Aware of the dangers of offering an opinion on canonical or liturgical matters in, of all things, a blog format, I venture to post the following.
What follows is merely my personal opinion, not an official statement of the Catholic Church or of my Archdiocese -- so please consider this as just my own "thinking out loud" as a canon lawyer, and one who knows that she is in the minority opinion on this matter:
There's a lengthy debate over on the canon law listserve/discussion group I belong to among the canonists, many of whom insist that the faithful must attend, specifically, a Mass which celebrates the Immaculate Conception, and then also the Mass of the Second Sunday of Advent. I don't understand why a Catholic would not want to celebrate both, but this is not about what is laudable but rather what the possibilities might be for those who normally can attend, or only want to attend, only one Mass next weekend.
I have been wondering if the principle of "favors are to be generously interpreted, and burdens restricted" might apply to this situation, as I will describe below (in the underlined section with bold lettering). The "burden" in this case is the obligation to attend Mass; next weekend it would appear that there are two "burdens" on successive days. The "favor" which may be possible due to this situation -- to "combine" obligations -- is the result of the circumstances which arise from the "collision" of canon law and liturgical law.
However, PLEASE consult your own pastor at your local parish about this.
For starters, here's a look at the law:
Canon 1247: On Sundays and other holy days of obligation the faithful are bound to participate in the Mass; they are also to abstain from those labors and business concerns which impede the worship to be rendered to God, the joy which is proper to the Lord's Day, or the proper relaxation of mind and body.
Canon 1248.1: The precept of participating in the Mass is satisfied by assistance at a Mass which is celebrated anywhere in a Catholic rite either on the holy day or on the evening of the preceding day.
The faithful must participate in the Mass on Sundays ("and other holy days of obligation"), either on the Sunday or Holy Day "or on the evening of the preceding day" ("vel vespere diei praecedentis"), regardless of the Mass texts -- the liturgical calendar and Sunday Mass texts are often different in the Eastern liturgies and in the Classical Roman Rite or "extraordinary form," as well as in the other liturgical rites or uses of the Latin Church; the Ambrosian, the Rite of Braga, the Dominican Rite, the Anglican Use, etc. Also, one may be visiting or living in a place where one does not know the language, and yet may still fulfill the Sunday or Holy Day obligation just by attending Mass at a local Catholic church even if one does not understand a word of it.
A Catholic may attend any Catholic rite, viz., any Eucharistic liturgy of any Catholic Church (Latin Catholic or Eastern Catholic -- e.g., Byzantine, Maronite, Melkite, Chaldean, Syro-Malabar, etc.). Since Sunday vigil Masses (Sunday Mass on Saturday, using Sunday Mass texts) do not exist in most of the Eastern Catholic Churches sui iuris (though they seem to be happening more and more in the U.S., much to the regret of some) nor in the Latin usus antiquior (with a few exceptions), if one attends Mass or Divine Liturgy on a Saturday afternoon or evening, no matter what readings are read or which propers and collects are used, etc., one fulfills the Sunday Mass obligation. The faithful cannot be required to "hear" only one particular set of readings and propers, nor can they be required to hear them in any particular language. For Byzantine Catholics (and most of the Orthodox), the feast day of Our Lady's conception (The Conception of the Most Holy Mother of God by the Righteous Anna or the Maternity of Holy Anna or the Conception of the Theotokos) is commemorated on December 9th (though apparently in some years it actually is on December 8th).
Could anyone argue that I had not thereby also fulfilled my Sunday Mass obligation as well? I have attended Mass on the vigil or eve of Sunday, "on the evening of the preceding day" -- even though the texts of the Mass were not those of the Sunday, but rather still those of the Immaculate Conception.
I realize that it is extremely important to keep the Sunday from being a completely non-liturgical or a-liturgical day for the faithful, and that Catholics *should* want to keep Sunday as a great liturgical celebration, and for the upcoming weekend of December 8-9, to attend both the Holy Day AND the Sunday, but this is not about what is desirable, but rather what fulfills an obligation to attend Mass. As for Sunday Mass on Saturdays, what's done is done: considerable numbers of the (mostly Latin Church) faithful routinely "take advantage" of the Sunday vigil Mass on Saturday, since they sometimes want their Sundays "free" for other things. This is an unforeseen consequence of some of the well-intentioned liturgical and sacramental changes that began long before Vatican II, in this case allowing evening Masses and Sunday vigil Masses routinely, which was made possible, for the most part, only by the relaxation of the Eucharistic fast (formerly from midnight, reduced to 3 hours before receiving Holy Communion, and one hour in some cases, as decreed in Pius XII's 1953 Apostolic Constitution "Christus Dominus").
I know there is a debate about the time on a Saturday when the Sunday vigil Mass may be celebrated -- some people say 4:00 p.m. or 5:00 p.m.or even 6:00 p.m. (no earlier than 4:00 p.m. is mentioned in the 1953 "Christus Dominus"). But once one has cleared the midday point, one is already "post meridiem" ("p.m."), and one cannot necessarily be "more" p.m. or "less" p.m. -- solar noon has been marked, and now it is "after noon," or rather the "eve" of the next day, even if it is not yet getting dark. Of course, a "day" in canon law is reckoned as a full 24-hour midnight-to-midnight period of time (canon 202).
Waiting until it the day looks or feels like "evening," or waiting until it is getting dark, or until actual sundown, is also not useful as a marker, since, for example, in the very northernmost (and, alternately, southernmost) parts of the world sunset can occur very early in winter and very late in summer.
By 4:00 p.m., it is already dark in Oslo this time of year, and summer in Anchorage means it's light till 11:00 p.m. Also, in Italy, by way of another example, it is an ironclad rule that evening begins at 2:00 p.m. all year round: if one says "buongiorno" instead of "buona sera" after 2:00 p.m., one will be politely but firmly corrected. "Sera" -- evening -- is at 2:00 p.m. In five years in Italy, I only ever heard the rarely-used "buon pomeriggio" on mid-afternoon TV news broadcasts.
Personally, I have encountered a few Carmelite monasteries of nuns in various places in the world where they celebrate Vespers at 2:00 or 2:30 p.m.
And recently, on September 22nd, which was a Saturday, while joining some of my friends for a 2:30 p.m. Mass who were on the Diocese of Wheeling-Charleston's diocesan pilgrimage to the Basilica of the National Shrine of the Immaculate Conception in Washington, D.C., Bishop Bransfield announced that after conferring with Cardinal Wuerl,the participants at the Mass were thereby fulfilling their Sunday obligation. There were audible expressions of surprise among the pilgrims.
I've been to at least one Sunday Mass at a nursing home...at 12:15 p.m. on a Saturday.
Also, consider the more expansive parameters of "evening"and/or "vigil" by recalling that the Easter Vigil used to be held very early on Holy Saturday morning, and that Christmas Eve is the whole day of December 24th.
So, as regrettable as the minimalist mentality might be among some of the faithful, here's the bottom line as far as I'm concerned:
Favorabilia sunt amplianda, odiosa restringenda -- basically, the sometimes-difficult-to-parse canon 18, which is the law undergirding the principle: favors are to be broadly interpreted ("increased"), and hardships/burdens restricted (or strictly interpreted).
I think this is a case of a "favor" that happens to occur every once in a while: the Solemnity of the Immaculate Conception ends liturgically at some point in the late afternoon next Saturday, but it is still the day of December 8th, and if I am at the 6:00 p.m. Mass on December 8th, then I am attending a Mass on December 8th, even if the texts of the Mass are those of the Sunday. If once every few years the faithful can "get away with" attending an afternoon/evening Mass on Saturday, December 8th...well, it's still Saturday, December 8th, no matter which liturgy is being celebrated (again, the faithful can't be forced to hear one particular set of Mass propers or readings in order to fulfill an obligation to attend Mass). And, of course, since one is attending a "Sunday Vigil" Mass, I don't think it is possible to say that one is NOT fulfilling the Sunday obligation.
To close with a personal note:
In terms of catechesis, and pastoral care of the faithful, or just plain concern for the souls of others, I would like to see a greater emphasis on the meaning of the Sunday obligation and its fulfillment -- the meaning of the Sunday, first of all, as well as the obligation to attend, that, barring grave illness, or the need to care for someone who can never be left alone, or sheer moral or physical impossibility, or other serious circumstances (hazardous weather conditions or a car that won't start and the parish is ten miles away), Sunday (or Holy Day) Mass cannot be missed, on pain of serious sin (formerly known as "mortal" sin). Also, another matter that should be addressed is that some people think that if they arrive at Mass before the Gospel, the offertory, the consecration, the Our Father, or some other point, that it still "counts"; or that they are required to receive Holy Communion (and then are free to leave); or other such misunderstandings. Then there are the "absentees": think of the large numbers turning up for Ash Wednesday...not a Holy Day of Obligation. Or the many new faces one sees at Christmas and Easter...and then not the rest of the year. On those three days alone, our pastors have a precious opportunity which should not be wasted. They alone have the pulpit: they must instruct those who rarely come to Mass. Sermons on repentance, or on hope, or on unending joy which are usually associated with these solemn and holy celebrations are very beautiful: but what good is it to give a blind person a beautiful gift and then let him walk out the door onto a ten-lane freeway? Pastors, please seize the moment!