We are not protestants who twist in the wind and follow our every impulse. There is no “liturgy for a given congregation.” There is one holy sacrifice of the mass and there is music which supports it and music which does not. The mass is supposed to be solemn and reverent. It is not supposed to be chirpy, happy nor is it supposed to be about the congregation. Chant supports the liturgy in all situations. I am not saying that chant is the ONLY music which supports the liturgy, but I am saying that the suggestion that there are times when it does not - that suggestion is just flat-out wrong.
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I didn’t say that their was a liturgy for a given congregation, in the sense that there is somehow a different liturgy for each congreation. But any time a congregation goes to mass, they have a separate experience of the liturgy, not only from other times they have attended, but from other people attending. Even two people attending at the same place and time might have quite a different perception. One, who has never been to a Christian Church before, and is sitting behind someone in a large hat, might perceive little of the content and just be confused, or bored. The other person might find the opposite. That is not the fault of the people involved, or those who are responsible for liturgy, it’s just a result of being human. What happens at any particular celebration of the Mass can affect the congregation, the individuals, that happen to be there. That is why the physical trappings are paid attention to at all.
When you say that the mass is meant to be solemn and reverent, I would certainly agree, (although I would not always rule out happy - the Gloria includes the idea of supreme happiness and fulfillment I would say, at least that is my experience of it.) But you cannot say that it should be solemn and reverent, and then say it is “not about the congregation.” Well, if the music and other physical adjuncts to the liturgy are not working to instill solemnity and in reverence in the congregation, who is it that is meant to be solemn and reverent?
I am not sure what you are meaning when you say supports the liturgy, because it does not seem to be what I mean, and I can’t see what you are trying to get at. You say it always supports the liturgy. So, you mean it always works to give the right kind of solemnity and reverence? Since you say the response of the congregation is not an issue, I do not understand how you are assessing that to be the case? Do you mean it is reverent according to God, or some abstract measure?
I would say it supports the liturgy if it works toward helping that particular group of people sense the true meaning of the Mass. If it actively causes difficulty even after a period of adjustment, then it does not support, but undermines it. I do not think it is possible to say there could never be an individual person for whom chant was a difficulty, nor could one say it could never be true of a congregation.
But perhaps one of the relavent documents that are being discussed says that chant is always appropriate in every situation, or that it always supports the liturgy in a positive way? None sticks out in my mind, but I may have missed something.