Through an analysis of the competing theories that emerged in the early fourteenth century on how best to notate music’s shortest notes—semibreves and minims—chapter 4 investigates whether the innovations of the ars nova merely tweaked at the edges of the previous ars antiqua system and offered nothing substantially new, or whether they represent a moment of real discontinuity in the theory and practice of music. In a close reading of book 7 of Speculum musicae, and the evidence set forth by the Vitriacan Ars nova witnesses and Des Murs, I pin down exactly which teachings of the ars nova formed the basis of Jacobus’s critique of the moderns’s notation of short notes, and analyse which fourteenth-century motets exemplify these ars nova practices. The results of this analysis offer support for the contention that the ars nova critiqued by Jacobus probably dates somewhat later than current musicological narratives have tended to place it, and that many of the motets that current musicological scholarship classify as ars nova motets, at the time might not have been considered as being written in the new style.