This essay argues that late medieval manuscript producers were both aware of and at times troubled by the ontological ambiguity of the medium in which they worked. Nelson Goodman’s aesthetic philosophy provides an apt framework for characterizing this ambiguity, which rests on the manuscript’s dual status as both an allograph and an autograph. Embodying features of both, the manuscript demands a third category, which I term the “ambigraph.” Through an examination of manuscripts of Hoccleve’s Regiment of Princes, I demonstrate how both scribes and illuminators struggled with a self-referential text that presents itself as both an original document and the performance of a script. When called upon by the text they copied to produce pictorial evidence of Chaucer’s likeness, scribes and illuminators left behind evidence in both word and image of their perturbation at this brief, as well as their reluctance and refusal to fulfill it. These exertions, I argue, offer a practical theorization of a premodern media concept in lieu of such a theorization in words.