(from Lat. Ordinarium [missae et officii]).
Chants whose texts remain constant from day to day in the services of the Western Church, as distinct from those whose texts vary (Proper chants). Strictly the term applies to chants from both Mass and Office, but it is chiefly used to refer to the Kyrie, Gloria, Credo, Sanctus and Agnus Dei, the parts of the Mass Ordinary most frequently set polyphonically by composers from the second half of the 14th century onwards. The Ite missa est at the close of Mass, with choral response ‘Deo gratias’, has also been included in a few such settings (e.g. by Machaut). Although the texts of the chants do not vary, they have been influenced by the principle of variation for reasons of liturgical propriety, in that they are recommended, though not prescribed, to be sung to a small corpus of different melodies, each one for use on different occasions (double feasts, single feasts, feasts of the BVM etc.). In the Middle Ages, Ordinary chants for important feasts had trope texts which rendered them Proper in the liturgical sense.
For the transmission of Ordinary chants from the Middle Ages, see Kyriale, the name given to a collection of the chants. See also Mass, §I, 2, and separate articles on the chants mentioned above.