HENEVER a psalm tone termination has two accents, beware! These are often the more tricky ones. Mode 7 is an example, and even after all these years I’ve never heard a convincing explanation as to why the proper way doesn’t go UP on “non.” Doing so would give us a true accent instead of a fake one—although fake ones are allowed when there is no other choice. But that’s just not how it’s done:
I suppose it all boils down to whether one believes a 1-syllable Latin word truly has a “tonic accent.”
Mode 3 seems to do the opposite:
Yet Mode III does not do the opposite for something like: “Qui fecit caelos in intelléctu: * quóniam in aetérnum misericórdia ejus.”
And Mode III does not do the opposite for something like: “Et qui abduxérunt nos: * Hymnum cantáte nobis de cánticis Sion.”
Again I ask: How much do they really care about the accent? It would seem they do not consider a monosyllable a “true” accent worth preserving.
By the way, this handy Psalm Tone Chart includes numerous examples.
There is also valuable information in the 1957 Solesmes Mass and Vespers.
Even Mode VIII can be tricky—as has been demonstrated.