What is a notable characteristic of organum?

The notable characteristic of organum is that it represents an early form of polyphonic music. Originating in the medieval period, organum involves the addition of one or more melodic lines to an existing plainchant, or Gregorian chant. This layering of melodies creates a richer texture, marking a significant development in the history of Western music.

Unlike earlier monophonic chant, where a single melody was sung without any harmonic support, organum introduces harmony through the simultaneous sounding of multiple melodies. This technique laid the groundwork for more complex forms of polyphony that would evolve in later centuries. The innovation of organum illustrates a pivotal moment in music history, showcasing the shift towards more elaborate musical structures and the exploration of vocal harmony.

The other options do not accurately capture the essence of organum. For instance, while some pieces may be instrumental, organum is primarily rooted in vocal music, specifically the adaptation of chant. Although harmonic progressions may develop later in music history, organum itself is focused on the layering of voices rather than specific harmonic changes. Additionally, while the solo vocal tradition is important, organum is characterized by its polyphonic nature, which directly contrasts with solo singing.