The paper explains the medieval notions of tonary and differentia in theory and practice. Both notions played a prominent role in defining the book type tonary as well as the function of melodic cadences called differentiae. The tonary is important for the examination of early plainchant repertory and for the interpretation of medieval mode theory (Octoéchos). The differentia has already been discussed by Peter Wagner as the most exciting element of antiphonal psalmody. Recent comparative studies of theoretical as well as practical sources of tonaries are highly promising.
The conflicting assignments between modes 3 and 8 is found not only among sources, but also within a single source through erasures and revisions in different hands. Here the modal assignments of office antiphons are examined through a comparison of the sources of the monasteries in the region of Lake Constance. They are from the monasteries of Einsiedeln, St. Gallen, Rheinau, Weingarten, and Zwiefalten. For a singer, the most important matter in singing antiphons was not to end the melody on a specific note, but to select a suitable reciting tone. At a time in which musicians classified antiphons into several “differentia” groups, what characterizes each differentia group is surely the melodic incipit and the psalm tone. But over the course of time, medieval musicians became to consider the concept of mode, that is, the classification by the final note and range, and at that time the ending of the antiphon gained in importance. This change of thinking gave rise to the modal conflicting assignments.