Why did polyphony require more precise systems of rhythmic notation?

In the context of Western music, the development of polyphony—the simultaneous sounding of two or more independent melodic lines—made precise rhythmic notation an indispensable requirement.12

Before the emergence of polyphony, plainchant consisted of a single melodic line, which did not require a complex system to coordinate multiple voices. However, as composers began combining separate melodic entities, they needed a way to ensure the parts remained synchronized according to established rules of consonance. Without organized rhythm, multipart music would have remained limited to primitive stages of counterpoint.132

To achieve this coordination, musicians developed rhythmic modes, which were standardized patterns of short and long durations. These were initially indicated through ligatures—compound symbols grouping individual pitches—rather than individualized note shapes. As compositions grew in length and complexity, these systems evolved into more flexible, individual symbols for time values, eventually laying the foundation for modern musical notation.425