Johannes de Muris's Musica speculativa cited by Jacobus de Ispania

It is known that the seventh book of Jacobus's Speculum musicae contains, alongside other quotations from Ars Nova treatises, the earliest extant transmission of the salient passage of Johannes de Muris's Musica speculativa, Conclusio XVIII, where Muris questions the nature of the fourth as a perfect consonance. However, the relevant passages of Musica speculativa cited and discussed by Jacobus have not yet been analysed in the context of the rich manuscript tradition of the Musica speculativa, which served the needs of musical education throughout Latin Europe for at least two hundred years. In order to position Jacobus's citations of Muris within the framework of the Musica speculativa tradition, I examine several significant variant readings contained in Speculum musicae, comparing them to two French, most probably Parisian, manuscripts transmitting versions A (A-SPL Cod. 264/4) and B (BnF lat. 7378A) of Musica speculativa. Both A and B versions are provided with colophons dated 1323 and 1325, respectively. Establishing which version of Musica speculativa was the source of Jacobus's citations provides a new basis for the dating of two other treatises by Muris to which Jacobus refers, namely Notitia artis musicae and Compendium musicae practicae, and, more generally, for the date of the seventh book of Speculum musicae.