Clear and present danger is a term used by Justice Oliver Wendell Holmes, Jr. in the unanimous opinion for the case Schenck v. United States,<1> concerning the ability of the government to regulate speech against the draft during World War I:
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 that they will bring about the substantive evils that the United States Congress has a right to prevent. It is a question of proximity and degree. When a nation is at war, many things that might be said in time of peace are such a hindrance to its effort that their utterance will not be endured so long as men fight, and that no Court could regard them as protected by any constitutional right.
Following Schenck v. United States, "clear and present danger" became both a public metaphor for First Amendment speech<2><3> and a standard test in cases before the Court where a United States law limits a citizen's First Amendment rights; the law is deemed to be constitutional if it can be shown that the language it prohibits poses a "clear and present danger". However, the "clear and present danger" criterion of the Schenck decision was later modified by Brandenburg v. Ohio,<4> and the test refined to determining whether the speech would provoke
an imminent lawless action.http://en.wikipedia.org/wiki/Clear_and_present_danger