Certain disciples of the new school, much occupying themselves with the measured dividing of beats, display their rhythm in notes new to us, preferring to devise new methods of their own rather than to continue singing in the old way. Therefore the music of the Divine Office is disturbed with these notes of quick duration. Moreover, they hinder the melody with hockets, they deprave it with discants, and sometimes they pad out the music with upper parts made out of secular songs. The result is that they often seem to be losing sight of the fundamental sources of our melodies in the Antiphoner and Gradual, and forget what it is that they are burying under such superstructures. They may become entirely ignorant of the ecclesiastical modes, which they have already ceased to distinguish, and the limits of which they abuse in the prolixity of their notes. The modest rise and temperate descents of plainsong are entirely obscured. The voices incessantly rock to and fro, intoxicating rather than soothing the ear, while the singers themselves try to convey the emotion of the music by their gestures. The consequence of all this is that devotion, the true aim of worship, is neglected, and wantonness, which ought not be eschewed, increases. We hasten to forbid these methods, or rather to drive them more effectively out of the house of God than has been done in the past.

Pope John XXII (1245 - 1334)

Nevertheless, it is not our wish to forbid the occasional use of some consonances [i.e. polyphony], which heighten the beauty of the melody. Such intervals, therefore, may be sung above the ecclesiastical chant, but in such a way that the integrity of the chant remain intact and that nothing in the prescribed music be changed. Used thus, the consonances would, more than any other music is able to do, both soothe the hearer and inspire his devotion, without destroying religious feeling in the minds of the singers.