The rise of phonemic vowel quantity in Cornish. Evidence and implications. Part I: Vowel quantity in stressed monosyllables; long vowels and heavy diphthongs in Middle Cornish

abstract: This paper traces the history of vowel quantity in Cornish, beginning with the New Quantity System, a set of phonological rules established in the sixth century ce that governed vowel and consonant length in Cornish, Welsh, and Breton. Under the New Quantity System, consonants were phonemically long or short and the length of every vowel was allophonically determined by the number and nature of any consonants that followed it and by its position relative to the principal stress accent of the word containing it. However, by the first half of the fifteenth century, vowel length had become phonemic in Cornish, and its short, half-long, and long vowel phonemes had begun to develop in divergent ways, with short vowels laxing and centralizing, half-long vowels tensing, and fully long vowels extending and, in some cases, breaking to heavy diphthongs. Part I of this study assesses orthographic evidence for the rise of phonemic vowel quantity in stressed monosyllables and traces related phonological developments among Cornish vowels and diphthongs from the fourteenth through the eighteenth centuries. Particular attention is paid to examining the influence of English orthography and phonology on Middle and Late Cornish scribal practice, as well as to documenting the phonological similarities and differences between Cornish, Breton, and Welsh in the late medieval and modern eras, as vowel quantity achieved phonemic status in all three Brythonic languages during this period. This analysis will form the basis for a new proposed chronology of phonological change in Cornish, which will be presented in Part II.