I. Concerning the three Rites by which the Office is said
Before beginning the Office of the day, it is necessary to know by what rite it is to be said; for there are three methods of saying Office, known repectively as the simple rite, the semi-double rite, and the double rite.
When the Liturgy was in an early stage of development, the Office of Saint’s Days was said in addition to the ordinary simple daily Office. On Sundays there was added to the daily Office something in commemoration of the Lord’s Day, and its Office was thus in a sense a semi-double. Gradually these customs developed into a three-fold method (i.e., the three rites by which the Divine Office is now celebrated.
The day was reckoned from sunset to sunset, and hence a Feast could have both I and II Vespers; when Compline was added both Vespers had Compline; when Feasts have both Vespers with Compline following, Vespers may be said to be doubled.
The melody of the Antiphon deteremines the tone of the accompnaying Psalm or Canticle, and hence enough of the Antiphon must be sung to get into the mode of the tone. For the most part only the opening phrase of the Antiphon is used for this purpose, but when the Antiphon is recited in its entirety before as well as after the Psalm or Canticle, the Antiphon is said to be doubled.
Matins is of one Nocturn or three; when it is celebrated with three Nocturns, the Nocturn may be said to be tripled.
On ordinary occasions the Office is given something of a penitential character by inserting petitions called Preces, which are of two sorts, dominical and ferial. The former are said standing, and used only at Prime and Compline; the latter are said kneeling at all the hours except Matins, and are used only in the Office of greater Ferias.
Every day in the year is a commemoration of redemption, whence comes the victory of the Saints, and therefore a memorial of the Saints or of the Cross, called the Common Commemoration, is given for use at Lauds and Vespers except during Advent and Passiontide which are seasons wherein the Redeemer himself is the subject of the Office. (See page A6 in Common Forms).
Bearing in mind the foregoing explanation, the following formula should be clear: (a) on Doubles, Vespers and the Antiphons of the Greater Hours are doubled, the Nocturns tripled, the Preces and Common Commemoration omitted; on Semidoubles (a mixture of the double and simple rite), Vespers is doubled but not the Antiphons, the Nocturns are tripled, and the dominical Preces and Common Commemoration are said; on Simples (the opposite of Doubles), Vespers and the Antiphons are not doubled, nor is the Nocturn tripled, but the Preces and Common Commemoration are saod. (For the Preces see pages A24, 29, 35, 37, 40, 43 and 46 in the Ordinary.)
The Office of some Feasts and most Ferias, and also the Saturday Office of our Lady, is of simple rite. The Office of simple Feasts begins with I Vespers but ends with None on the following day, and the dominical Preces are used at Compline and Prime. But the ferial Office begins where the Office of a Feast terminates, and extends to the point where the Office of another Feast begins, and hance cannot have I Vespers, but merely Vespers of the week-day; Ferias are therefore reckoned from midnight to midnight unless some part of the period be given over to Feast. (The rules for the recitation of the ferial Office are given below in Rubric VII.)
In the foregoing paragraphs nothing is said of the effect of Occurences and Concurrences, and their consequent Commemorations, in modifying the rite of the Office, for these matters are discussed below Rubrics VIII, IX, and X but it is pertinent to remark here on how, in certain cases, there is extended to an Office of semidouble or simple rite the privilige of omitting the Preces and Common Commemoration which was mentioned above as a privilige of the double rite. First as to Octaves (although they are ranked only as Semidoubles), and also the simple Octave Days, continue to have the privilige of their respective Feasts in the matter of excluding the Preces and the Common Commemoration. Often a Semidouble or Double must cede its Office to an Office of the same or of lower rite but of greater liturgical dignity, and is therefore reduced to a Commemoration, in which case the Semidouble or Double is said to be simplified, because in respect of rank it is treated as a Simple; and whenever a simplified Double, or a day within an Octave, or even a simple Octave Day, is commeorated in the semidouble Office (e.g., of Sunday), it likewise excludes the Preces and Cmmon Commemoration, and even the Athanasian Creed at Prime if that were otherwise to have been said. However, whena simplified Double is commemorated in the Office of a simple rite of greater Feria, it excludes only the Common Commemoration (i.e., in this case the Suffrage of the Saints), if that were otherwise to have been said, for the ferial Preces must be said as the mark of a greater Feria.
It was said above that the Nocturn is tripled in the Offices of double or semidouble rite; but an exception should be noted: in the Easter and Whitsun Octaves, the Office is of one Nocturn, and therefore of three Lessons only; and below in Rubric XII there are also given two rules whereby Matins can be simplified, i.e., reduced from nine Lessons to three on certain occasions.
Both Ferias and Feasts are ranked from the rite of their Office, but there are so many Offices of double rite that it is necessary to arrange them in an order of precedence, thus: lesser, greater, II Class and I Class Doubles. The Offices of all I and II Class Doubles are celebrated as excepted or partially excepted. Nevertheless, the general rules of the rite are the same on all Doubles, no matter of what rank they are.