is the liturgical book or section of a book that contains chants for the ordinary of the Mass. Until the 16th century, such material could be found primarily in the appendices to graduals, or in collections of tropes or sequences (Liturgical books). During the 13th century, the chants of the ordinary were brought together, largely without their tropes, in individual cycles that marked the liturgical rank of the feast days. In the modern Roman kyriale (1905–1974), there are 18 such cycles and a few chants ad libitum.
Graduale Romanum, 1974