According to Anonymous IV, Pérotin made revisions to Léonin’s Magnus liber organi. The extent of these revisions is apparent in the two-part organa in three manuscripts, W₁, F, and W₂. The pieces contained in all three sources are generally considered to form the body of the original Magnus liber organi. However, while all three have many pieces in common, each also contains clausulae not found in the others. This conflicts with Anonymous IV’s account that Pérotin abbreviated Léonin’s Magnus liber organi. Thus, all of these manuscripts represent enlarged forms of the Magnus liber organi, and also show different stylistic developments, particularly in the clausulae. Additionally, the total body of new organa nearly doubles the size of the collection’s original form. The additions to the Magnus liber organi show the extent of the technique of “Tenortausch,” the replacement of tenor melismas with melismas of other, related tenors contained within the same manuscript. This technique is evident in a large selection of pieces, primarily the Alleluia settings.

Index Classifications: Polyphony to 1300

Contributed by: Elizabeth Stoner