T
here are three main streams of how to interpret the rhythm of Gregorian Chant. The Chant was invented some twelve hundred years ago, and has gone through tremendous changes in how it is performed. Notably, Gregorian Chant only developed written notation hundred of years after its earliest development, and this notation has had its own evolution as well. Making sense of of these elements, even before touching on how the purpose of chant influences its performance, is no simple task.
By far the most popular rhythmic interpertation of the Chant is the Solesmes Method, pioneered by the monks of the Solesmes Abbey in the late nineteenth and early twentieth centuries. The monks, (led initially by Dom Pothier, and later crystallized into its modern form by Dom Mocquereau) were attempting to reconstitute the Gregorian Chant, which had devolved considerably from the middle ages through to the modern period, into a form unrecognizable from its original performance. The Monks of Solesmes put forward a great, decades-long research effort to discover the original meanings of the Chant Notation, ultimately landing on the idea of "free rhythm", in which notes are freely grouped into sets of two or three "beats", which defines the rhythm of the particular chant. The books produced by the monks are extremely widespread, and if you hear Gregorian Chant being sung, it is almost certainly using their techniques. I myself sing using the Solesmes Method, and find it artful and satisfying.
Developing further in the twentieth century is Semiology, pioneered by Dom Cardine (also of Solesmes). The disciples of Semiology believe that the gregorian notation, even of the most ancient and reliable sources we have, is woefully inadequate to understanding how the Chant was originally sung -- they believe that there was an enormous amount of musical information "taken for granted" and considered so obvious as to never be written down by the monks of old. Therefore, Semiologists first embrace the idea that we cannot reconstruct perfectly a version of the Chant that has disappeared, but secondly, that Chant must be understood in terms of recitation of a text, not just as a pretty song. They therefore use rhetorical techniques, as well historical and textual analysis to inform their performances. I find Semiology a bit intimidating, but some of its adherents produce probably my favorite sounds of Gregorian Chant, generating truly mystical and surprising experiences.
The last major "school" of rhythmic interpretation is Proportionalism. Proportionalism holds that the monks of Solesmes completely missed the basic unit of rhythm in the notation, which is that there is a steady beat throughout the music, and that all notes are divided into two classes; one short, and the other long, being exactly twice the length of the short note. Proportionalists believe that Gregorian Chant is descended from Byzantine Chant, which has this kind of steady rhythm, in contrast to the "free rhythm" of Solesmes and Semiological Methods. There are not very many proportionalists, and consequently not many recordings of their technique. What I have heard (and tried to work out for myself) is not my favorite of the Chant interpretations, but I do find their historical and musical reasoning rather convincing.
Where does this put us? Which of the methods is best, or best to be used? What is the actual purpose of the chant, and what is the purpose of trying to re-discover its original incarnation? This is too big a topic for me to cover right here, but I'll return to it later. Chant is the way the Church prays. May we strive for it to please the Lord.