Ranking of liturgical days in the Roman Rite
The Ranking of liturgical days in the Roman Rite is a regulation for the liturgy of the Roman Catholic church. It determines for each liturgical day which observance has priority when liturgical dates and times coincide (or "occur"), which texts are used for the celebration of the Holy Mass and the Liturgy of the hours and which liturgical color is assigned to the day or celebration. Ranks. Each day in the Catholic liturgical calendar has a rank. The five basic ranks for the Ordinary Form of the Roman Rite, in descending order  of importance, are as follows: All holy days of obligation are also solemnities; however, not all solemnities are holy days of obligation. For example, The Nativity of the Lord Jesus (Christmas) (25 December) is a solemnity which is always a holy day of obligation, whereas the Nativity of Saint John the Baptist (24 June) is not a holy day of obligation. In certain locales, certain days which are celebrated as feasts or memorials in most of the Church are celebrated as solemnities; for example, St. Patrick's Day is a solemnity in Ireland, but is normally a memorial for the  rest of the Church; Our Lady of Sorrows is a solemnity in Slovakia, whereas it is a memorial in all other places. History. The ranking of feast days of saints and of Christian mysteries such as the Ascension of the Lord, which had grown from an original division between doubles and simples, developed into a more complicated hierarchy of "Simple", "Semidouble", and "Double", with feast days of the Double Rite further divided into "Double of the I Class", "Double of the II Class", "Greater Double" or "Major Double", and "Double", in order of descending rank. What the original meaning of  the term "double" may have been is not entirely certain. Some think that the greater festivals were thus styled because the antiphons before and after the psalms were "doubled", i.e. twice repeated entire on these days. Others, with more probability, point to the fact that before the ninth century in certain places, for example at Rome, it was customary on the greater feast days to recite two sets of Matins, the one of the feria or week-day, the other of the festival. Hence such days were known as "doubles". The Catholic Encyclopedia of 1907 shows the incremental crowding of  the calendar with the following table based on the official revisions of the Roman Breviary in 1568, 1602, 1631 and 1882, and on the situation in 1907. In 1907, when, in accordance with the rules in force since the time of Pope Pius V, feast days of any form of double, if impeded by "occurrence" (falling on the same day) with a feast day of higher class, were transferred to another day, this classification of feast days was of great practical importance for deciding which feast day to celebrate on any particular day. Pope Pius X simplified matters considerably in  his 1911 reform of the Roman Breviary. In the case of occurrence the lower-ranking feast day could become a commemoration within the celebration of the higher-ranking one. Further retouches were made by Pope Pius XII in 1955, Pope John XXIII in 1960, and Pope Paul VI in 1969. On ferias and many feast days of simple rank, the celebrant was permitted to substitute a Mass of his own choice such as a votive Mass, or a Mass for the dead. Before the reform of Pope Pius X in 1911, ordinary Doubles took precedence over most of the semidouble  Sundays, resulting in many of the Sunday Masses rarely being said. While retaining the semidouble rite for Sundays, the reform permitted only the most important feast days to be celebrated on Sunday, although commemorations were still made until the reform of 1960. The division into doubles (of various kinds), semidoubles, and simples continued until 1955, when Pope Pius XII abolished the rank of semidouble, making all the previous semidoubles simples, and reducing the previous simples to a mere commemoration in the Mass of another feast day or of the feria on which they fell. Then, in 1960, Pope John XXIII  completely ended the ranking of feast days by doubles etc., replacing it by a ranking, applied not only to feast days but to all liturgical days, as I, II, III, and IV class days. The 1969 revision by Pope Paul VI divided feast days into "solemnities", "feasts" and "memorials", corresponding approximately to Pope John XXIII's I, II and III class feast days. Commemorations were abolished both as a rank of liturgical day and as the addition of a second set of Collect, Secret, and Postcommunion for that commemoration after the Collect, Secret, and Postcommunion of the day at Mass.  While some of the memorials are considered obligatory, others are optional, permitting a choice on some days between two or three memorials, or between one or more memorials and the celebration of the feria. On a day to which no obligatory celebration is assigned, the Mass may be of any saint mentioned in the Roman Martyrology for that day. The developments in the ranking of feasts according to the Roman Breviary's calendar can be summarised thus: Sundays. Pope John XXIII's Code of Rubrics divided Sundays into two classes. Sundays of the I class were the four of Advent , the four of Lent, the two of Passiontide, Easter Sunday, the Octave of Easter (in some traditions, called "Low Sunday"), and Pentecost. No feast whatsoever could replace the celebration of these Sundays, with the sole exception of the feast of the Immaculate Conception. All other Sundays were of II class, and outranked feasts of II class, with the exception that feasts of the Lord, whether I or II class, which replaced the celebration of any II class Sunday on which they happened to fall. The 1955 reform of Pope Pius XII did not have this division of Sundays into classes . Instead it laid down that the Sundays of Advent and Lent and those that follow up to Low Sunday, and also Pentecost Sunday, are celebrated as doubles of the first class, and outrank all feasts; but when feasts of the first class occur on the second, third or fourth Sunday of Advent, Masses of the Feast are permitted. Sundays previously celebrated in the semi-double rite were raised to the double rite. A feast of our Lord occurring on a Sunday "per annum" was to take the place of the Sunday. Ferias. In addition to his division of festal days  and Sundays, Pope John XXIII introduced a division of ferias into four classes: Before that, ferias were either "major" or "minor". The major, which must have at least a commemoration, even on the highest feasts, were those of Advent and Lent, the Ember days, and the Monday of Rogation week; the others were called minor. Of the major ferias Ash Wednesday and the days of Holy Week were privileged, so that their office must be taken, no matter what feast might occur. Ember days are four separate sets of three days within the same week—specifically, the Wednesday, Friday, and  Saturday—roughly equidistant in the circuit of the year, that were formerly set aside for fasting and prayer. These days set apart for special prayer and fasting were considered especially suitable for the ordination of clergy. The Ember Days are known in Latin as "quatuor tempora" (the "four seasons"), or "jejunia quatuor temporum" ("fasts of the four seasons"). They occur in the weeks between the third and fourth Sundays of Advent, between the first and second Sundays of Lent, between Pentecost and Trinity Sunday, and beginning the first Wednesday after the Exaltation of the Holy Cross (September 14), which is  between the liturgical third and fourth Sundays of September. Rogation Days are, in the calendar of the Western Church, four days traditionally set apart for solemn processions to invoke God's mercy. They are April 25, the Major Rogation (or Greater Litanies), coinciding with St. Mark's Day (but transferred to the following Tuesday if they fell on Easter); and the three days preceding Ascension Thursday, the Minor Rogations (or Lesser Litanies). These are indicated below in the main body of the calendar and in the Movable Feasts section. Vigils. In early times, every feast had a vigil, but the  increase in the number of feasts and abuses connected with the evening and night service of which the vigils originally consisted, led to their diminishment. Nevertheless, the Roman Rite kept many more vigils than other Latin liturgical rites such as the Ambrosian Rite and the Mozarabic Rite, and if they fell on a Sunday transferred them to the previous Saturday. In the Tridentine Calendar, there were initially seventeen vigils (excluding The Vigil of Easter on Holy Saturday morning), divided into "major vigils" and "minor" or "common vigils". Christmas, the Epiphany and Pentecost comprised the major vigils. The common vigils included  the Ascension of Our Lord, Saint John the Baptist, the Assumption of the Blessed Virgin Mary and All Saints. Most feasts of the Apostles also had vigils, namely Saints Andrew, Thomas, James, Simon and Jude. Whilst the vigils of the Immaculate Conception, Saints Peter and Paul, Saint Lawrence, Saint Bartholomew and Saint Matthew remained, they soon came to be impeded by higher-ranking feasts added to the calendar, and they were instead commemorated as part of other Masses rather than observed in their own right. The Vigil of St. Matthias was unique, in that it was normally commemorated on 23  February, the feast of St. Peter Damian, but in leap years was kept on 24 February, the leap day of the Roman calendar. Pope Pius XII divided Vigils into only two classes: "privileged vigils" (Christmas and Pentecost) and "common vigils" (Ascension of Our Lord, Assumption of the Blessed Virgin Mary, Saint John the Baptist, Saints Peter and Paul, Saint Lawrence). All other vigils, even those in local calendars, were suppressed. The vigils of Saints Peter and Paul and Saint Lawrence, however, continued to be impeded by higher-ranking feasts. In Pope John XXIII's 1960 Code of Rubrics, Vigils were  divided into three classes. The Easter Vigil was left out of the calculations, being celebrated in a different way from that of other Vigils. The Vigils of Christmas and Pentecost were of the I class, and took precedence over any feast. The II class Vigils were those of the Ascension of Our Lord, the Assumption of the Blessed Virgin Mary, Saint John the Baptist, and Saints Peter and Paul; they took precedence over liturgical days of III or IV class. There was only one III class Vigil, that of Saint Lawrence, which had precedence only over IV class liturgical days . Octaves. The Tridentine Calendar had many octaves, without any indication in the calendar itself of distinction of rank between them, apart from the fact that the Octave Day (the final day of the octave) was ranked higher than the days within the octave. Several octaves overlapped, so that, for instance, on 29 December the prayer of the saint of the day, Saint Thomas Becket, was followed by the prayers of Christmas Day, of Saint Stephen, of Saint John the Evangelist and of the Holy Innocents. The situation remained such until the reform of Pope Pius X. To cut down on  the monotony of repeating the same prayers in Mass and Office every day for eight days, Pope Pius X classified the octaves as "privileged", "common" or "simple" The privileged octaves were of three "ranks". The first rank belonged to Easter and Pentecost (permitting no feast to be celebrated during them, or even to be commemorated until Tuesday Vespers), the second to Epiphany and the Solemnity of the Most Holy Body and Blood of Christ (the Octave Day ranked as a Greater Double, the days within the octave as semidoubles, giving way only to Doubles of the I Class, and on  the Octave day itself only to a Double of the I class which was celebrated in the entire Church), the third rank to Christmas, the Ascension, and the Sacred Heart (these gave way to any feast above the level of Simple). The common octaves were those of the Immaculate Conception, the Assumption, the Nativity of Saint John the Baptist, the Solemnity of St. Joseph, Saints Peter and Paul, and All Saints, as well as, locally, the principal patron saint of a church, cathedral, order, town, diocese, province, or nation. These too gave way to any feast above the level of  Simple. The difference between them and privileged octaves of third rank concerned which Psalms were said in the Divine Office. The simple octaves were those of Saint Stephen, Saint John the Evangelist, the Holy Innocents, Saint Lawrence, the Nativity of Mary and, locally, secondary patrons. These were all Doubles of the II class, their Octave day was a Simple and, in contrast to the situation before Pope Pius X, their Mass was not repeated on the days within the octave. In Pope Pius XII's reform, only the octaves of Christmas, Easter and Pentecost were kept. The days within the  Easter and Pentecost octaves were raised to double rite, had precedence over all feasts, and did not admit commemorations.