My own experience on organ accompaniment is that it drives out subtlety in singing the chant. And not just to an insignificant degree.

We held many E.F. liturgical conferences in the 1990s in which we sang several hours of the Office. The little hours were invariably unaccompanied. It was at those hours that IMO the psalmody was best sung. By that I mean that the wave (arsis/thesis) of a psalm verse and half verse was learnt and applied at those times. (We had short workshops before each hour to teach the melodies and dynamics.)

To me, (it was remarkable at first) it was a constant joy that an untrained congregation could pick up and apply the dynamic so well. Why was this? I think the answer is quite simple: not having an organ covering all, everyone could hear the mistakes in volume or length, and by your own lights, or if need be a sharp but charitable jab in the rib from you neighbor, you'd be goaded back to the right path. If the organ is playing, so that the nuances or lack thereof are difficult to discern, the more sensitive singers just give up. The wave is largely drowned out by the sound of the organ: it swamps those observing it, and those not doing so can't hear that they're out of whack. To put it another way: one can distinctly hear when a group is singing together in volume and rhythm (let alone pitch) when it's unaccompanied, as opposed to when it is accompanied.

I hasten to add that our organists at the greater offices were excellent and sensitive accompanists, who were aware of these nuances and appreciated them (indeed taught them to me). But perhaps being at the organ at the great hours, they were unable to detect the decline in quality of the psalmody at those times, compared to the unaccompanied little hours. Q.E.D.

Would it matter if the accompaniment were (inter alia) doubling the chanted melody or singing a separate voice?

Depends on whether we're talking about choir or congregation. Earlier in the discussion, @m_r_taylor recommended not doubling the melody when accompanying chant. I have a friend who absolutely insists on not doubling the melody. I've experimented with it some myself; as organist-choirmaster, it is possible to accompany with left hand and pedal, and conduct with the right, so that is an advantage.

On the other hand, congregations accustomed to accompaniment often rely heavily on the organ. I've found this to be even more so the case in Europe. I was present at a Mass in a packed cathedral (thousands of people) where Credo III, sung in alternation with a choir of treble voices, came to a grinding halt because of a wrong chord from the organist.

In my experience, the biggest challenge in congregational singing of chant is getting them to slow down as they approach full bars. The tendency is always to barrel on ahead. It is unhelpful when the next phrase begins on the same chord, because the only indication of the rhythm is the melody note. I've had to rewrite a few spots in the Bragers and Rossini accompaniments to give the organ a little more leadership in that respect.

Earlier in the discussion, @m_r_taylor recommended not doubling the melody when accompanying chant.

Just to clarify my statement, that wouldn't be my choice all the time, but I would definitely consider doing it in the case of a single cantor who was singing from the loft when accompaniment was expected/required.

Not more music, just good music that is not repetitious. If most of what you do sounds alike you need some new material.

I don't have a problem with lightly accompanied chant if it is done well. I rarely (if ever?) have found that doubling the melody on the organ amounts to 'doing it well', but maybe I haven't met the right organist. (Those who have accompanied me do not double the melody, and I've found their accompaniment to be exemplary and not to have led us in a bad musical direction.)

@Chris Garton-Zavesky

4) The word "Alleluia" can be treated in many different ways: in the Communion antiphon, for example, the first alleluia after "fidelis" begins on an ictic note in a group of three; the second alleluia begins on a non-ictic last-of-three (a weak up-beat).

So true! I find, as a singer, that one of the greatest joys of the Easter season is encountering so many different forms of 'alleluia' in the propers.

It is the tendency of musicians to long for "mo' MUSIC!!" That's not always a feature.

Many musicians do seek novelty, that's for certain. But the current craze here for unaccompanied chant is sort of an aberration, too. After all, we have only had accompanied chant for a thousand years or so. Then there is the mainstream approach which junks both chant and organs. Dare I say that what one encounters here is neither mainstream nor any kind of norm?

Charles,

Perhaps chucking our organs, wreckovating our parish worship spaces, and abandoning our musical heritage have all contributed to our inability to accompany chant well.... and thus the development (by way of compensation) of the preference for unaccompanied chant?

The sample size of churches actually attempting chant right now is comparatively low; if it were much larger, perhaps we would see far more natural variation in practice. Just a speculation.

a certain Order of priests commands that the organ play during any 'dead spot.'

OFMs, by chance?

MadO: no, not OFM. Think French....

The best chant accompaniment I have ever heard was on a pilgrimage to Pluscarden Abbey in the north of Scotland. One of the monks provided a light, sparse accompaniment (no pedal) to the Ordinary chants sung by the community and congregation. Just enough to keep everyone together. He left the Propers, sung by the community, strictly alone.

>> the chilluns' Mass did have accompaniment, but that was because the music teacher's voice was SO AWFUL that she dared not lead the singing without leaning on the organ for pitch. In every other regard, the woman was a saint, by the way

and in this regard too, I dare say. The music director who has that much humility is pretty rare, in my experience.

A weed is a flower out of place, after all

They both can make you sneeze.

"everything tastes better with ketchup". :

If it's church food, the ketchup definitely helps.

Greatest instrument.

https://www.youtube.com/watch?v=qtf2Q4yyuJ0