What is the definition of Isorhythm in music?

Isorhythm is defined as a compositional technique that involves a recurring rhythmic pattern (the "color") that is combined with a varying melodic line (the "talea"). Specifically, it features a fixed sequence of rhythms that can be paired with different melodies. This form is notable in medieval music, especially in motets of the Ars Nova period.

The concept emphasizes the relationship between rhythm and melody, where the rhythmic pattern remains constant while the melodic component shifts, allowing for a complex interplay between these two musical elements. This enriches the texture of the music and creates unique phrases as the melody progresses over the repeated rhythmic framework.

In contrast, the other options do not accurately reflect the nature of isorhythm. A repeated melodic line through a piece is more indicative of techniques like ostinato or thematic development. Polyphonic texture refers to the simultaneous combination of different melodic lines, which is broader than the specific rhythmic focus of isorhythm. Lastly, composing in major scales does not relate to the rhythmic structure at the heart of isorhythm but refers more generally to a mode of composition.