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.