De harmonica institutione

De harmonica institutione is a treatise by the medieval French scholar and music theorist Hucbald. Written around the late 9th or early 10th century, it describes the gamut, which is the series of recognized musical notes, and the eight musical modes. Hucbald was a pupil of Milo of Saint-Amand and spent his life teaching. While he is credited with this work, some scholars suggest that other theoretical writings, such as Musica enchiriadis, may have been authored by a different, later writer known as Pseudo-Hucbald.1