De legitimis ordinibus pentachordorum et tetrachordorum by Theinred of Dover has long been known to scholars but has virtually remained inaccessible until recent years: a transcription of its text, made by John L. Snyder, was mounted onto TML only in 1996, and a critical edition by Snyder published in 2006 detailed an argument that dated the treatise to c. 1150. This seminar brings together three perspectives for repositioning Theinred in the fourteenth century, a date that had been offered in the very earliest accounts of the theorist. Responding to the 12th-century hypothesis, Hamilton will argue for a fourteenth-century date based on a new evaluation of Theinred’s sources; Lefferts will present contexts for—and close readings of—Theinred’s text that draw him into a tight circle of prominent theorists of the same era, and Witkowska-Zaremba will consider Theinred’s theories in the context of Boethius’s De institutione musica, pointing to the ideas and solutions presented by Boethius in the fourth book of his treatise and their reception in England around 1300.