What is the primary characteristic of an organum?

The primary characteristic of an organum is that it is based on a cantus firmus. In the context of early music, particularly during the medieval period, organum refers to a style of polyphonic music that developed from Gregorian chant. The cantus firmus serves as a foundational melody, typically drawn from existing liturgical music, around which additional melodic lines are added. This technique allowed composers to create harmony and texture above the fixed chant, leading to the rich and layered sound characteristic of organum.

The use of a cantus firmus is central to the structure of organum, as it provides a stable point that guides the composition and development of the other voices, or parts, which often move in parallel motion or counterpoint. Understanding this concept is crucial for recognizing how early music conceptualized and developed polyphony, significantly influencing Western musical traditions.

Other choices may deal with specific aspects of music composition or instrumental performance, but they do not capture the essence of what defines organum as a genre.