organum purum

Organum is an early form of polyphonic music that emerged in the Middle Ages, evolving from Gregorian chant. Initially, it involved adding a second voice, often moving in parallel motion at a fourth or fifth below the original chant (the vox principalis). This practice, described in Musica enchiriadis around 900 CE, marked a significant departure from monophonic music.123

More elaborate forms developed, such as organum purum, where a florid, freely composed melody (duplum) was sung above a sustained chant (tenor). Composers like Léonin and Pérotin, associated with the Notre Dame school in Paris, further developed organum into complex two-, three-, and four-part compositions, setting chant melodies for liturgical music. This innovation laid the groundwork for centuries of polyphonic music in Western tradition.214