Our schola is learning the Requiem Mass from the Liber Cantualis, and in the Communio "Lux Aeterna" I'm puzzled over the final phrase "Cum sanctis tuis in aeternum". Is this sung after a repetition of the initial "Lux aeterna, luceat eis, Domine", is it simply sung straight through as is, or is there some other method that I'm not seeing?
Gregp: Yes, the usual way, also given in the Liber Usualis, is to sing this straight through as written. The verse 'requiem aeternum' with the reprise of 'cum sanctis tuis' is a vestige of the ancient practice of singing psalm verses and repeating the antiphon.
Usually these days, the communion takes longer than this music if the congregation is receiving. If you would like the communion chant to last longer, the Communio book (also pdf files on the CMAA website), gives additional psalm verses you can use. That resource shows options of repeating the full antiphon 'lux aeterna' or just the ending phrase 'cum sanctis tuis.'
As indicated in the Graduale Triplex, not only additional verses, but other optional psalms may be used with the various Antiphonae ad Communionem for the Funeral Mass. So instead of the verse "Requiem aeternam dona eis Domine, et lux perpetua luceat eis" and its following verses, you might choose verses from Ps. 129 or 120 or 22.
Both the Gregorian Missal and the Graduale Triplex show the traditional antiphon in its entirety as "Lux aeterna luceat eis, Domine, cum sanctis tuis in aeternum, quia pius es." In addition, both sources suggest numerous other optional antiphons for the Communio.
Thus, for the OF you have a choice of antiphon and a choice of psalms and verses to fit the occasion. Of course, there is nothing wrong with singing the traditional Communio as in the Liber Usualis.
For Lux aeterna, the verse "Requiem aeternam" is the concluding verse of the whole psalm, replacing the Gloria Patri in Requiem Masses; so its notation in the chant book is the vestige of a complete psalm, just as the Gloria Patri is at the introit.
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