We do on occasion. As long as the Proper is chanted, other music is at your discretion. I've never seen any edict against it. If it's Low Mass, it could even be in English. We do that as well.

Thredboskier345,

There isn't a rule against such a thing, to the best of my knowledge, but certain principles do apply.

1) At a sung Mass (of any degree, I think) the Propers and the Ordinary take precedence over any other music -- so before we add the Vespers hymn, the rest should be chanted -- even if it's recto tono.

2) The singing of the Vespers Hymn would need to not unduly prolong the Mass. (If you keep the action of the Mass delayed because you're busy doing "extra" stuff, this is not proper, but a polyphonic ordinary doesn't violate this principle, because you're still singing the Mass.

3) Rationally (but I don't know if there's a decree to this effect) the Vespers hymn, whenever it is sung, would have to be proper to the season, at least. So, we couldn't sing the Vespers hymn for Paschaltide in Septuagesima, just to use a silly example.

4) Some people argue (and I tend to agree with them, at the cost of bushels of scorn heaped upon my head, because I remember reading an official document to this effect) that nothing in the vernacular belongs between the initial sign of the cross and the Last Gospel, at a sung Mass. Low Mass with hymns, which should be exceptional, if I recall correctly, allows vernacular hymns.

(4) is something for which I am flexible, at Communion especially. Fine, it is increasingly an integral part of the liturgy even in the TLM world, but there might be a time where a vernacular hymn works well. No one died at Christmas when the choir sang “Stille Nacht” in German at communion during the solemn Mass during the night.

We usually sing Office Hymns at our TLM, both after the Offertory Proper and during Communion. We usually try to find a Hymn that fits either the Season e.g. Christmas, the month e.g. Sacred Heart or a Hymn for the Saint of the day.

Depending on the melody and metre most 5/6 verse hymns will fit in the time available, longer Hymns are sometimes needed for Communion, the Ambrosian 9 verse Vesper Hymns are quite good for this.

When the Mass is highly festive (1st class) and occurs at weekend or holiday with a numerous attendance, sometimes I program for Communion/Ablutions the Comm. antiphon, the Vespers hymn of the Feast, followed by the Magnificat antiphon and Magnificat itself, in alternatim with polyphony or organ versets. It's a 10-15 min program, depending on how long is the hymn and the alternatim versets, but a very beautiful of liturgy music, performed as cantus varii sequence.