Widely regarded as one of the masterpieces of medieval music and of all religious music, it is historically notable as the earliest complete setting of the Ordinary of the Mass attributable to a single composer (in contrast to earlier compilations such as the Tournai Mass).

The repeated phrase is “Kyrie, eleison” (or “Lord, have mercy”). It is usually (but not always) part of any musical setting of the Mass. Kyrie movements often have an ternary (ABA) musical structure that reflects the symmetrical structure of the text.

Machaut’s Messe de Notre Dame is, deservedly, the best-known composition of the entire age. Unique to this mass is the use of isorhythmic technique. Isorhythm is the repetition in a voice part, usually the tenor of an extended pattern of duration throughout a section or an entire composition.

The Kyrie melodies also have stylistic characteristics that are manifestly different from the musical settings of the Propers: transposition, episodic melodic material, motif repetition, and eventually signs of a strong influence exerted by the popular Sequence, Estampie, and Lai-Leich forms.

In the New Testament, Kyrie is the title given to Christ, as in Philippians 2:11. As part of the Greek formula Kyrie eleison (“Lord, have mercy”), the word is used as a preliminary petition before a formal prayer and as a congregational response in the liturgies of many Christian churches.

The four main vocal ranges are: Soprano – A high female (or boy’s) voice. Alto – A low female (or boy’s) voice. Tenor – A high (adult) male voice. Bass – A low (adult) male voice.

Guillaume de Machaut (sometimes spelled Machault; c. 1300–April 1377) was a medieval French poet and composer. Machaut helped develop the motet and secular song forms (particularly the lai and the formes fixes: rondeau, virelai and ballade).