Monday in the fourth week of Advent is a greater, non-privileged, ferial day of simple rite. The liturgical colour is violet.
At Mattins the invitatory is Prope est jam Dominus: Venite adoremus and the hymn is Verbum supernum prodiens. In the nocturn the antiphons Dominus Defensor etc from the Psalter for Monday are sung with psalms 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36 & 37. The twelve psalms are sung in pairs under six antiphons. The lessons are taken from the forty-first chapter of Isaias. These are significantly longer than those found in the Clementine, and later, editions of the Breviary. The first lesson contains the text of the both the modern first and second lessons, the second lesson contains all of the text of the lesson found in modern editions and the addition of Egeni et pauperes ... inviam in rivos aquarum, vv. 17-18. The third lesson, vv. 25-29, is entirely absent from the post-Clementine editions. Three responsories are sung after the lessons and the Te Deum is omitted.
At Lauds the antiphons proper to the Monday before the Vigil of the Nativity, Ecce veniet etc., are sung with the psalms of Monday (Pss. 50, 5, 62-66, Confitebor tibi & 148-149-150). The hymn is Vox clara ecce intonat. The antiphon on the Benedictus is proper to the day, Dicit Dominus etc. After the antiphon is sung in full at the end of the Canticle the choir kneels and the ferial preces are sung. The preces include the psalm De profundis. The collect is of the preceding Sunday and the Suffrage is omitted. No commemoration of the Vigil of St. Thomas is made in the Office. After Benedicamus Domino Mattins and Lauds of the Dead are sung. At Mattins the nocturn has three psalms (5, 6 & 7) followed by three lessons and their responsories. At Lauds psalms 50, 64, 62-66, Ego Dixi & 148-149-150 are sung.
At the Hours the antiphons from Lauds are used in the usual sequence. At Prime Ecce veniet etc is sung with psalms 53, 23, 118i & 118ii. 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 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 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 caelum laudibus. 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 preces are omitted.