Since the realization, at the beginning of this century, that
the treatise Speculum musicae had been incorrectly attributed to Jehan des Murs by its first
editor, Edmond de Coussemaker, the actual author of this voluminous work of music theory from the
early fourteenth century has remained a shadowy figure. The most certain detail of the author's
identity is his name, contained within an acrostic spelled out over the initials that begin each of
the seven books of the treatise, rendering the given name IACOBUS. The provenances of the three
surviving manuscript sources, all dating from approximately a century after the proposed date of
Speculum musicae, suggest an Italian bias to the transmission of the work, but, as physical
documents, the manuscripts have yet to yield any clues to the author's origins. The treatise
itself is a bit more helpful. Besides offering the author's name, clues within the text have
allowed for the formulation of the following hypothesis concerning the career of Jacobus: that he was
probably born in the diocese of Liège, that he was a student in Paris in the late thirteenth
century, and that he returned to Liège to complete the final books of his treatise, Books 6 and
7 of Speculum musicae. In what follows, I will first briefly evaluate the evidence previously
marshalled to support this hypothesis, and I will then discuss new information pertinent to the
biography of the author.