I don't know if there is a term for this, but it seems (to me) to occur so frequently that when I talk to my schola I want to refer to it as something other than "that figure that's on the torculus on the second line near the end". The phenomenon I'm referring to is a pattern of a lower note alternating with an upper note, and then the pattern is changed by going one note lower than expected.
Looking at the Introit for Christmas Day (Puer Natus), on the word "Angelus", the melody is la-do-la-ti-do SOL (instead of la again).
Likewise in the Gradual (Viderunt omnes), on the word "Deo" there's a torculus which goes la-do and then SOL.
In the Communion, "terrae", la-do-do SOL.
These are just the easiest ones I could find from the the Propers we were just singing, but I know there are tons of them out there, and they seem (to me) to be something very different from "modern" meoldies. In fact, it's one of the things that I can listen to and think, "that's a chant meoldy".
Am I nuts, or is this something I can point to and say, "Here's that X again"?
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