Organum

Organum, first development of plainsong in early music from chant into a form of polyphony. The Greek word “organon” was understood as an “organ of the body”, a musical instrument such as the human voice, or a spiritual song of praise. By the time of the earliest polyphony it was a technical term either for a new vocal line (vox organalis) added to a pre-existing plainsong chant (vox principalis), or for the resulting two-part texture. In the 9th-century treatise Musica Enchiriadis “simple organum” referred to the consonant intervals produced by largely parallel motion at the intervals of a fourth, fifth, or octave. Further doubling at the octave to produce a three- or four-part texture was called “composite organum”. So as to avoid unsatisfactory dissonances such as augmented fourths, strict parallel motion was progressively abandoned resulting in “modified parallel organum”. This introduced new contrapuntal considerations and an increased awareness of harmony and cadence, as detailed in the Micrologus of Guido d'Arezzo around 1025.

With more sophisticated notation and improving performing skills came the ability to “compose” through improvisation, as seen in the second Winchester Troper (early 11th century) with its 53 melodic alternatives to a single vox organalis. By 1100 “free organum” was common with its more liberal choice of intervals, contrary motion, regular crossing of parts and cadential formulae. Two distinct forms of organum evolved: the old note-against-note style first called “diaphonia” and then “discant”, and a new style still carrying the name “organum” but now consisting of a melismatic line of notes above a single sustained note, as seen in manuscripts (late 11th to early 13th centuries) from the Abbey of St Martial in Limoges and the Codex Calaxtinus (c. 1170) housed at Santiago de Compostela.

The melismatic organum style flowered most expansively in the music attributed to Léonin and Pérotin and the cathedral of Notre Dame in Paris. Whereas earlier surviving collections of organum were not consistently liturgical, Léonin's Magnus Liber Organi (late 12th century) is an anthology of graduals, alleluias, and responsories selected for special feast days in the Church year. These two-part settings were revised by Pérotin probably around 1205 to introduce shortened substitute sections (clausulae) composed in the discant style that was then returning to fashion, and included elaborations into three or four parts.

By the mid-13th century three forms of organum were recognized by the theorist Johannes de Garlandia: the old sustained-note style still labelled organum; copula, using the sustained style but employing the newly developed modal rhythmic notation; and discantus, also featuring modal rhythm but in the newly revived note-against-note style. The future of Medieval music lay with discantus transported into the non-liturgical spheres of the conductus and motet, and organum soon became a term for the outmoded polyphony based on plainsong.