This dissertation addresses the question of how and why artful prose and narrative verse developed so rapidly in late fourteenth-century England, by showing that Boethius' Consolation of Philosophy, long acknowledged as a central thematic source for poetry and prose, played a crucial formal role in the development of both. Boethius' work is a prosimetrum, programmatically alternating philosophical prose with lyrical meter. My dissertation demonstrates that Boethius devises this form to embody his complex theory of literary learning, in which prose and meter rectify a narrator's and reader's understanding and correct his will by a twin process of dialogic argumentation (in the prose sections) and sensual pleasure (in the meters). Prosimetrum is the aesthetic correlative of philosophy's consolation; it is what makes the work a protrepsis, designed to stage the learning process of its narrator. Boethius' practice and theory of prosimetrum as the formal vehicle for narratorial learning made him indispensable to early English authors, including Geoffrey Chaucer, Thomas Usk, Thomas Hoccleve, and Julian of Norwich, and laid the groundwork for literary writing in both prose and meter.