A 1949 United States Supreme Court case, instrumental in refining the doctrine of clear and present danger.

Father Arthur Terminiello, a Catholic priest, was invited by the Christian Veterans of America to address a rally of some 800 people. He gave a vitriolic anti-semitic speech, stating that the Communists and Jews would be America's downfall and that Hitler's actions were justified. Terminiello's views were well-known, and the war was still fresh in people's minds. A crowd of over 1000 people gathered outside the auditorium in protest, and ultimately turned violent, throwing bricks through the auditorium windows.

Terminiello was arrested and charged with causing a breach of the peace, in violation of a city ordinance. The trial court was instructed that "misbehavior may constitute a breach of the peace if it stirs the public to anger, invites dispute, brings about a condition of unrest, or creates a disturbance." The defendant did not take exception to this, but he held that the ordinance violated his right to free speech. However, by the precedent of Schenck v. United States, such a violation is permitted when the speech constitutes a clear and present danger. The court judged Terminiello's oratory to be equivalent to shouting "fire" in a crowded theater, and convicted him.

The conviction was upheld in appelate and state supreme courts, only to be overturned in a 5-4 decision at the federal level. In the decision, William O. Douglas states:

...a function of free speech under our system of government is to invite dispute. It may indeed best serve its high purpose when it induces a condition of unrest, creates dissatisfaction with conditions as they are, or even stirs people to anger... That is why freedom of speech, though not absolute... is nevertheless protected against censorship or punishment, unless shown likely to produce a clear and present danger of a serious substantive evil that rises far above public inconvenience, annoyance, or unrest.