This thesis focuses on the historical development of dialectal variation in the Gaelic languages with special reference to Irish. As a point of departure, competing scholarly theories concerning the historical relationships between Goidelic dialects are laid out. Next, these theories are tested using dialectometric methods of linguistic analysis. Dialectometry clearly suggests the Irish of Ulster is the most linguistically distinctive of Irish dialects. This perspective on the modern dialects is utilised in subsequent chapters to clarify our understanding of the history of Gaelic dialectal variation, especially during the Old Irish period (AD 600–900). Theoretical and methodological frameworks that have been used in the study of the historical dialectology of Gaelic are next outlined. It is argued that these frameworks may not be the most appropriate for investigating dialectal variation during the Old Irish period. For the first time, principles from historical sociolinguistics are here applied in investigating the language of the Old Irish period. In particular, the social and institutional structures which supported the stability of Old Irish as a text language during the 8th and 9th centuries are scrutinised from this perspective. The role of the ecclesiastical and political centre of Armagh as the principal and central actor in the relevant network structures is highlighted. Focus then shifts to the processes through which ‘standard’ languages emerge, with special reference to Old Irish. The evidence of a small number of texts upon which modern understandings of Old Irish was based is assessed; it is argued that these texts most likely emerged from monasteries in the northeast of Ireland and the southwest of Scotland. Secondly, the processes through which the standard of the Old Irish period is likely to have come about are investigated. It is concluded that the standard language of the period arose primarily through the agency of monastic schools in the northeast of Ireland, particularly Armagh and Bangor. It is argued that this fact, and the subsequent prominence of Armagh as a stable and supremely prestigious centre of learning throughout the period, offers a sociolinguistically robust explanation for the apparent lack of dialectal variation in the language. Finally, the socio-political situation of the Old Irish period is discussed. Models of new-dialect formation are applied to historical evidence, and combined with later linguistic evidence, in an attempt to enunciate dialectal divisions which may have existed during the period.

This project investigates the cognitive linguistic categories that structure the Old Irish landscape lexicon. The semantics of basic landscape vocabulary are differentiated based on collocate analysis and close reading of relevant text passages. Terms are compared across subdomains in order to identify linguistic categories that apply to the overall landscape lexicon. The analysis shows distinctions of (a) domesticated vs. wild landscape features, and (b) landmarks vs. non-landmarks. These distinctions are motivated by a combination of the interactional properties (a, b) and the independent salience (b) of the landscape features. Understanding the cognitive linguistic categories of Old Irish landscape vocabulary provides insight into how medieval Irish society conceptualized the natural world.

This dissertation contains a critical edition of the early Irish tale Aided Derbforgaill “the violent death of Derbforgaill”. It includes an introduction discussing the main thematic components of the tale as well as intertextuality, transmission and manuscript relationship. The edition is accompanied by transcripts from the three manuscript copies of the tale and textual notes. Aided Derbforgaill is an Ulster Cycle tale and belongs to a category of tales describing the death of prominent heroes, rarely heroines, in early Irish literature. Arriving in the shape of a bird to mate with the greatest of all heroes, Cú Chulainn, Derbforgaill is refused by Cú Chulainn on account of him having sucked her blood. Forced to enter a urination competition between women, and upon winning this, Derbforgaill is mutilated by the other competitors. The tale ends with two poems lamenting the death of Derbforgaill. This very short tale is complex, not only in its subject matter, but in the elliptical language of the poetry. Thematically the tale is a combination of very common motifs found elsewhere in early Irish literature, such as the Otherworld, metamorphosis and the love of someone unseen, and some rare motifs that are almost unique to this tale, such as blood sucking and the urination competition. The text also have clear sexual overtones.

This thesis examines the ideal of the Anglo-Saxon and Irish ciuitas, c. 500-1050, by considering what Anglo-Saxon and Irish ecclesiastics understood a ciuitas to be, how they used the term in their own writings and what terms were its vernacular equivalent. When looking at early Insular history, there can be no doubt that the locations that were called ciuitates by Anglo-Saxon and Irish ecclesiastics are some of the most important sites in forming a better understanding of the time period. Ciuitates like Armagh, Canterbury, Clonmacnoise, Iona, Kildare, London and Winchester were settlements that attracted large numbers of people, as well as being centres of both secular and religious power. These ecclesiastical centres had a diversity of individuals within their boundaries, from the ecclesiastics of the sacred centre to monastic tenants and various types of visitors. The importance of Anglo-Saxon and Irish ciuitates cannot only be seen in the frequency of the term's use in primary sources, but also in the great extent to which these sites are mentioned in secondary sources on the time period. Although these communities are often used by scholars to prove or disprove different points of history, the term ciuitas has not been examined in a study devoted to the subject. This thesis has been divided into three chapters. Chapter one considers biblical inspiration in the ideal of the ciuitas, chapter two analyzes the Anglo-Saxon ciuitas and word usage, while chapter three reviews the Irish ciuitas and word use. By the end of this study it will become clear what Anglo-Saxon and Irish ecclesiastics thought a ciuitas to be, as well as the different definitions they understood to apply to these sites.