It is customary. De Musica sacra does not prohibit it if you follow strict Pius XII/1962 rubrics. I much prefer organ, or silence when solo organ isn’t allowed, to the Marian antiphon, as the celebrant and ministers cannot pray that and the Gospel at once. I will check when I get home to see if Stercky says anything. But it is most certainly allowed.

Yeah it’s not well-known in the US, but outside of it, silence during the Last Gospel (including the Marian antiphon, which I dislike, as I said) is far from the norm.

We didn’t have organ today, and it is a very bad habit to read the Last Gospel out loud, which comes out without the organ there.

And here we are, yet again... No actual authoritative sources addressing the specific point!

The scan of Fortescue's instructions for his organist is not authoritative either, having no proper references for its instructions.

I can see contextually how it might be appropriate to play the organ during the Last Gospel on the basis that a bishop celebrating Pontifical Mass is permitted to recite it privately in procession, rather than at the altar - but was hoping for something stronger than this as an authority in either direction.

begin playing softly after "ET VERBUM CARO FACTUM EST,

Perhaps ubi lex non distinguit, nec nos distinguere debemus applies?

I'm open to being proven wrong in liturgical law, but as far as I know there is not any authoritative source (as observed by the OP). Therefore, I say it can be decided at the parish level unless a higher authority passes down a ruling. I personally prefer organ during the Last Gospel at a Sung Mass, and like to improvise building up to the Marian antiphon or other hymn/piece for the final procession.

I have also worked under pastors who forbade the practice, but without any citation of liturgical law.

My practice has been this:
During Advent and Lent the celebrant reads the Last Gospel silently and raises his voice at the words “ET VERBUM CARO FACTUM EST” alone.
After the conclusion, he comes to the foot of the altar and intones the Marian Antiphon.

In Eastertide, I play a little ditty overtop of the Last Gospel, then the celebrant comes to the foot of the altar where he intones the Regina Cæli.

For the rest of the year I simply begin my postlude after the blessing, which seems to solemnize the action whilst the servers take their places for the exit.

Only in Low Masses is the Last Gospel read aloud, where I am.

i play all the time during last gospel, softly, usally improv based loosely on the Ite

And we’re back to customs yet again! I’m not sure that there is complete silence on this point, MatthewRoth. It is possible there are sources that have not been explored yet - including the published decisions of the relevant congregation. Those are the kinds of sources I’m asking about here.

I expect also that Fortescue based his advice on something other than a whim - and that being done with ‘Ceremonies’, did not want to create anything resembling it ever again!

If Stercky does not condemn the practice with a reference to the Roman authorities, then it probably was never taken up by them, because he does so in many cases where it is clear that he is condemning an abuse known to him and the authors who initiated the volumes of which he was the final editor. But in fact, he doesn’t mention it at all, even though wall-to-wall music, the way that I was taught as essential and really something that I came to love while learning under Nick Botkins at SFDS years ago now, is characteristically French, suggesting that it really is about custom…

I understand and have from the beginning what you’re after, and I’m afraid that you need to go look in AAS yourself. Which is not an easy task.

There are decrees stating that it is not permissible to begin the singing of a canonical hour or the absolution at the catafalque (pre-1960 rubrics) during the Last Gospel. Terry says that the organ is played during the Last Gospel (whenever organ playing is permitted) and that at Sunday Mass in England the Domine salvum fac regem is sung during the Last Gospel. I don't think you'll find an S.R.C. dubium response regarding what was a widespread practice, because who would have asked such a thing?

The index and Ctrl-F of the Decrees of the Sacred Congregation of Rites (from the years 1588 to 1911) yielded no obviously relevant results.

Searchable PDFs of a compilation of the Decrees are available at https://www.restorethe54.com/resources/ (about halfway down, under "Legal Resources").

because of the added music the rules of the LG said loud at the read mass don’t apply

Is there some authority for this other than local custom?

That is in the High Mass section, which is a bit odd, because the Last Gospel is read silently at High Mass according to general rubric 513e, and aloud at Low Mass according to 511j. It's not a matter of the priest taking his pick.

FSSPMusic - Which general rubric applies to Missa Cantata?

Thanks - By observing what is said in the preceding section (presumably 513), we seemingly have the basis for a silent recitation of the Last Gospel at Missa Cantata.

A deeper dive into Terry is proving most interesting. Thanks again FSSPMusic for the gift that keeps on giving!

Specifically, Terry cites Gavantus at one point. I took a look at Gavantus to see whether there was any specific mention of the Last Gospel and what the organist should (or shouldn't!) do. Nothing so far. What IS there, which I think does shed more light on the situation is the range of circumstances in which the Last Gospel was replaced with the Gospel of the Sunday (etc) because the Mass of the Sunday had in turn been displaced by another Mass. Pius X happily restored the preeminence of the Sunday, so most of this kind of rubrical wrangling has been out of existence for more than 100 years now.

Historically, it seems a situation emerged in which the Last Gospel would not have been said silently after all Solemn Masses. Against this backdrop, some ambiguity as to whether or not the organ was to be played makes perfect sense.

I'm curious why you would think a proper Last Gospel would be read aloud at Solemn High Mass even though the ordinary one would not. I checked the 1920 edition of Fortescue, which says that the final blessing said aloud "is the only case of words spoken (not sung) in this manner at High Mass." The 1943 edition says the following:

If there is a last Gospel special to the day, the celebrant should wait before giving the blessing, that the subdeacon may have time to carry the Missal across. He turns to give the blessing [footnote: He should wait till the sung response, “Deo gratias,” is finished. He says the formula of blessing just as at Low Mass, that is loud enough to be heard by all (R. XII, 1, 7).] and says the last Gospel in a low tone.

And the 2009 edition:

If there is a last Gospel proper to the day, the celebrant should wait before giving the blessing, so that the subdeacon may have time to carry the missal across. He turns to give the blessing [footnote: He should wait till the sung response, Deo gratias, is finished. He says the formula of blessing just as at low Mass, that is to say, loud enough to be heard by all (R., XII, 1, 7).] and says the last Gospel silently.

That is not to say that a silent recitation of a proper Last Gospel did not occur in places, only that on points such as this, there is a greater likelihood of disparity.

I am not making an argument for what is or isn't rubrically correct at this point - only the ways in which local usage (guided or misguided) may have coloured performance practice, and why there is some lingering doubt on this issue.