In Classical music, motet is a word that is applied to a number of highly varied choral musical compositions.
The name comes either from the Latin movere, ("to move") or a Latinized version of Old French mot, "word" or "verbal utterance." The Medieval Latin for "motet" is motectum, and the Italian mottetto was also used. If the word is from Latin, the name describes the movement of the different voices against one another.
According to Margaret Bent (1997),
"a piece of music in several parts with words" is as precise a definition of the motet as will serve from the 13th to the late 16th century and beyond. This is close to one of the earliest descriptions we have, that of the late 13th-century theorist Johannes de Grocheio.
Grocheio believed that the motet was
not intended for the vulgar who do not understand its finer points and derive no pleasure from hearing it: it is meant for educated people and those who look for refinement in art. 
The earliest motets arose, in the thirteenth century (Bent, 1997), out of the organum tradition exemplified in the Notre Dame school of Léonin and Pérotin. The motet probably arose from clausula sections, usually strophic interludes, in a longer sequence of organum, to which upper voices were added. Usually the clausula represented a strophic sequence in Latin which was sung as a discant over a cantus firmus, which typically was a plainchant fragment with different words from the discant. The motet took a definite rhythm from the words of the verse, and as such appeared as a brief rhythmic interlude in the middle of the longer, more chantlike organum.
The practice of descant over a cantus firmus marked the beginnings of counterpoint in Western music. From these first motets arose a medieval tradition of secular motets. These were two or three part compositions in which several different texts, sometimes in different vernacular languages, were sung simultaneously over a Latin cantus firmus that once again was usually adapted from a passage of Gregorian chant. It is suspected that, for the sake of intelligibility, in performance the cantus firmus and one or another of the vocal lines were performed on instruments. Among the trouvères, Robert de Reins La Chievre and Richart de Fournival composed motets.
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