Cantus Firmus: translation
(Lat. "fixed chant")
Compositional technique whereby the composer takes a preexisting melody, usually from the traditional repertories of Gregorian or medieval chant, Lutheran chorales, etc., and sets it in long durations (determined by him) while composing original counterpoint to accompany it. The technique originated in the melismatic organum of southern France in the 12th century and in the discant organum of the so-called Notre Dame school (c. 1160–c. 1225). The voice singing the traditional chant melody, called "tenor" from the Latin tenere "to hold," already has the comparatively long durations and the repetitions of the melody that would come to mark the classic technique.Repeating, often isorhythmic tenors were the foundation of virtually all motets and polyphonic masses until the turn of the 16th century when structural imitation and polyphonic parody replaced the cantus firmus. Throughout this period, the tenor voice was the most common location of the cantus firmus, but it might wander among the upper voices in some pieces. In Baroque compositions, it may be found in any voice.
The virtues of the technique are its repetition, its sustained tones, and its origin in tradition.
Its repetition allows a texture of fast rhythm to be extended for far longer duration than it could have otherwise sustained, an essential advantage in medieval polyphony. Repetition also unifies the composition perceptually while allowing creativity and change in the added contrapuntal voices. Composers often increased the speed of the repetitions in carefully chosen symbolic proportions (e.g., the motet Nuper rosarum flores of Guillaume Du Fay).
The sustained quality of the cantus firmus produces a subtle musical tension based on the disparate speeds in the texture. The composition cannot end until the voices match up. For this reason, when the cantus firmus repeats at proportional speeds it is almost always a faster proportion, never slower, in order to facilitate the matching. The use of a traditional, known melody instantly assures a semantic reference for all those who know it. For this reason, Josquin Despres employs a chant from the Requiem mass in his famous {}Nymphes des Bois, the lament on the death of Johannes Ockeghem (c. 1497). Chorale cantatas and chorale preludes from the Lutheran tradition take advantage of the same principle. Ludwig van Beethoven uses a chant melody in the Credo of his Missa Solemnis in 1823, when few would have recognized it, because by then the sound of one slow voice against a fast texture was so singular that it had become, like choral fugues, part of the sacred semantic.