As always, I note the kind contribution of Richard Chonak who translated the Latin original of the second edition (1988). Today, we look at the situation when there are two readings, not three, in the Liturgy of the Word:
9. When there is only one reading before the Gospel, the Gradual Responsory is sung after it, or the Alleluia with its verse. In Paschaltide, either one of the Alleluia chants is sung.
10. At the singing of the Gospel, after the final proper cadence, the conclusion Verbum Domini is added, as notated in the common tones; then all respond: Laus tibi, Christe.
For a weekday Mass, sing the Psalm or the Alleluia. During Easter, sing either Alleluia chant.
11. The Credo is sung in the customary manner either by all or in alternation.
12. The Universal Prayer [Prayer of the Faithful] is carried out according to local custom.
I’ll state the singing of the Credo has always been a mystery to me. For the faithful to state the faith: this seems a spiritual priority, and if a musical setting can enhance it, well and good. But if the musical setting were in any way an obstacle, the sung version should be dropped.