What is cantus firmus?

• A. A fixed melody used as the basis for a polyphonic composition
• B. A rhythmic drum pattern used in African music
• C. The leader's line in an ensemble
• D. A spontaneous improvised line in jazz

Answer: (A)

A cantus firmus is a fixed melody that serves as the structural spine of a polyphonic work. In medieval and Renaissance music, composers took a pre-existing tune—often a plainsong chant—and built additional voices around it, typically using longer note values and slower motion to keep the cantus firm in its melodic contour. This fixed melody acts as the unchanging anchor, while the other voices weave counterpoint above or around it, creating the rich textures of the piece. The term literally means “fixed song” in Latin, underscoring its role as the stable foundation of the composition. It isn’t about rhythmic patterns, leadership in the ensemble, or improvisation, which distinguishes it from those other musical practices.