Léonin (active ca. 1165-1185), or Leoninus, of the Cathedral of Notre Dame in Paris, is the earliest known composer of polyphonic art music and the creator of controlled rhythm and meter, as well as of the earliest notation to convey rhythm.
About the life of Léonin absolutely nothing is known. His name is mentioned in a treatise, actually class notes taken at lectures an anonymous English student attended at the University of Paris about a century later, in the 1270s. In this treatise Léonin is connected with Paris and is praised as the best composer of organa (two-voiced settings of soloistic portions of chants of the Mass and the daily prayer hours).
Léonin evidently composed his organa for the Cathedral of Notre Dame, whose present magnificent stone structure rose in the main between 1163 and 1208. It has been suggested that he was a choirboy first and later became the master of the choirboys. This would account for the diminutive of Léo by which he was known and also for the absence of his name from the preserved list of the higher officers of the Cathedral.
Léonin's works may be called the cradle of Western art music. His organa are arranged for two vocal lines. One is the chant tune, the cantus firmus, laid out either in notes of undefined length or, in some sections, in a sequence of definite note values; the other is a newly composed melodic descant, a rhythmically controlled coloratura of great ingenuity, coordinated with the cantus firmus. Although organa had existed for some time before Léonin, the separation of these two styles, the "pure organum"—with long chant notes—and what was then called "discant," where both voices have strict rhythm, was his creation. So was the notation he used to symbolize this rhythm, the "modal notation," which laid the basis for musical notation as we know it. Moreover, his works constitute the first comprehensive repertoire of liturgical polyphony, which, with settings for about 100 Gregorian chants for all the major feasts of the Church year, remained in use for more than 2 centuries and spread to all the Western countries. This repertoire formed what the anonymous English student called the Magnus liber organi (Great Book of Organa); it became a widely imitated model.
Léonin also created a second species of polyphonic music, the conductus, a processional song. Monophonic conducti as well as sporadic two-part settings had existed before Léonin, but he established the polyphonic species firmly. Conducti are Latin songs, covering a wide range of contents—religious, political, lyrical, convivial— sometimes heard at Church and sometimes at performances of liturgical dramas, processions, banquets, and private occasions. The poetic texts are stanzaic, in strict rhythm, and sung more or less one note to each syllable, with both voices moving in essentially the same rhythm, though at verse and stanza ends and beginnings cadenzalike duet passages of many notes are often sung to a single syllable.
The best survey of Léonin's works is in Donald Jay Grout, A History of Western Music (1960). Much of Léonin's music is available in modern transcription in William Waite, The Rhythm of Twelfth-Century Polyphony, and a few works have been recorded.