Organum

   Earliest known type of Western polyphony. Anonymous treatises dating from the second half of the ninth century describe the addition of a new melody, the vox organalis ("organal voice") to a traditional Roman Catholic chant melody, the vox principalis. The new melody is a near copy of the chant but sung at the interval of a perfect octave, fourth, or fifth, note against note. Other intervals may be used to begin and end the organum on a unison. Early 12thcentury sources indicate more melodic independence in the vox organalis, but always homorhythmic, note against note.

   A decisive break for rhythmic independence of the combined melodies occurs in manuscripts associated with the Abbey of St. Martial, Limoges, Toulouse, and Narbonne in southern France, dating from the 12th century. For originally syllabic chants, they show a melismatic organum, a precursor of the cantus firmus technique, in which the traditional chant is sustained in long tones under a florid countermelody, and for originally melismatic chants another type, in which one, two, three, or four notes of the new melody sound against one (or sometimes more than one) note of the chant. Thirteenthcentury theorists distinguished these as organum purum and discant. Sources indicate advanced and prolific composition in polyphony associated with the cathedral of Notre Dame in Paris from the latter half of the 12th century. The melismatic organa pura attributed to Leoninus are rhapsodically long. Clausulae (discant organum) attributed to Perotinus employ as many as four voices. In the 13th century, the genre gives way to motet and conductus.