Hans Kelsen, (born Oct. 11, 1881, Prague, Bohemia, Austria-Hungary [now in Czech Republic]—died April 20, 1973, Berkeley, Calif., U.S.), Austrian-American legal philosopher, teacher, jurist, and writer on international law, who formulated a kind of positivism known as the “pure theory” of law.Kelsen was a professor at Vienna, Cologne, Geneva, and the German university in Prague. He wrote the Austrian constitution adopted in 1920 and served as a judge of the Austrian Supreme Constitutional Court (1920–30). After immigrating to the United States in 1940, he taught at Harvard, the University of California at Berkeley, and the Naval War College, Newport, R.I.Kelsen’s