Maybe I’m a bit slow, or maybe the details of liturgical music are really complicated, but here is the truth: it took me years to figure out the relationship between the “Responsorial Psalm” that I know from the ordinary form of the Roman Rite, and the “Gradual” from the extraordinary form of the Roman Rite. This is complicated by the oddities of language. There is no “Responsorial Psalm” in the old form so it becomes difficult to trace its lineage. It occurs where there Gradual (which is also a Psalm between the readings) once occurred. The term Gradual is complicated by the fact that the book that contains all the sung propers of the Roman Rite is also called the Gradual or Graduale Romanum.
The structure of the two Psalm forms is completely different. The Gradual is for reflection. Time stands still. There are long elaborations on single vowels. It is a time for prayer. The Responsorial Psalm, in contrast, has typically asked the congregation to engage in a sing along with the cantor, usually consisting of an instantly repeatable antiphon, something closer to what we might experience in the Divine Office. But, as everyone knows, in our culture and times, the Responsorial Psalm has become the most musically unfortunate event at Mass. There are ways around it, such as using the Chabanel Psalm, but generally the Psalm at Mass has not fared well under the new form.
All of this is clear to me now but it took a long time to sort it all out. Which reminds me: we still have no easy reference book that explains the relationship between music and the ordinary form of the Roman Rite. Don’t you find it incredible that after 40-plus years, no such book exists? There are several reasons: confusions, complications, and too many open-ended options. As a result, most musicians are deeply confused and end up just relying on the missalettes for guidance.
In any case, let’s take this apparatus one step further. The Gradual can be sung in the ordinary form but rarely is. Further: it need not be sung in chant only. There is a long history of polyphonic Graduals. It is extremely rare to hear these masterpieces in any form of the Roman Rite. The Colloquium actually featured one by William Byrd. And here it is, followed by the Alleuia. It is absolutely magnificent. It so happens that this occurred in the extraordinary form but there is no reason why this could not have been sung in the ordinary form. There is a substantial distance between this and, e.g. Respond and Acclaim.