A priest can celebrate Mass sin populo, i.e. without a congregation. The rubrics for this are in the General Instruction on the Roman Missal (GIRM), which is readily found online. If I remember correctly there must be a single server present; I don’t think a priest can completely celebrate alone unless the absence of a minister prevented him saying Mass. Is there any reason why you asked about St. Peter’s in particular. A priest can celebrate Mass sin populo anywhere that Mass may be celebrated.If a priest wanted to say a private OF Mass in say ST Peter’s Basillica on one of the side altars alone without a minister, what would be the rubric differences compared to a public Mass? How would such a Mass go?
Can it be done?
From the 2002 General Instruction of the Roman Missal (GIRM) approved for the USA, which can be accessed from romanrite.com/girm.html :If a priest wanted to say a private OF Mass in say ST Peter’s Basillica on one of the side altars alone without a minister, what would be the rubric differences compared to a public Mass? How would such a Mass go?
Can it be done?
What would be a just and reasonable causeFrom the 2002 General Instruction of the Roman Missal (GIRM) approved for the USA, which can be accessed from romanrite.com/girm.html :
“III. MASS AT WHICH ONLY ONE MINISTER PARTICIPATES
252. At a Mass celebrated by a priest with only one minister to assist him and to make the responses, the rite of Mass with a congregation is followed (cf. above, nos. 120-169) the minister saying the people’s parts as appropriate.
253. If, however, the minister is a deacon, he performs his proper duties (cf. above, nos. 171- 186) and likewise carries out the other parts, that is, those of the people.
254. Mass should not be celebrated without a minister or at least one of the faithful, except for a just and reasonable cause. In this case, the greetings, the introductory or explanatory remarks (monitiones), and the blessing at the end of Mass are omitted. …”
The description of this Mass continues through to paragraph 272.
A wide variety of things would be just and reasonable. In general, unless a law is penal, the Church says we are to interpret laws widely. I believe, but could, of course, be wrong, that Bl. John Paul II said that the desire of a priest to celebrate Mass was a just and reasonable cause.What would be a just and reasonable cause
Should he say the Canon loudly or whisper?It would be the same at St. Peter’s as it would be at any other church, although making arrangements to actually do this would be rather complicated.
As to the Mass itself, it happens just like any other Mass except for the obvious fact that the priest would be doing everything. So the priest would read the first reading and psalm rather than a lay reader (although a lay reader isn’t required even in a Mass with a congregation). I mention that only in case people were wonderring is some parts would be omitted.
Some parts are indeed omitted, but only the “obvious” parts. So, in the beginning, the priest would not say “Brethren, to prepare ourselves…” instead, he simply begins the Confiteor without introducing it. All of the "The Lord be with you"s are omitted–except for the one at the beginning of the Preface.
Same thing with the Our Father. The priest doesn’t say “Let us pray with confidence to the Father…” because there’s no one to whom those words are addressed. Instead, he just begins the Our Father after the Amen from the end of the Canon.
In other words, the words that are specifically addressed to the congregation are omitted. All the prayers are retained.
Finally, there’s no blessing at the end. Instead, the priest simply ends by making the sign of the cross over himself (no, this isn’t in the rubrics as such, but it does seem necessary)
Personally, here’s how I do the psalm. I read the response-verse, then the entire psalm, then end with the response-verse. In other words, no psalm-verse-psalm-verse. This is one of the options for any day, although it’s not often used.
Rather than go through every single part of the Mass and describe it (which would make for a long post, and I’d likely miss something). Is there any particular part of the Mass that you’d like to know about?
Finally, because this will probably come up, the priest must say the Mass, not just think it. So while volume isn’t necessary (he doesn’t have to worry if the people in the back can hear him), he does have to make sound come out of his mouth, and must be moving his lips so that he’s actually speaking and not just thinking them.
This is something that is hard to define but rather to give practical examples.What would be a just and reasonable cause
It doesn’t matter. The point is that he must actually say it. The volume is irrelevant.Should he say the Canon loudly or whisper?