. During the 12th century, improvised and composed or notated vocal polyphonic music began to take on a distinct stylistic change that ultimately divided it into two types. In discant, one or more parts were added mostly note-against-note to a plainchant melody, possibly moving in parallel motion but often in contrary motion with it; in organum, one part embellished with many notes each note of the plainchant, thus slowing it down considerably and making it, at its most ornate, unrecognizable. The limitation to which organum, described as an “infinitely flexible” art, was subject was that there could be but one performer of the added part, and therefore it would have been impossible to coordinate adequately between two or more singers. Organum was an almost perfect medium for virtuoso solo singing and improvising, in contrast to discant, in which interaction among singers (one to a part), a sense of ensemble, was the primary requirement. The singer of the plainchant played a role of support by sustaining each note of the chant until he coordinated the next one with the soloist, and organum that survives in notation is always in score so that the correlation of the two parts can more readily be seen.
These two different styles of polyphony, discant and organum, were nevertheless generically called “organum,” and thus the polyphony for the Graduals, Alleluias, and Responsories of the Notre-Dame repertory are termed “organa,” including the organa for three and four parts. Theorists of the 13th century who discussed “measurable music” (musica mensurabilis) divided this generic organum into three categories, most often discant, copula, and organum, the last being called organum purum or organum in speciali. These are not three types of pieces of music, however, but the three styles or musical textures that could be found within the polyphony for a Gradual, Alleluia, or Responsory. In time, genres became categorized as species of discant—e.g., the motet—and there seem to be such ties between copula and hocket that need further elucidation.
The Magnus liber organi for the cathedral of Notre-Dame in Paris was, in its original form, apparently mostly in organum style, since its compiler, Léonin, was called optimus organista. Léonin’s successor Pérotin, called optimus discantor, possibly revised much of the Magnus liber organi, replacing many of the passages in organum style with discant; and he composed the two known organa quadrupla, which were for the Graduals of the Masses of Christmas and the feast of St. Stephen of the day following. These organa are in discant style, because the three embellishing parts are rhythmically and melodically coordinated in the manner of discant.
Atkinson, Charles M. “Franco of Cologne on the Rhythm of Organum purum.” Early Music History 9 (1989):1–26.
Reckow, Fritz. “Das Organum.” In Gattungen der Musik in Einzeldarstellungen, Gedenkschrift Leo Schrade. Bern: Francke, 1973, pp. 434–96.
Roesner, Edward H. “The Performance of Parisian Organum.” Early Music 7 (1979):174–89.
Sanders, Ernest H. “Consonance and Rhythm in the Organum of the 12th and 13th Centuries.” Journal of the American Musicological Society 33 (1980):264–86.
Yudkin, Jeremy. “The Rhythm of Organum Purum.” Journal of Musicology 2 (1983):355–76.
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