Whereas the melodies of the Ordinary chants of the Mass seem to have been rather few in earlier centuries, they subsequently developed and multiplied as a consequence of new modes of poetic invention (tropes and prosulas), their melodies taking into account the theory of the octoechos. Kyrie melodies provide us with particularly striking witnesses to this development. Despite their number, their diversity, and their classification in the octoechal system, almost all of the Kyrie melodies, at least until the end of the twelfth century, can be traced back to an earlier melodic formula, sometimes termed an ‘anaphoral chant kernel’ (CED, Gba, FGa), recognisable as a ‘signature tune’ of the Kyrie genre. This relates to Dom Jean Claire’s hypothesis about the E corde-mère as the nucleus in which the earlier Kyrie compositions originated. It also forms the focus of the protus authentic and deuterus authentic modes.