This thesis examines John Scotus Eriugena’s reading of Augustine’s De musica. It argues that material from Augustine’s text is presented within a nexus of musical, logical, and numerical traditions and that it contributes to those traditions. Eriugena was a careful and imaginative reader of Augustine’s text. His development of the ideas that he drew from this text always remains rooted in musica, but it point far beyond Augustine’s own immediate concerns.

A first part examines the material circumstances of Augustine’s De musica in the early middle ages through the manuscripts themselves as well as ninth- and tenth-century library catalogues. Moreover, it argues that Eriugena knew a glossed copy of the text, which may still survive in Tours. It further posits that Eriugena developed his idea of the uita generalis from glosses on Augustine’s text, though he used it in the first instance to explain parts of Plato’s Timaeus.

A second part concerns the definition of musica in the first book of the Periphyseon. Two versions of the definition are found in the earliest copies of this text. One is written in an Irish hand now believed to be the autograph of Eriugena himself, and the other, a revision of the first, by an Irish scribe with a close and longstanding connection to Eriugena, who is known after his hand as i2. This part of the thesis examines the material and intellectual context of the two definitions and the different relations here negotiated between the musical and logical traditions.

Finally, a third part argues that Augustine’s De musica made a specific and important contribution to Eriugena’s metaphysics of number. Augustine’s text is the principal source for Eriugena’s writing about number. In particular Eriugena develops an account of number framed by Augustine’s narrative of the double motion of number into memory. The changes made to this narrative better to assimilate it within his own metaphysical outlook again reveal Eriugena to be a careful and imaginative reader of Augustine’s text. The thesis demonstrates a rich and productive relation between musica and other philosophical traditions in the ninth century.