sentences:  The Tournai Mass comprises six movements, each of which is for three voices.Because of the wide disparities in style and notation, and because no underlying musical structure (such as a common cantus firmus or parody procedure) has been noted between the mass movements, the Tournai Mass is believed to have been composed independently by several musicians over a period of fifty or more years, and was later compiled by a scribe to be performed as a whole.The first known mass to have been conceived of and composed as a single unified work is the Messe de Nostre Dame by Guillaume de Machaut, who probably knew the Tournai Mass and may have used it as a model.