The book provides an astounding level of detail about this extremely interesting event. Among other interesting facts: there was another Graduale that came in 1908, one produced by the monks of Solesmes under the care of Dom Mocquereau. Putting the two side by side, we can see that the Vatican Edition is comparatively unwieldy, oversized, expensive, and it did not hold up well to wear. The Solesmes edition is more compact and more durable, even though it used less fancy materials in the production. It was also more affordable.
Most famously, the major difference between them concerned the addition of small rhythmic signs in the Solesmes edition. The notes that called for the "mora vocis" were explicitly marked by a dot, whereas in the Vatican Edition the eye had to read the space between the notes. The expressive notes were marked by a line on top called the episema. The neumes themselves were marked with an "ictus" to delineate groups of notes (just as modern music has measure lines to organize notes).
The purpose of these markings were to make explicit what was only implicit in the Vatican Edition (Jeffrey Ostrowski explains all of this in the Winter issue of Sacred Music, forthcoming). This was seen as an aid to more quickly getting singers on the road to good chant performance and to keep singers together. With the rhythmic aids, singers were able to move forward through the chant in a uniform way, without being dragged along by a single voice leading everyone around. An analogy might be to compare cars at a stop light (each car is cued to move forward by the behavior of the car in front) with a marching band (everyone moves together because they all accept the same assumptions about what is to happen when).
But why two editions? One might suspect that there were some tensions between the groups working on them. Tension is one way to describe it. Another would be Cold War, one that makes today's disputes seem mild by comparison. There were intense disputes that lasted for more than ten years. They concerned the methodological priorities of two great champions and masters of the chant: Doms Pothier (once at Solesmes but then residing in Rome) and Mocquereau (who was the master at Solesmes).
The dispute concerned whether and to what extent the chant should be restored to its "golden age" status or whether the modern editions should accommodate development that had occurred over the intervening centuries. Mocquereau tended toward the former position while Pothier tended toward the latter position. As time has past, the Mocquereau position on these matters seems to have prevailed both in terms of art and scholarship.
There were two separate but related controversies, the first over the use of rhythmic signs to aid in singing and the second over copyright to the editions themselves.
The copyright issue was gravely and wickedly unfortunate, and seemed to bring out the worst in everyone – as one might expect of any conflict in which state edicts are involved that concern three separate countries (France, Vatican, Belgium) and tremendous confusion over who owned what.
The rhythmic issues were more substantial, but more easily resolved since Mocquereau agreed to defer to Pothier in wanting to exclude them from the Vatican Edition, even as he gained assurance from the Pope that Solesmes would be able to produce its own edition.
In the end, the Vatican Edition owes so much to Pothier who had prepared most of the chants, to Mocquereau whose scholarly defenses of the reconstruction effort were second to none and who showed the merit of his rhythmic theories by raising up the greatest scholas in the world, and also to Pope Pius X, who had great confidence in Solesmes and Mocquereau personally.
What I find striking is how it was the Solesmes edition, and not the Vatican Edition, that came to prevail in the marketplace, for its ease of use, its longevity, and its accessibility.
