This is the first study to examine the seven invitatory antiphons of the Birgittine weekly Office, the Cantus sororum, offering complete transcriptions of the melodies and texts. An important general finding is that these invitatories share many melodic similarities with great responsories, but on a more detailed level this article investigates precisely how these chants relate to known models, both complete melodies as well as individual melodic motives. Four patterns of composition among the Cantus sororum invitatories emerge: (1) unique texts may be combined with melodies that resemble other known chants outside the Cantus sororum; (2) texts and melodies that resemble other variants outside the Cantus sororum may be combined in new ways; (3) both text and melody are unknown outside the Cantus sororum.
Overall, these invitatory antiphons, like the rest of the Cantus sororum, represent creative work with existing melodies and texts, including reworkings, borrowings and consistent use of melodic motifs, comprising a significant part of a repertoire at once distinctly Birgittine in character and yet conforming to the common stock of Gregorian Chant. Melodic correspondences within the Cantus sororum as well as in the Birgittine Mass repertoire thus afford an interesting perspective on a soundscape in which the Birgittines functioned and where, through music, their identity was created and maintained.