If you go to the Mass this afternoon or evening at your parish, what readings, prayers, topics and music will you hear?
Will it be:
Mass for the Solemnity of the Assumption of the Blessed Virgin Mary?
Or will it be an anticipatory Mass for Sunday?
In Piqua, it will be the Mass of the Assumption. Why?
Well, the Church assigns different solemnities and feasts different ranks. And there is no question that the Solemnity of the Assumption is a higher rank than the Solemnity of the 20th Sunday in Ordinary Time. Ergo, the Assumption--in my reading of the rubrics--takes precedence all day today. Tomorrow, however, is Sunday, and that's when the prayers for the 20th Sunday in Ordinary Time kick in.
Why is there any question?
Well, almost all pastors, and those who assist them, rely on a booklet called the "Ordo," which is designed to gather in one place all the various bits of information one needs all year long about such things. Liturgical books don't always have the newest saints and blesseds added to the church's calendar, for example. The Ordo is very handy in that regard.
However, it was ambiguous regarding this question--it simply didn't say explicitly what I said. Nor did it say the opposite. If you read it closely, however, it says that Second Vespers (i.e., Evening Prayer II) for tonight is for the Assumption, not for Sunday, as it otherwise would be. That confirms what I said.
If pastors don't all do what I'm describing, why wouldn't they?
Well, this happens infrequently, and one tends to forget how it was the last time, say five or six years prior. Also, it will be confusing for readers and musicians, so it is easier to treat the Saturday evening and Sunday Masses the same. Also, the bishops caused some confusion when they created the rule that sometimes a holy day of obligation is not obligatory. I.e., Assumption isn't obligatory when it falls on Saturday or Monday--the rationale being that it's taxing if there are too few priests as there are in many places. I wish the bishops had decided that otherwise. To the minds of many, including, I think, many priests, "not an obligatory holy day" equals saying it's not a solemnity of the highest rank; but this is simply not so.
What about the Sunday obligation?
In my judgment, the Sunday obligation is fulfilled when one goes to the Saturday evening Mass, whether it's for Assumption or anticipatory for the next day. This is the case every time an obligatory day falls on a Saturday--if Christmas falls on Saturday, and Saturday evening Mass must be for Christmas, but it "counts" for either Christmas (that day) or for Sunday, the next day. No double-dipping.
If there are two obligatory days back-to-back, one is obliged to take part in divine worship twice at Mass, sometime between the vigil of the prior obligatory day, through the evening of the second obligatory day--i.e., over three calendar days. Since Assumption isn't an obligatory day, then there's no difficulty about "applying" it to Sunday.
I realize some will say, why isn't it simpler?
First, because when you have any sort of law that obliges people, you have to spell out the details so people know how the law applies.
Second, some of the complexity comes in providing exceptions and accommodations, which is because all these things really are for the benefit of the human beings involved--so accommodating people's weaknesses or work schedules and so forth is a good thing to do, to whatever degree seems reasonable.
Some will say, the Church shouldn't have "laws," but come on--do you have "laws" (you likely call them "rules") in your home? Your workplace? In organizations? Does our society operate without laws? So why expect the society and family we call the Church not to have need for laws and rules, when every other aspect of family and society requires them for good order?
Besides, God has laws--and while the Church does not equal God, the Church is an extension of God, acting with his authority. The Church is a unique entity, being both human and divine at one time; it is the Body of the perfect, sinless, Divine and incarnate Son, filled with the Holy Spirit--and yet its members are sinful human beings. A mystery, St. Paul says in his letter to the Ephesians! When the Law of God is written perfectly in our hearts we will have no need of any other law--i.e., the Beatific Vision! Until then, we need more helps.