Aaron Copland (November 14, 1900 December 2, 1990) was an American composer of concert and film music. Instrumental in forging a uniquely American style of composition, he was widely known as "the dean of American composers." Copland's music achieved a difficult balance between modern music and American folk styles, and the open, slowly changing harmonies of many of his works are said to evoke the vast American landscape. He incorporated percussive orchestration, changing meter, polyrhythms, polychords and tone rows. Outside of composing, Copland often served as a teacher and lecturer. During his career he also wrote books and articles, and served as a conductor, most frequently for his own works.