Is modern-day spoken bilingualism any different from historical written bilingualism? Do the same rules and theories apply? When medieval Irish scribes used Latin and Irish in one sentence, what does this tell us about their proficiency, their education, and their audience? In short, what can medieval Irish bilingualism tell us about the society that fostered it?
These are the questions that this thesis attempts to answer through the analyses of the bilingual commentary text that is found together with the ninth-century Irish martyrology Félire Óengusso. It provides a diplomatic edition of the bilingual glosses in manuscript Oxford, Bodleian Library, Rawlinson B505 and discusses the potential function of the Commentary and its origin. This is followed by a grammatical analysis of any code-switches into Irish or Latin that occur according to Pieter Muysken’s typology of code-switching. From this analysis, it becomes clear that code-switching patterns seem to have been influenced by the typological distance between Irish and Latin but also by chronological developments and societal norms regarding language use. From an additional functional analysis, it appears that code-switching in medieval Irish texts may be both a functional communicative device and an unconscious expression of bilingual identity.