Occurrence and Concurrence of Liturgical Celebrations is the calendrical distinction between celebrations assigned to the same civil day and celebrations whose liturgical times meet at Evening Prayer or another boundary between days.
Occurrence: two claims on one date
Occurrence happens when two liturgical celebrations fall on the same calendar day. The Table of Liturgical Days determines precedence. Depending on rank and specific norms, the lower celebration may be omitted, transferred, celebrated elsewhere under a proper calendar, or reduced to an optional commemoration; it is not automatically moved to the next open weekday.[1]
Occurrence can affect Mass and the Liturgy of the Hours because both follow the liturgical day, but each book's rubrics still govern its texts. A saint printed on a civil calendar has not necessarily been liturgically celebrated when a Sunday or higher observance occurs. The Liturgical Ordo records the lawful result for a particular place and year.[2]
Transfer
Certain impeded solemnities are transferred according to universal or particular norms; most memorials are simply omitted when a higher day prevails. Transfer is a juridical calendar act, not an informal decision to celebrate a displaced feast whenever attendance will be larger.
Omission and optional commemoration
Omission means that the lower observance is not celebrated in that calendar that year. On specified privileged weekdays, an optional memorial may instead be commemorated in a reduced manner. Neither outcome denies the saint's holiness or removes the name from the Roman Martyrology.[3]
Concurrence: celebrations meet at a boundary
Concurrence occurs when First Evening Prayer of the following celebration meets Evening Prayer of the current day. It therefore concerns liturgical time at the transition between dates rather than two entries printed in the same date box. The higher-ranking celebration prevails according to the table and the specific norms for Sundays and solemnities.
Not every feast or memorial has First Evening Prayer. Solemnities ordinarily do, and Sundays begin with First Evening Prayer, while other ranks follow their books. Assuming every liturgical observance begins the prior evening confuses a proper vigil or first vespers with the general civil custom of anticipating events.
Mass, Office, and days of precept
The Office's concurrence rules do not by themselves choose every evening Mass formulary. A Mass celebrated on the preceding evening can satisfy a Sunday or holy-day obligation under canon 1248, yet the proper Mass is determined by liturgical law, calendar precedence, pastoral scheduling, and any proper Vigil Mass. Obligation and formulary are related but non-identical questions.
Careful terminology prevents a common cascade of errors. Occurrence does not mean concurrence; First Evening Prayer does not automatically create a Vigil Mass; transfer does not create an External Solemnity; and an anticipated obligation Mass does not move the liturgical date. Each classification controls one part of the calendar decision.
References
- 1.Universal Norms on the Liturgical Year and the General Roman Calendar — The universal Roman norms for rank, precedence, proper celebrations, occurrence, concurrence, omission, and transfer
- 2.General Instruction of the Liturgy of the Hours — The official general instruction governing the Hours, including the extended vigil form of the Office of Readings
- 3.General Instruction of the Roman Missal — The authoritative structure and rubrics of Mass, including memorial commemorations and Masses chosen for serious needs