Sometime in the last three decades of the thirteenth century, two medieval scribes sat down to write the melody for the song ‘Pour conforter ma pesance’ by Thibaut IV count of Champagne and king of Navarre, then some thirty years deceased. The one we may call scribe T was writing in the Artois region of France while scribe O was located further south-west, most likely Burgundy or the Isle de France. Despite their geographic distance, these two readings are remarkably similar in pitch, something which we might expect given the relative closeness of these scribes to Thibaut's time. But this is not so for their rhythmic interpretations of Thibaut's melody. Scribe O, who has a decided tendency to interpret trouvère songs rhythmically by indicating long and short values, has here abstained from doing so (example 1.1), while scribe T, who elsewhere does not give rhythmic values, has done so in this case (example 1.2); his reading clearly alternates long and short values, creating a rhythmic pattern called a ‘mode’ (modus) by medieval theorists. For some reason, for this particular song, both music scribes decided to change their habits, switching rhythmic camps, so to speak.