This dissertation treats the controversial Syrian poet Abū l-ʿAlāʾ al-Maʿarrī (d. AD 1058) as a case study of medieval Arabic authorship. On one hand, readers have traditionally attributed to authors like al-Maʿarrī a stable position whereby their writings transparently reflect their life and thought. On the other hand, recent scholarship on manuscript culture considers medieval authorship as unstable and diffuse, in contrast to the writerly unity of print culture. Left unreconciled, these competing views perpetuate misconceptions, such as that al-Maʿarrī must either be a sincere believer or a devious doubter. In my assessment, neither end of this spectrum is satisfactory. Therefore I draw those ends closer together by examining the paratexts — titles, prefaces, glosses, and other writings attached by an author to his own works — of al-Maʿarrī, which are part of a lifelong effort to curate his own legacy. I focus on three paratexts from Luzūm mā lā yalzam (Self-Imposed Necessity), al-Maʿarrī’s poetry collection notorious for its critiques of religion: an introduction, a self-commentary, an exchange of letters. This choice of texts is deliberate, since it in response to reader doubts that al-Maʿarrī must consolidate his authorship. I use insights from functional linguistics, such as that language is a social practice; its use represents agency exercised within constraints; and that language users negotiate personal and social conceptions of identity. Through this analysis, I gain purchase over al-Maʿarrī’s rhetorical stance encoded by his paratexts. That stance is best described by Robert R. Edwards’ term “counter-authorship,” namely a position of authority against authority. Through explicit formulation and implicit performance, al-Maʿarrī resists literary and religious orthodoxy wedded to political power by setting out an ethics of writing, commanding the physical margins of texts, and forcing dialectical engagement by readers. To show historical continuity, I also include a chapter on modern receptions of al-Maʿarrī’s authorship. This demonstrates the persistence of his image as a counter-authority, albeit in another time and with different stakes. These findings mediate between the two opposing views of medieval authorship described above. On the one hand, they reveal how authorship and textuality can be stabilized through mechanisms like paratexts, while on the other, they complicate authorship as biographism by heeding questions of rhetoric, audience, and convention. The results of my study also show the importance polemical discourse, namely the anticipation of and response to reader doubt; and of textuality, namely the physical, documentary form of the text itself. That these both join in the process of negotiating authorship as much as the text’s very language becomes clear in a case like that of al-Maʿarrī.