POSTLUDE

The rise of polyphony in the Middle Ages parallels in many ways the development of monophonic song, including plainchant. It began as a manner of performance, became a practice of oral composition, and developed into a written tradition. Much of its history is hidden from view and can only be reconstructed partially from the traces that remain — chiefly descriptions in treatises and notated examples. But what was written down was only a small part of the polyphony that was sung.

The Notre Dame repertory gradually expanded through the process of troping, whereby combinations of new melodies and texts were added to, or layered above, the original monophonic lines. By the late twelfth and early thirteenth centuries, organum and motet were well-established genres in which musicians elaborated on chant tenors. Organum evolved from parallel types (where added voices merely duplicated the contour of the chant melody) to more-florid pieces (where the added voices assumed greater melodic and rhythmic independence from the cantus firmus). Sections of discant-style organa, called clausulae, became separate works and, with added texts, gave rise to the motet, a new genre that dominated the polyphonic scene in France by the mid-thirteenth century.

These genres and conventions were soon to be outmoded, however, because of newer motet styles. The rhythmic modes gradually became obsolete, and the chant tenor was relegated to a purely formal function, elevating the triplum to the status of a solo voice against the accompanying lower parts. The road was open to a new musical style, a new way of composing (Ars Nova) in an age that looked back on the music of the latter half of the thirteenth century as the antique, outdated way (Ars Antiqua).