I have a very different attitude than many here. I firmly believe that a Gregorian schola should overlap with a choir (be it SATB or otherwise, e.g. men's voices only) in terms of membership, but they need not overlap entirely and not at every liturgy. That means following the Mass, and things like the bows for the Holy Name should be observed, whether you are at the front (in the choir/sanctuary), on the floor somewhere, or in the loft (or divided, depending on the occasion, say with cantors in the choir and the rest of the men elsewhere). Personally, I think this should be the case even if the people doing the most work on a given day (like someone cantoring solemn Vespers) is paid a stipend just like a polyphonic rehearsal or Mass call, and it avoids the handling of the choir from becoming too concert-like and professionalized in what I consider the wrong way, especially if you're trying to build up a schola filled not just with good or even excellent singers but faithful Catholics.

In polyphony, this is not possible due to the length of the phrases, never mind the technical aspects, and you have to reach out to paid singers from the community who may or may not, depending on the circumstances, be faithful Catholics, especially at first.

Also, the problem of the bows is why I am a big fan of alternating at each strophe of the Gloria and Credo, either women/men (depending on whether you have a woman's schola of any kind as well) or men/all (either a cantor or the men of the schola together), and while this is good to do in the Pauline rite for aesthetic reasons (IMHO anyway…) it is all the more so practical in the traditional form and are conscientious of the prescribed gestures. That is, in the Gloria and Credo, you only have any one group bowing for about half, so Adoramus te, Gratias agimus tibi, and Jesu Christe are sung by one group, then suscipe deprecationem nostram and Jesu Christe by the other), and the same for Jesu Christe and simul adoratur.

Now, practice varies somewhat for the genuflection in the Credo, and the exact mechanism of the bows will vary depending on the positioning of the schola and of the direction (I can't recall what was done the last time I was at a Mass sung by a schola composed of one of the ex-PCED communities but I can say with certainty, having watched a short video from Randol Abbey in France (one of the trad daughter houses of Solesmes via Fontgombault) that they do indeed bow profoundly for the Gloria Patri of the Introit according to the monastic custom.

Obviously there are fewer bows in the NO, and in the traditional form some are barely noticeable nods (like the Alleluia of St Michael or several Vespers antiphons on the same day…), but I think the general point still stands, though I admit that I have a very different perspective on this than most people here.

Piety and showing honor to God far outweighs the meager sacrifice of 'proper musical posture' in not doing so.

UPDATE

I am saying this because the phrase is very small and probably doesn't make much of a difference in 'musical excellence'.

When you are singing in a schola or a choir, the act of music making becomes your spiritual offering. While it is certainly fine to bow the head at the name of Jesus in general, if hardly seems necessary (or even appropriate) if you’re in the middle of singing ‘Jesu salvator mundi’, for instance. Kneeling for the great amen (presupposing it is merely a changed response and not a florid polyphonic setting) or even the mysterium fidei is hardly offensive to the music. I ultimately think that these things simply require a degree of prudence. You can nod your head slightly without facing all the way down to the floor, or you could even gently bend a knee (à la very mild curtsy) rather than bow the head, while singing a motet. But if people are bowing so much that they are literally facing the floor and altering the sound of the choir when they are supposed to be singing, they are being too grand with their gesture and it becomes inappropriate. Our Lord would certainly know if you make an act of reverence in your heart even if you don’t nod your head while singing.

When I play in the Ordinary Form, the Memorial Acclamation is either done unaccompanied or with just the melody doubled so that I can remain kneeling next to the organ between the end of the Sanctus and the Doxology.

There is nothing irreverent or unseemly about standing during the Canon

In the east, we stand with the risen Christ as the Council of Nicaea decreed. Standing is fine even in the west. The Latin Rite priest where I worked maintained that standing, sitting, and kneeling were all valid options. He generally knew his canon law quite well.

Generally speaking, the postures taken by the faithful at Mass are matters of common custom, not rubrics. And it is also always important to avoid scrupulosity: otherwise everyone would be crawling on their knees to the altar rail, rather than doing the sensible thing and walking like a normal human being: yes, God is awesome, omnipotent, and all-holy, and we should owe him due reverence, but he is also a God who "humbled himself to share in our humanity". And, if we are supposed to give God our absolute best in Worship, with the finest vestments, vessels, art, and music, then the execution of that music ought also to be the best we can do, and this includes proper posture to enable proper vocal technique: the act of singing in itself should be a prayer just as much as the words being sung, standing is and always has been the normative posture for worship, especially in sung liturgy, e.g., the psalms of the office are supposed to be sung standing, Rome permitted sitting during the psalmody much in the same way Moses permitted divorce.

Umm, actually it does, Chris. Fr. Fortescue mentions in The History of the Roman Rite Described that the lay people in the body of the church "enjoy a certain natural liberty".

Richard Friend talks more about this at length in an article about the topic from Rorate Caeli:

https://rorate-caeli.blogspot.com/2016/04/an-essay-on-postures-of-congregation-at.html

Stimson,

Something got lost in translation. I agree with you that in the old form, the laity enjoy a certain natural liberty. Completely agree. No distance between your position and mine, so far as I can tell.
The more recent form, on the other hand, requires the assembled lay faithful to do this, and do that, so that someone can claim that, for the sake of unity, everyone must stand during the entire time when Our Lord is being given to the faithful.

[Palm smacks head: I've just seen what I wrote in the post to which Stimson addresses his comment. I have my letters backward. UA is more "free" than the UR, not the other way around.]

But the choir/schola cantorum when exercising its ministry is no more part of "the congregation" than the servers or readers are when exercising theirs, otherwise, the readers would have to sit when proclaiming the readings, and the servers somehow sit when assisting the priest at the offertory in order to "follow the rubrics": common sense needs to prevail. And if there is a lacuna in the rubrics regarding the choir, one needs to supply from tradition and Roman/Papal practice (romanitas): the former rubrics indicate that in the Mass and Office the choir/schola is to stand when singing, unless the contrary be indicated (e.g., kneeling during the final Marian Antiphon on penitential days) or permitted (sitting during the psalmody of the office); further, Papal practice seems to have the Capella Sistina standing through the whole liturgy; further, since recent legislation treats a lay choir/schola and a religious or clerical choir/schola equally (not to be confused with non-singing clergy "in choir"), rather than as a second class, it would be appropriate for a choir to utilize the former rubrics when necessary.

Now, on a practical level: my choir kneels when singing the Memorial Acclamation because it's so short, but stands for everything else, including the ordinary, proper, hymns, and motets; they bow their heads and the Holy Name (briefly, even if the word is prolonged on a melisma), and make a profound bow during the Gloria Patri at the Introit and Communion, it doesn't interfere with singing, but they are standing, as the schola cantorum should.

Thank you all for your replies,

I appreciate the diversity of answers.

One reason I ask: our choir (partly due to the acoustics of the church) requires microphones, and they are set behind the organ. When they are kneeling rather than standing, they are further away from the microphones and blocked by the organ. It would seem from just the mere physical, sonic situation, the requirement of standing is more warranted.

But as just a person in the pews, yes I agree with many of you -- there is no reason not to bow or kneel.

Concerning the choir though: while the primary aspect of worship is internal, are we not to give even in our outward conduct as the fatted lamb/GoldFranckincense&Myrrh/costly perfume? As the choir, is not the music itself our primary sacrifice? If so, should we not offer it as nicely and well done as we can? While their posturing might be different from the laity, I see no reason to read that difference as constituting an inherently different spirit of worship. (Like CharlesW said, the Byzantine Rite has everyone stand, albeit they bow at key moments.)

Yeah, but some of the congregants do. One of my choir members once told me some ladies in the front couldn't hear. I asked how old they were. When I got the answer, "upper eighties," I understood why they couldn't hear. The problem with microphones is that they are over-amplified far beyond what is necessary for hearing.

I have my fair share of warblers—I guess they have good technique!
*runs away giggling*

Charles,

Noting that some of us need hearing aids (I do), magnification of the sound for everyone, equally, doesn't help. I, therefore, conclude that it is better to not use microphones and speakers for singing, and to keep sermons blessedly (not unhelpfully) short.

Most sermons are not worth hearing to begin with.

Could you define "most"?

which is louder... a sermon or a canon?