Three contexts of meaning are associated with the term cantus firmus (Latin, also: cantus prius factus; Italian canto fermo, “fixed/enduring/unadorned song”). By the Middle Ages, in monodic sacredmusic, it had already come to denote a melody that advanced in tones of equal duration. As polyphony developed, cantus firmus also came to refer to a pre-existing melody that formed the basis for a composition. The term also occurs in a blend of both senses in music theo…