This thesis examines the depiction of interspecies transformation, that is, the transformation of living beings between species of animal including human, in medieval Irish literature. It spans texts written from the seventh to the fourteenth centuries, using the wide temporal range, along with an investigation of a number of genres, to consider the many ways in which transformation appears in these texts, and how it functions as a thematic phenomenon. This thesis uses as a primary theoretical lens the work of Gilles Deleuze and Féliz Guattari in their work A Thousand Plateaus, which theorises about non-linear methods of relation. This framework works alongside writing from eco-critical theorists like Donna Haraway and trans theorists like Eva Hayward. The thesis develops an expansive approach to the depiction of transformation, considering not only the individual who transforms, at the moment of their change, but relationships between species more broadly, and transformation as a process that begins before, and extends past, the instant of change.

The first chapter of the thesis considers the corpus of transformation in medieval Irish literature as a whole, looking broadly at how transformation occurs, what species appear in narratives of transformation, and anxieties surrounding cannibalism, domestication, and other aspects in the relationship between human and animal. This chapter also establishes the thesis’s theoretical framework.

Examination of medieval Irish texts featuring transformation between species reveals that transformation is inflected by genre, and occurs in vastly different forms and circumstances dependent on the type of text in which it appears. The thesis thus continues by unfolding its argument over a number of different generic categories. Chapters 2 and 3 consider a body of texts which tell the stories of individuals whose transformations between species grant them supernatural longevity, in turn allowing them to impart their life stories to saints in a Christian narrative present. The second chapter focusses exclusively on the figure Fintan mac Bóchra, an individual who appears in a number of texts as a source of authority on the history and landscape of Ireland, but only sometimes as a creature who transforms between species. Chapter 3 examines a number of other figures whose transformations are associated with their great age and knowledge. It considers knowledge transfer as well as the emotional resonances of these creatures, particularly emotions between the transforming individuals and those of other species. These creatures include the otter who accompanies the part-fish figure Lí Bán, and the multiply-transforming Tuán mac Cairill’s relationships with other members of each species into which he transforms.

Chapter 4 focusses on hagiographic texts, concluding that within this genre, transformation is almost exclusively punitive, unlike the texts in Chapter 3, in which transformation can sometimes be positive. This fourth chapter also considers transformation as isolation, both from human society and from a Christian afterlife. Chapter 5 examines Dindshenchas Érenn, a group of texts which focus on the names and histories of the places of Ireland. Within these texts, transformation almost always leads to death, and has less of the explicitly religious context of the texts appearing in chapters 2–4. Finally, the thesis concludes that transformation becomes visible in these texts through feeling, both emotional and sensory. Emotions often trigger the transformation, as well as extending through it into the transformed creature’s new body. Furthermore, the thesis examines transformation as a vehicle of knowledge, in which change between species allows for the gathering of particular kinds of knowledge and their transfer back into the pool of human, Christian information about Irish history and landscape.