The calendar of the church year provides rules of precedence concerning principal feasts, Sundays, holy days, days of special devotion, and days of optional observance (BCP, pp. 15-18).
These rules determine which feast or observance has priority.
The seven principal feasts (Easter Day, Ascension Day, the Day of Pentecost, Trinity Sunday, All Saints’ Day, Christmas Day, and the Epiphany) take precedence over any other day or observance.
In addition to the seven principal feasts, the feasts of the Holy Name, the Presentation, and the Transfiguration also take precedence over the Sunday observance.
Sunday takes precedence over all other feasts and observances of the church year.
When a feast of our Lord or other major feast appointed cannot be observed because it occurs on a Sunday, the feast is normally transferred to the first convenient open day in the following week.
Major feasts falling in Holy Week or Easter Week are transferred to the week following the Second Sunday of Easter, in the order of their occurrence.
When a Feast of our Lord or another major feast occurs on a Sunday but does not take precedence, the collect, preface, and one or more of the lessons appointed for the feast may be substituted for those of the Sunday. However, this substitution may not be done from the Last Sunday after Pentecost through the First Sunday after the Epiphany, nor from the Last Sunday after the Epiphany through Trinity Sunday.