Thesis advisor: Michael J. Connolly / The Insular Celtic languages, such as Irish and Welsh, distinctively feature a morphophonemic process known as initial consonant mutation. Essentially the initial sound of a word changes due to certain grammatical contexts. Thus the word for 'car' may appear as carr, charr and gcarr in Irish and as car, gar, char and nghar in Welsh. Originally these mutations result from assimilatory phonological processes which have become grammaticalized and can convey morphological, semantic and syntactic information. This paper looks at the primary mutations in Irish and Welsh, showing the phonological changes involved and exemplifying their basic triggers with forms from the modern languages. Then it explores various topics related to initial consonant mutations including their historical development and impact on the grammatical structure of the Celtic languages. This examination helps to clarify the existence and operations of the initial mutations and displays how small sound changes can have a profound impact upon a language over time. / Thesis (BA) — Boston College, 2008. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Slavic and Eastern Languages. / Discipline: College Honors Program.

This thesis produces a definition of consonant mutations, a hitherto relatively unexplored phenomenon in typology, using a sample of languages from the Celtic and Uralic languages. It is defined using Canonical Typology. The base of the phenomenon is established as ‘functionalized consonant alternations’, with seven dimensions of variation: conditioning elements>no conditioning elements; sole functional indicator>accompanied by other morphemes; more than two grades>two grades; some effect on surrounding vowels>only affecting the consonant; only leniting>also non-leniting sound changes; word-initial/-final>word-medial placement; and less regular>more regular. It is also argued that mutations’ phonology is less important than their function.