Possible Clues:

• Arrangement of this music could leave creator hanging
• Sacred performance changing rate, or otherwise
• A Grecian throng reworked religious song
• Silly charging a tenor for old song
• Organ teaching possibly involves source of religious music in church
• Monophonic unaccompanied sacred song
• In composition changing to rare variety of plainsong
• Plainsong introduced by a pope in the sixth century
• Singing in the abbey, received constant upset with Scot's crack about top note
• Medieval plainsong