How do monophonic and polyphonic vocal music differ?

In the context of vocal music, the primary difference between monophony and polyphony lies in the number of melodic lines performed simultaneously.

Monophony
Monophony consists of a single, unaccompanied melodic line. It is a fundamental element of many musical traditions, with early examples including Byzantine and Gregorian chants. In a monophonic texture, there is no harmonic support or secondary melody; the focus remains entirely on the single voice part.12

Polyphony
Polyphony involves the simultaneous combination of two or more independent melodic lines. Derived from the Greek for "many sounds," this texture allows each voice to maintain its own melodic identity while weaving together with others. In Western music, this is often achieved through counterpoint, where distinct lines are rhythmically and melodically differentiated. While monophony focuses on a singular line, polyphony creates a complex "web" of sound, ranging from simple two-part organum to dense arrangements featuring dozens of independent voices.324

These textures are not mutually exclusive, and composers have historically varied them within the same musical work to achieve different aesthetic effects.3