Missa Brevis Orbis Factor is a setting of the Mass ordinary (Kyrie, Sanctus-Benedictus, and Agnus Dei) for a cappella SATB choir, built on the Gregorian chant of Mass XI (“Orbis Factor”). The title translates as “creator of the world,” and I have always been fond of the tune for its dramatic leaps.

This work belongs to a period in which I worked closely with chant, and its method is contrapuntal throughout: in each passage a single voice carries the chant tune in steady quarter notes — longer on the held episema notes — while the other voices spin counterpoint around it in dotted figures and running eighths. The chant migrates from voice to voice, the sections feathered and dovetailed, so the music flows as a continuous web of line. Organ doubling is optional.

The Kyrie opens in C minor. The altos sing the first Kyrie chant tune, with its recognizable plunging fifth, while the other voices gradually add contrapuntal detail. The sopranos intone the Christe chant, with its distinctive ascending fifth, while again, the other voices provide moving notes and additional harmonies. The basses take the final Kyrie, with its ascending fourth and melismatic flourish, which I kept intact. An imitative figure on repeated utterances of eleison conclude the movement on an open C chord.

In the Sanctus (“Holy”), the altos intone the first two exclamations while the sopranos take the third. The tenors carry the chant tune at Pleni sunt caeli et terra (“heaven and earth are full”), the other voices entering one by one to a great crescendo on gloria tua (“your glory”) in C minor. The upper three voices repeat the phrase in C major, cadencing again on an open C chord. The first Hosanna breaks the prevailing legato, marked lo stesso tempo, poco marcato. The basses take over the cantus beneath the upper voices’ high, running eighths.

After a brief pause, the texture lightens for the Benedictus (“blessed”), the altos singing the chant while tenors and sopranos dance around it. The recap of the Hosanna gives the upper three voices the same music, harmony, and words as the before, but with a twist. Now the basses, freed from the chant tune, weave their own counterpoint into the other voices, so the repeat sounds newly active and alive. A final Hosanna in excelsis cadences deceptively in F major.

The Agnus Dei, marked adagio e sostenuto, descends to F minor, slow and solemn. The tenors carry the first Agnus cantus, with the altos and basses joining in. The sopranos are held back until miserere nobis (“have mercy on us”). The altos take the second Agnus tune in the same three-voice texture borrowed from the Benedictus. The final Agnus gives the chant to the sopranos, the full choir entering forte with a subito mezzo-piano at qui tollis (“who takes away”). The texture thins to the tenors alone on the last mundi, then thickens with surprising speed. Voices build to a fortissimo five-part dona nobis pacem (“grant us peace”). The phrase repeats, a G-flat shading the harmony, before dimming through long-held fermatas, marked lunghissime with each voice part marked dolcissimo. The Mass comes to a slow, settling rest at the final pacem (“peace”) on a warm, six-part A-flat major chord.

The audio sample is the opening of the Kyrie. Here are the Latin and English texts: