Twentieth-Century Harmony: Creative Aspects and Practice by Vincent Persichetti

One of the most important books on contemporary music in the twentieth century.
The author examines the nature of intervals in various contexts, discusses the modes and other scales employed in modern music, describes the formation and uses of chords by thirds, by fourths, and by seconds, of added-note chords and polychords; he deals with different types of harmonic motion, with harmonic rhythm and dynamic sand ornamentation, with harmonic behavior in tonality, polytonality, atonality and serial composition.