I am not a musicologist, so I'm can't really comment on issues such as what is or isn't known or what should and shouldn't be considered accurate historical performance practice.
What concerns me, though, is a particular way of thinking about historical performance practice which I think is wrong in itself and which is related to a very wrong way of thinking about liturgy and its historical development.
The "wrong way" (in my opinion) is expressed by forum user 'pulchritudo_musicae' (who is, apparently, Amy Danielle Waddle, the author of the original Sacred Music article that sparked the discussion). I don't really believe that she thinks exactly what her statements seems to say, so I want to focus just on the statement as a manifestation of a certain way of thinking, whether or not ADW holds that mindset or not. She wrote:
it is our duty and responsibility to try to determine the most accurate way to sing, the most accurate style, the most accurate notation [ . . . ] the task before us as scholars and as musicians to determine what chant should beI think this notion that there is some accurate or correct ideal performance practice is wrong-headed, and that it is a manifestation of a modernist way of thinking which has, in other areas of the Church's life, been destructive.
Moderns have a tendency to fetishize historical accuracy, cloaking a reactionary retreat into the past in the guise of intellectual progress.
This began in the Renaissance with the attempt to restore some perfect past version of Latin (that of Cicero). That project killed Latin as a conversational language among international academics, and halted the ongoing development and creation of new, and yet authentic, Latin liturgical texts.
At the same, the revival of Classical thinking and the adherence to Classical authorities in early-modern academia caused a substantial loss of Medieval philosophical and scientific development. While contemporary secular culture considers this period one of enlightened progress, the fact is that these Classicists wanted nothing more than to 'turn back the clock,' abandoning over a millennium of real and steady progress.
(And when Protestants, the spiritual children of the Renaissance, had the opportunity to write history, they swept all this under a rug of anti-Catholic propaganda, coining terms like "The Dark Ages" for a period of almost unparalleled freedom, stability, and intellectual progress. But, I digress...)
In the 20th century liturgical movements we can see first the liberal resourcement that wanted to strip away eighteen centuries of development in favor of some imagined "Early Christian Community Meal" (in exact parallel to the early-modern idolization of Classical philosophy). Then, later, a generation of naive traditionalists seemed to imagine that everything was wonderful before the Council and that history ended sometime in the Baroque era - rejecting false progress in favor of false nostalgia.
But history doesn't work like that. And working performers - singers, directors, actors, dancers - know especially that the performing cannot be properly understood this way.
Any particular performance of a chant - or, really, any piece of music - is a unique event on its own AND ALSO is part of the tradition of that piece's history. The first performance is not a 'Platonic' standard, with subsequent performances being merely re-enactments or instantiations of that single ideal.
When this notion of a past ideal and present re-enactment becomes normative in an artform, the results are usually disastrous and (Peter Brook would say) deadly. Opera, for example, suffers from this in many places. Ballet as well, and - to a lesser proportion but a greater quantity - Shakespearean theatre.
And this way of thinking, which is deadening to the performing and practical arts, is equally dangerous (perhaps, moreso) in liturgy.
The sacrifice of Calvary and the self-giving nourishment of the Last Supper are not simply remembered or re-enacted in the Mass, with the historical events standing behind us as Platonic ideals or as dramatic inspiration. Rather, the sacrifice is made entirely present and new in each Mass throughout history - even as it is the same sacrifice, offered once for all.
Because we cannot allow this deadening spirit to inform our understanding of liturgy, it is important that we guard against it in performance culture generally and especially with regards to the music which is so integrally a part of our liturgical heritage.
And I want to make clear that I am in no means suggesting an anti-intellectual approach to chant and liturgy, or that I would encourage an abandonment of the historical and musicological study of these things. Rather, I simply believe that we must keep these things in their proper perspective.
Historical scholarship is important. It is good to know what people have done in the past. It is worthwhile to preserve and work within the tradition, and worthwhile to revive traditions which have fallen out of practice. We should never approach music in a haphazard, "do whatever I like" approach, but humble ourselves and recognize our place within a tradition that has gone before us for a thousand years and will most likely survive us for another thousand.
At the same time, we shouldn't let the virtues of historical and musicological scholarship become idols, and we should guard our theoretical frameworks, lest we let our academic pursuits become a deadening force on the liturgy and an impediment to the recognition of God's all-present and life-giving grace in the sacraments.