organum

Organum represents one of the earliest experiments in Western polyphonic music, emerging around the 9th century. In its simplest form, a second voice moves in parallel motion at a fixed interval — usually a fourth or fifth — below or above the original chant melody (the vox principalis). Over time, organum evolved from this rigid parallel movement to include oblique and contrary motion. By the 12th century at the Notre Dame school in Paris, organum had developed into elaborate compositions where the original chant notes were sustained as long pedal tones while florid upper voices wove intricate melodic patterns above them. This "melismatic organum" by composers like Pérotin could involve up to four independent voices and represents a quantum leap in musical complexity.