The composer Arnold Schoenberg (1874–1951) wrote pieces which were atonal (meaning that they did not sound as if they were in any clear musical key). Later, Schoenberg invented a new system for writing music called twelve-tone system. Music written with the twelve-tone system sounds strange to some, but is mathematical in nature, often making sense only after careful study. Pure twelve-tone music was popular among academics in the fifties and sixties, but some composers such as Benjamin Britten use it today, when it is necessary to get a certain feel.