This is Why We Use Ictus Markings:

I got several very helpful replies on the CMAA forum in response to my query... here are a few of the helpful reasons why we use the ictus markings in Gregorian chant:

We mark ictus locations because it helps us stay together perfectly.

A chant line should have shape. You cannot give shape to something that does not stick together. Marking locations of ictus provides singers with a sense of what binds the chant line together. Instead of singing 1-1-1-1-1-1-1, you come to see things like 12 123 12 123 12 1... Experience suggests that better legato singing will result.

Also, marking ictus helps to provide bouyancy to the chant. There is a tendency in some singers to hammer away at text accents as if they were bludgeoning cats. Talking about "upbeat" and "singing smoothly over those 12 12 12's" helps to keep the sung line afloat, as it were. It helps to mitigate against ponderous accents.

So there are two reasons, at least.

I do plan to use the "bludgeoning cats" illustration in the future... I got a good laugh when I read it! Here is another:

The ictus also marks the beginning of a gesture which can be described as either arsis or thesis. Of course the large-scale shape of the phrase, or of the entire chant, is probably of greater importance. But having these subtle shadings of rising and falling, elan and repos, keeps the musical line in motion at every small step along the way.

The main reason is that it provides a method for counting through the chant, which gives an idea of forward direction. to me, the main advantage is that it prevents getting stuck or slowing down.

yes, the forward motion is important in music.

Yet another:

So ictus is as essential as solfege. (It's just more subltle to realize that.) It's the rhythm that gives music 'life.'

From a friend I met at Chant Intensive:

By the way our schola is learning Communion chant "Qui manducat,' which I love.(The text is really the core of our faith, and the music is so beautiful. I can talk about this forever.) We listen to Stepping stone Cd and another one by a famous group who I believe in a 'different style'. We all agreed that Stepping stone sounds better than the other. The other had too much contrast of long pause and the fast notes for neums, I think. Too much contrast of musical elements seem to be not quite right in chant singing. (Another advantage of ictus. Control of the rhythm, not sounding random. I hope this is not starting another heated discussion of the two different styles of singing chants.(although I learned a lot from it.) It's just my opinion)

You are 'lucky' that your group don't mind solfege. I had a long talk about it, because a couple of members in my group believe that they don't need it. They say that they always sang songs just by ear (one is in a folk group also.) and they can get by. Spending time and effort on learning solfege is more than what they want to do. (Another words, music is just a music. It can be that serious.) Well, I guess I'm too serious that I spent all my life learning music, and I still have so much to learn.

Another friend from Colloquium and Chant Intensive:

It's so tempting to answer "because I say so," the way one's mother did. It is all about forward movement in chant. I haven't broken the "ictus bad news" to my schola yet because the solfege whimpering has to die down to a respectable level and we're getting ready to sing on Candlemas.

It is my recollection that Scott suggested initially delivering already marked-up music to your singers, particularly if time is an issue. Actually, I think they'll be happy to sing 1-2,1-2,1-2-3, etc. after their weekly dose of solfege.

OK, so I shall try again this week to convert the nonbelievers to believing in the usefulness and beauty of Gregorian chant rhythmic markings this week... wish me luck.

Here is a short excerpt from the Parish Book of Chant (p. 175) regarding rules for assigning ictus locations (in order of precedence):

1. as indicated by the ictus mark (Don't change the monks' markings!)
2. as it falls at the beginning of a long or doubled note: (look for those pressus locations)
3. as it falls on the first note of a neume
4. by counting backward by twos from the next known ictus.

There were three others given to us by Scott Turkington at Chant Intensive -- they came originally from the book by Dom Gajard:

5. as it falls on the last syllable of a word
6. as it falls on the 1st syllable of a dactyl (a dactyl has the accent on the third syllable from the end: ex. Dominus or Gloria)
7. off-ictus accent

Next time maybe I'll post my chironomy rules... what fun.