klux Klan leader convicted under Ohio's criminal syndicalism law for a speech advocating vaguely threatening political action. The Supreme Court unanimously overturned the conviction and, without using the old phrase directly, replaced it with a much narrower two-part standard: the First Amendment does not permit a state to forbid advocacy of force or law violation “except where such advocacy is directed to inciting or producing imminent lawless action and is likely to incite or produce such action.” The shift matters because it separates advocating an idea, even a radical or violent one in the abstract, from actually inciting a specific, imminent act — under Brandenburg, speech has to cross both thresholds (intent to incite immediate lawlessness, and a real likelihood it will succeed) before it loses First Amendment protection. Brandenburg's imminent-lawless-action test remains the controlling standard for incitement cases today, having effectively retired the looser Schenck-era clear-and-present-danger language.