Credo

A credo (pronounced [ˈkɾeːdoː], Latin for "I Believe") is a statement of religious belief, such as the Apostles' Creed. The term especially refers to the use of the Nicene-Constantinopolitan Creed (or less often, the Apostles' Creed) in the Mass, either as spoken text, or sung as Gregorian chant or other musical settings of the Mass.

After the formulation of the Nicene Creed, its initial liturgical use was in baptism, which explains why the text uses the singular "I ...." instead of "we...." The text was gradually incorporated into the liturgies, first in the east and in Spain, and gradually into the north, from the sixth to the ninth century. In 1014 it was accepted by the Church of Rome as a legitimate part of the Mass. It is recited in the Western Mass directly after the Homily on all Sundays and Solemnities; in modern celebrations of the Tridentine Mass as an extraordinary form of the Roman Rite, the Credo is recited on all Sundays, feasts of the I class, II class feasts of the Lord and of the Blessed Virgin, on the days within the octaves of Christmas, Easter, and Pentecost, and on the "birthday" feasts of the apostles and evangelists (including the feasts of St. Peter's Chair and of St. Barnabas). It is recited in the Eastern Liturgy following the Litany of Supplication on all occasions.

Probably because of its late adoption, and the length of the text (the longest in the Ordinary of the Mass), there are relatively few chant settings of it. What is identified as "Credo I" in the Liber Usualis was apparently widely considered the only authentic Credo, and it is the element of the ordinary that was most strongly associated with a single melody. The Liber Usualis contains only two other settings, designated as "Credo V" and "Credo VI," which is far fewer than for other settings of the Ordinary.

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