MAGNUS LIBER ORGANI

(Lat. "Great Book of Organum")

Collection oforganumassociated with the cathedral of Notre Dame inParisand believed to have been composed between 1160 and 1225. No manuscript with the title exists; the collection has been reconstructed on the basis of later collections containing the repertory described by a 13th-century English student known as Anonymous IV, who citesLeoninusandPerotinusas the principal composers. This reconstruction contains 35responsoriesand 12 settings of theBenedicamus Dominofor thedivine office, and 20 Graduals and 40Alleluiasfor themass. There are also 500clausulaethat may be substituted for portions of themelismaticorganum with the same text. In most cases, thepolyphonyis intended to be sung in alternation with traditionalchant, which completes arespondor supplies a verse.

See alsoAlternatim.