SCHOLARS TODAY generally agree that ‘isorhythm’ ought to mean what it says, a term describing segments of music literally exhibiting the ‘same rhythm’, duration for duration. This is the lesson of Margaret Bent's influential 2008 article ‘What is Isorhythm?’ By then, the literal sense of the term had already been normal usage in the work of many scholars, including, besides Bent herself, Ernest Sanders and Daniel Leech-Wilkinson. As a designation of genre, however, ‘the isorhythmic motet’, a looser and vastly more inclusive usage was still generally accepted, and Bent's call for strict consistency between the nominal and adjectival forms of the term effectively limits its application as a generic designation to a small and incohesive assemblage of works, leaving the category without historical relevance. As compensation for a focused reinterpretation of this and many other terms, Bent offers a new terminological precision capable of distinguishing procedures that had been wrongly grouped together in earlier analyses (an example is the sphere of possibilities that had been subsumed under the term ‘diminution’), thereby celebrating a newly revealed diversity of compositional procedures that had not been sufficiently appreciated previously.

Friedrich Ludwig, who coined the term in the early twentieth century, pursued a more general goal: to write a synthetic account of a period of music history. The discovery of the Ivrea codex (Iv) in 1921, which added a number of new motets to the repertory, allowed Ludwig's student Heinrich Besseler to flesh out a detailed narrative. For Besseler, the style of motet pioneered by Philippe de Vitry was an innovation that not only swept away the enormous diversity of late thirteenth-century motet types in France, but also, in its essentials, remained dominant for well over one hundred years, from c. 1316 up to the late motets of Guillaume Du Fay in the 1440s. This broader narrative recedes in Bent's sharpened critical perspective, despite the probability that Philippe de Vitry would have recognized Du Fay's Nuper rosarum flores as a motet. In my revised account, Vitry still figures as the key player, though the point of departure for this episode in music history depends more on literary factors than musical ones.