Clausulae

The term is employed mainly for a large repertory of polyphonic compositions of the late 12th and early 13th centuries (school of Notre Dame) that are based on a short fragment of a Gregorian chant, in contrast to the organa, which are based on the entire chant.  They are relatively short compositions, invariably based on a melisma of a responsorial chant.  Accordingly, there is no full text in the tenor of a clausula, but only one or two words or sometimes only a syllable to indicate from which chant the tenor is borrowed.  Many such clausulae (well over 500; about a dozen in 3 parts, the others in 2) are preserved in the sources of Notre Dame.  They were probably intended to serve as substitutes for the corresponding sections in the organa of Leonin.

Most of the early motets are directly derived from clausulae, retaining their music but underlaying a full text to the upper part.