O Antiphons

The O Antiphons, also known as The great Os are Magnificat antiphons used at Vespers of the last seven days of Advent in Western Christian traditions. They are also used as the alleluia verses on the same days in the Catholic Mass.

They are referred to as the "O Antiphons" because the title of each one begins with the interjection "O". Each antiphon is a name of Christ, one of his attributes mentioned in Scripture. They are:

In the Roman Catholic tradition, the O Antiphons are sung or recited at Vespers from December 17 to December 23 inclusive. Some Anglican churches (e.g. the Church of England) also use them, either in the same way as modern Roman Catholics, or according to a medieval English usage (see below).

Antiphon

An antiphon (Greek ἀντίφωνον, ἀντί "opposite" and φωνή "voice") in Christian music and ritual is a responsory by a choir or congregation, usually in the form of a Gregorian chant, to a psalm or other text in a religious service or musical work.

Antiphony is now generally used for any call and response style of singing, such as the kirtan and the sea shanty. Antiphonal music is music that is performed by two semi-independent choirs in interaction, often singing alternate musical phrases.Antiphonal psalmody is the singing or musical playing of psalms by alternating groups of performers. An antiphony is also a choir-book containing antiphons.

Origins

The 'mirror' structure of Hebrew psalms renders it probable that the antiphonal method was present in the services of the ancient Israelites. According to the historian Socrates of Constantinople, antiphony was introduced into Christian worship by Ignatius of Antioch (died 107), who saw a vision of two choirs of angels.

Antiphons have remained an integral part of the worship in the Byzantine and Armenian Rite. The practice was not found in the Latin Church until more than two centuries later. Ambrose and Gregory the Great, who are known for their contributions to the formulation of Gregorian chant, are credited with 'antiphonaries', collections of works suitable for antiphon, which are still used in the Roman Catholic Church today.