The clausula (Latin for "little close” or “little conclusion"; plural clausulae) was a newly composed section of discant ("note against note") inserted into a pre-existing setting of organum. Clausulae flourished in the late twelfth and thirteenth centuries and were associated with the Notre Dame school. The origin of the clausula has long been subject of scholarly debate, as the relationship between clausulae and motets is very complicated. Clausulae eventually became used as substitutes for passages of original plainchant. They occur as melismatic figures based on a single word or syllable within an organum. Origins Clausulae emerged from the compositional practices of the Notre Dame school in Paris c. 1160–1250 (during the stylistic period known as ars antiqua). The composers Léonin and Pérotin in particular contributed heavily in composing clausulae. Rather than write entirely new music, the preference was to take existing music, that is, plainchant melodies, and develop or improve upon them. According to an English author known as Anonymous IV (c. 1280), "Pérotin was better at making clausulae than Léonin had been in that Pérotin was better at making better discant style of clausulae." The appearance of clausulae provided the first rhythmic system. (It is hard to find rhythmic notation in the earliest motets because of the lack of the use of clear rhythmic notation in the manuscripts.) Pérotin's clausulae make use of the rhythmic modes, whose strict metrical feet necessitated that voices change notes together (discantus). This was in contrast to the earlier practice of one voice moving in a free rhythm above a "tenor" voice (Latin tenere: "to hold") sustaining the long notes of a cantus firmus. The tenor line was often repeated to allow for expansion of the clausula; this was the origin of the technique known as isorhythm. The scholarly debate over the origin of the clausula continues. However, the term clausula already used in ancient Roman rhetoric, where it denoted "a rhythmic figure used to add finesse and finality to the end of a sentence or phrase." In particular, rather than seeing clausula as a genre, the part composed in the style of discantus with a definite final cadence was called clausula. Thus, there are more studies that relate specifically to the motet, rather than studies of the origin of the clausula. One scholar writes that "the motet arose through the addition of Latin texts to the melismatic upper voices of the two-voice clausulae