Internal history

We have already seen that RP is the descendant of the Mercian and West Saxon dialects of Old English, while Scots has Old Northumbrian as its ancestor. These southern and northern dialects of Old English developed into Southern and Northern Middle English. In the early Middle English of approximately 1250 ad, the Northern and Southern vowel inventories were markedly similar; a possible common early Middle English system is given in (4.7). Johnston (1997a: 64) gives a similar system for Older Scots, in terms of source vowels for particular lexical sets in the sense of Wells (1982).

Between the thirteenth and the seventeenth century, a plethora of sound changes affected this common system. Some applied equally in the North and the South, while others affected the systems of the two areas differently, or were restricted to one area. Details of the changes for Scots can be found in Jones (1997b), Johnston (1997a) and McMahon (1989); I shall give details of only two changes, Middle English Open Syllable Lengthening and the Scottish Vowel Length Rule, with some discussion of the Great Vowel Shift where it is relevant to SVLR.