How did isorhythm organize the tenor part in 14th-century motets?

In 14th-century motets, isorhythm served as a structural organizing principle, primarily applied to the tenor part, which often functioned as a cantus firmus derived from plainchant.12

This technique organized the tenor through the systematic repetition of two distinct elements:

• Talea: A fixed rhythmic pattern that was extended throughout the composition.1
• Color: A melodic sequence that provided the pitch content.1

While these two patterns were often applied simultaneously, they did not always coincide in length; the rhythmic pattern (talea) could repeat multiple times over the course of a single melodic statement (color), or vice versa. By abandoning the rigid rhythmic modes of the 13th century, isorhythm allowed composers like Guillaume de Machaut to create complex, integrated musical structures that provided a stable foundation for the more florid upper voices. This systematic application of rhythm became a hallmark of the Ars Nova style, offering a way to unify compositions that were otherwise conceived in separate, loosely connected layers.2134