Continual Change.

It is tempting to view something as old and formal as the sacred liturgy—the Mass and the Hours—as immutable, with a body of works and system of practice that has remained unchanged since it began. Nothing can be further from the truth. The entire liturgy, both its format and repertory, was in a constant state of flux throughout the period. New compositions and ceremonies were added, older items were revised and altered, and regional variants of all types arose and were suppressed all during those centuries. Discussed below are some of the major changes that came about during this period involving music, although there were also numerous changes to the prayers and the format of the ceremonies themselves. The inclusion of musical drama, the addition of new chant items and devotional works, and the application of...