Cantus is scored for mezzo-soprano, viola, and piano, and draws inspiration from organum and music from the Middle Ages. The chant constantly changes in timbral density and colour while low, bell-like interjections from the piano and viola interrupt its steady flow. The text of the vocal part is written entirely using the syllabic pitch names found in the solfège system. These Latin-derived syllables correspond with the pitches with which they are paired but sometimes use enharmonic equivalents. The total duration of the piece is around seven minutes.