In this U.S. Supreme Court decision, the Court announced the "incitement test" to determine when a speaker can be punished for speech or expression that encourages others to break the law. Speech can be punished as incitement when it:
This standard, still in use today, sets a very high constitutional hurdle to clear. The speech must be intended to cause and likely to produce unlawful behavior imminently—meaning right now, not tomorrow, next week, or next year. Absent proof of this purpose and effect, the speech can't be punished as incitement.