Early polyphonic setting of plainchant (see Gregorian chant), the earliest form of counterpoint. The oldest written organum (c. 900), which evidently reflects a prevailing improvisational practice, consists of two lines moving simultaneously, note against note, the added line often paralleling the chant line a fourth or a fifth below. Later the added line acquired greater melodic individuality and independence. Organum consisting of more than one note against each chant note (florid or melismatic organum) appeared by the early 12th century. Three- and four-voice organum were first composed by the Notre-Dame school. Organum died out with the advent of the 13th-century motet.
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