What is the function of a descant in music?

The function of a descant in music is to act as a counter melody, which is precisely why the answer is correct. A descant is typically a melodic line that is complementary to the main melody, often sung or played at a higher pitch. It adds texture and complexity to the music, enhancing the overall sound without overshadowing the primary melody. This creates a richer musical experience, as the interplay between the main melody and the descant can evoke more emotional depth and interest.

In many choral settings, for instance, a descant might be introduced during the repetition of a refrain, providing a contrasting yet harmonious element that lifts the piece. This is distinctly different from simply providing rhythm, performing solo, or playing background music, as those functions do not specifically involve the creation of a complementary melodic line that characterizes a descant.