(from Lat. Proprium [missae et officii]).
Chants whose texts vary from day to day, as distinct from those whose texts remain constant (Ordinary chants). Strictly the term applies to chants from both Mass and Office, but it is customary to use the term chiefly to refer to Mass chants, owing to the need for terms that distinguish between those parts of the Mass most often set polyphonically from the second half of the 14th century onwards (the Ordinary), and those usually sung as plainchant. Nevertheless, there are settings of cycles of Proper chants by, for example, composers of the Notre Dame School (see Magnus liber), Isaac and Byrd.
The Proper chants of the Mass are the introit, gradual, alleluia, tract, offertory and communion. The sequence, sung throughout the Middle Ages on important feast days, may also be included in this category, as may also tropes, adjuncts to the above group of chants, which were always Proper to a particular feast. The principle of varying chants for reasons of liturgical propriety also affects the unvarying texts of the Ordinary (Kyrie, Gloria etc.) in that they may be sung to a small corpus of different melodies, each one for use on a different occasion (double feasts, single feasts, feasts of the BVM etc.).
See also Mass, §I, 2(iii).