Here we have two recordings of today’s Communion chant, Laetabimur. The first, from St. Benedict’s in Sao Paolo, Brazil uses the organ to provide a harmonic accompaniment:

When we performed this chant today at the French National Church in San Francisco, I decided to use an organ drone:

Neither of these practices is justified by the notation itself, so I cannot make an argument for or against their “historical authenticity” based on manuscript evidence. But I will ask, does the addition of the organ help to bring rhythmic vitality to the chant, or does it stifle the suppleness of the Gregorian composition?

For those interested in chant accompaniment, there’s no better online resource than the Leland Library of Rare Books, which also hosts a number of treatises on the subject.  If nothing else, these collections provide valuable insight into various rhythmic theories that have been in practice in the previous two centuries.