«TE DEUM». — Also called the Hymnus ambrosianus or Hymnus S. Trinitatis, it is a solemn hymn of praise and thanksgiving in honor of the Most Holy Trinity. It consists of two parts with an addition of eight psalm-like verses. The first part («Te Deum... confitetur Ecclesia»: 1–10; «Patrem... Spiritum»: 11–13) comprises a praise of the Father followed by a kind of Trinitarian doxology. The second («Tu rex... numerari»: 14–21) is a Christological praise. The eight added verses were detached from the «Gloria in excelsis», where they were originally united, and derive from: vv. 22 and 23 from Psalm 27:9; vv. 24 and 25 from Psalm 144:2 (from the Roman version); V. 26 is a morning verse, which also recurs in the canonical hour of «Prime»; V. 27 derives from Psalm 122:3; V. 28 from Psalm 32:22 and V. 29 from Psalm 30:2.
The T. D. does not appear to be an original composition; hence it is more properly spoken of as a compilation than as an authored work. Indeed, the first part is the oldest and derives from an anaphora: it includes the biblical Trisagion in a liturgical form, and cites the Prophets (from the early Christian centuries).
After the Apostles, only martyrs are mentioned, not confessors; vv. 7–9 seem to come from Cyprian (De mortalitate, ch. 26). An ancient Greek version exists of the first part (vv. 1–10). The second part, with its Christological praise, corresponds well to the 4th century and the beginning of the 5th, as the rules of the «cursus» observed there (more than in the first part) indicate the time of composition as the 4th–5th century. The psalm-like verses point to a time before 389, the era of St. Jerome’s revision.
Recently, in comparison with a group of Greek evening hymns, Baumstark has indicated a very ancient type of hymns, among which the T. D. might fittingly be included. A very charming legend attributes its composition to SS. Ambrose and Augustine; but this dates only from the 12th century. SS. Hilary, a Sisibutus, and an Abbondius are also mentioned as possible authors. In the oldest manuscripts the T. D. is without attribution. With valid arguments, Morin proves that its author is Nicetas of Remesiana ([v.], d. after 414); though this is not without contradiction. The T. D. was known in the 5th century in the monastic island of Lérins, from where SS. Caesarius (in 489–98 at Lérins) and Aurelian of Arles prescribed it, not in their Rules for Sundays. From Lérins, where it was in use c. 415–20, St. Patrick may have brought the T. D. to Ireland on his return in 432; indeed, the Irish manuscripts are the oldest to preserve its text.
The T. D. has been used since the time of St. Benedict (Regula, ch. XI) at the end of the nocturnal Office on Sundays and feast days (in Rome, at St. Peter’s in the time of Amalarius, 8th–9th centuries), only on the anniversary days of popes, and on days when the «Gloria» is said at Mass. In the Celtic liturgy the T. D. serves as an eucharistic chant «when priests are communicating»; the same is true in the Gallican liturgy, where it is also found as a song of thanksgiving. In the Roman liturgy it enters as a song of praise, thanksgiving, and triumph (in the consecration of bishops, the blessing of abbots, kings, and queens, and in all the most solemn moments).
Notable variants in the ancient text include: at V. 16, «ad liberandum mundum suscepit hominem» (now «ad liberandum suscepturus hominem») and at V. 21, «gloria numerari» (now «in gloria numerari»).
In its melody, two cadences are distinguished, one after V. 13 and the other after V. 21. The melody of the first part (1–13) seems to be sung in the manner of the Preface, while the second part is in the Gregorian psalm tone IV.