Today, Thursday in the fourth week of Advent, is a greater, non-privileged, ferial day of simple rite. The liturgical colour is violet. Being Advent there is no commemoration of the Vigil in the Office of the Advent ferial day.
At Mattins the invitatory is Prope est jam Dominus: Venite adoremus and the hymn is Verbum supernum prodiens. In the nocturn the antiphons In Deo salutare meum etc from the Psalter for Thursday are sung with the nine psalm divisi (four psalms split into nine sections). The lessons are taken from the thirty-third chapter of Isaias. Three responsories are sung after the lessons and the Te Deum is omitted. At Lauds the antiphons proper to the Thursday before the Vigil of the Nativity, De Sion etc., are sung with the psalms of the second schema of Lauds (Pss. 50, 89, 35, Cantemus Domino & 146). The hymn is En clara vox. The antiphon on the Benedictus is proper to the day, Vigilate etc. After the antiphon is sung in full at the end of the Canticle the choir kneels and the ferial preces are sung. The collect is of the preceding Sunday and the Suffrage is omitted.
At the Hours the antiphons from Lauds are used in the usual sequence. At Prime De Sion etc is sung with psalms 22, 71i, 71ii & 97 (the latter displaced from Lauds by the Miserere). The chapter is the ferial Pacem et veritatem and the versicle in the responsory is Qui venturus es in mundum. The choir kneels to sing both the Dominical and ferial preces. At the other Horae Minores the short set of ferial preces is sung, kneeling, before the collect.
Mass, of the Vigil of St. Thomas, is sung after None. The ministers wear violet dalmatic and tunicle. The Mass Ego autem is sung. The Gloria is not sung. The second collect is of the Advent feria, the third collect is of the BVM in Advent, Deus qui de beate. The Creed is omitted and the common preface is sung. As the Gloria is not sung the dismissal is Benedicamus Domino, sung by the deacon facing the altar.
Vespers are first Vespers of the feast of St. Thomas the Apostle with a colour change to red. The antiphons Hoc est praeceptum meum etc are sung with psalms 109, 110, 111, 112 & 116. The Office hymn is Exsultet orbis gaudiis. The antiphon on the Magnificat is proper to the feast, Quia vidisti me etc. After the collect of the feast the Advent feria is commemorated with the Great 'O' Antiphon appointed for the 20th December O clavis David and the collect of the preceding Sunday. At Compline the Dominical psalms are sung and the preces are omitted.
In the 'liturgical books of 1962' the Vigil of St. Thomas has been abolished. At Lauds the ferial preces are not sung. At Prime the the fourth psalm is omitted, the chapter is the festal Regi saeculorum and the Dominical and ferial preces are omitted. The preces are also omitted at the other Little Hours. Mass, of the Advent feria, is sung after Terce and the ministers wear dalmatic and tunicle, there is only one collect and the dismissal is Ite, missa est. Vespers are ferial and the Great 'O' antiphon is treated like any other throughout the year. There is not even a commemoration of St. Thomas. At Compline the ferial psalms are sung although the Dominical preces are omitted.