The thesis entitled "Irish English modal verbs from the fourteenth to the twentieth cen-turies" submitted by Marije van Hattum at The University of Manchester for the degree of Doctor of Philosophy on June 11th 2012 provides a corpus-based study of the development of Irish English modal verbs from the fourteenth to the twentieth centuries in comparison to mainland English. More precisely, it explores the morpho-syntax of CAN, MAY, MUST, SHALL and WILL and the semantics of BE ABLE TO, CAN, MAY and MUST in the two varieties. The data of my study focuses on the Kildare poems, i.e. fourteenth-century Irish English religious poetry, and a self-compiled corpus consisting of personal letters, largely emigrant letters, and trial proceedings from the late seventeenth to the twentieth centuries.The analysis of the fourteenth and nineteenth centuries is further compared to a similar corpus of English English. The findings are discussed in the light of processes associated with contact-induced language change, new-dialect formation and supraregionalization. Contact-induced language change in general, and new-dialect formation in particular, can account for the findings of the fourteenth century. The semantics of the Irish English modal verbs in this century were mainly conservative in comparison to English English. The Irish English morpho-syntax showed an amalgam of features from different dialects of Middle English in addition to some forms which seem to be unique to Irish English. The Irish English poems recorded a high number of variants per function in comparison to a selection of English English religious poems, which does not conform to predictions based on the model of new-dialect formation. I suggest that this might be due to the fact that the English language had not been standardized by the time it was introduced to Ireland, and thus the need to reduce the number of variants was not as great as it is suggested to be in the post-standardization scenarios on which the model is based.In seventeenth- and eighteenth-century Ireland, increased Irish/English bilingualism caused the formation of a second-language (L2) variety of English. In the nineteenth century the bilingual speakers massively abandoned the Irish language and integrated into the English-speaking community. As a result, the varieties of English as spoken by the bilingual speakers and as spoken by the monolingual English speakers blended and formed a new variety altogether. The use of modal verbs in this new variety of Irish English shows signs of colonial lag (e.g. in the development of a deontic possibility meaning for CAN). Additionally, the subtle differences between BE ABLE TO and CAN in participant-internal possibility contexts and between epistemic MAY and MIGHT in present time contexts were not fully acquired by the L2 speakers, which resulted in a higher variability between the variants in the new variety of Irish English. In the late nineteenth and early twentieth centuries the use of modal verbs converged on the patterns found in English English, either as a result of linguistic accommodation in the case of informants who had migrated to countries such as Australia and the United States, or as a result of supraregionalization in the case of those who remained in Ireland.