Taken from NLM
Can a choral Sanctus be sung according to the rubrics of the new missal? The most recent General Instruction on the Roman Missal seems to preclude this possibility.
But wait just a minute.
Some fine CMAA veterans to whom I am most grateful have unearthed an article from the Fall 2000 issue (vol. 127, no. 3) of Sacred Music writen by Duane L.C.M. Galles, a canon and civil lawyer. It explores the question of the choral Sanctus from the perspective of church law. Galles masterfully takes into consideration Canon Law, Sacrosanctum concilium, Inter oecumenici (1964), Musicam sacram (1967), and the General Instruction on the Roman Missal. He carefully sorts out the juridical nature of each of the most pertinent documents (e.g. forma specifica vs. forma generali; also the meaning of the term "instruction"), and untangles this seemingly impossible mess and comes to the conclusion that, yes, the choral Sanctus is quite permissible indeed.
The CMAA will soon make this document available online. Keep your eyes open.
Here are some excerpts to whet your appetite:
"(Musicam sacram's) article 34 foresees two ways of singing the Ordinary of the Mass, both a Plan A and a Plan B. Plan A is the case when there is 'part-singing for the chants of the Ordinary of the Mass (when) they may be sung by the choir alone in the customary way, that is either a cappella or with instrumental accompaniment.' Plan B is to divide the Ordinary between the choir and congregation in which case 'the Sanctus should as a rule be sung by the entire assembly along with the priest.' Musicam sacram thus provides as its Plan B for what is described in article 168 (of the GIRM. M.E.L.) as well as for a Plan A or polyphonic plan. This is perhaps why articles 15-17 of the 1975 instruction and articles 35-37 of Missal 2000 do not place the Sanctus (and certain other parts of the Ordinary) in the category of responses 'that the gathered faithful must contribute' or those 'assigned to the whole congregation called together.'"
"While canon 20 states that a later law derogates from an earlier one, a universal law does not derogate from a special one, unless the latter expressly so states. Here the 1975 or 2000 instruction forms a later general law and Musicam sacram forms a set of special norms governing sacred music. Thus we have the case contemplated by canon 20 and we may also note that Musicam sacram has also made provision--as its Plan B--for article 168. Since the latter general norm does not expressly abrogate Plan A of Musicam sacram, under canon 20 Musicam sacram's Plan A must be still lawful. This seems a true application of canon 20 and the result is reinforced by the approval of Musicam sacram in forma specifica."
I can't help but comment that it's very sad that we must work through so much legal jargon in order to defend a well-established practice in the Roman Rite. We should nevertheless be grateful to Galles for having taken the time to do so.
Still not convinced? One more snip:
"Furthermore, canon 21 says that where there is doubt whether a prior law has been revoked, revocation is not to be presumed but rather the later law is to be interpreted, so far as possible to harmonize it with the earlier one."
Let the Missa Papae Marcelli begin!