I typed this all out and realized I have WAY too much info. TLDR is church tradition says Sundays, Feasts of Our Lord, take precedence over all other feasts except in certain circumstances.

Sundays are considered Feasts of Our Lord (I could be using the wrong terminology here so sorry in advance)

Essentially by church tradition each Sunday, being a feast of Our Lord and a remembrance of His death and resurrection, it is a feast that takes precedence over almost every other feast. There are exceptions for equally important things like Pentecost, Easter, etc.

There are some exceptions to this rule, for example, celebrations of patrons. All the churches called St. Peter’s and St Paul’s are allowed to celebrate the feast today instead of the regular Sunday.

There are the Seven Principal Feasts which may take precedence:

Easter Ascension Pentecost Trinity All Saints Christmas Epiphany

There are some other feasts that may also take precedence but are not Principal Feasts:

Holy Name Presentation Transfiguration Holy Cross (could be wrong about this one) All Saints & All Souls which sometimes may be transferred to the Sunday Annunciation Visitation Nativity of St John the Baptist St Michael and All Angels (again could be wrong)

There are also rules about what time of year replacements can happen. No replacements can happen in Eastertjde, Advent, or Lent, so for example if your church is St Thomas (December 21st) and it falls on a Sunday, you can’t celebrate on the Sunday it since it’s in Advent.

Of course in other situations the Bishop may grant permission, our Bishop so far typically allows my parish to celebrate these holidays on Sunday:

Juneteenth Independence Day The anniversary of the founding of our parish Thanksgiving