it is most extensive in American and (in younger speakers) Canadian English. Northern Cities Vowel Shift in Inland Northern American English: raising and tensing of (in reversal in many locations before non-nasal consonants) fronting of (also somewhat in reversal) lowering of backing and lowering of backing of lowering and backing of Changes to centering diphthongs in non-rhotic varieties of English (England and Australia): smooth to : near, square, start, north. smooths to , breaks to , or lowers and merges with (pour–poor merger): Triphthongs smooth to or (tower–tire, tower–tar and tire–tar mergers). Cot–caught merger: lowering of to in Western American English, some dialects in New England, and dialects scattered in Great Britain. This sound change is still in progress. Examples of sound changes The following table shows a possible sequence of changes for some basic vocabulary items, leading from Proto-Indo-European (PIE) to Modern English. The notation ">!" indicates an unexpected change, whereas the simple notation ">" indicates an expected change. An empty cell means no change at the given stage for the given item. Only sound changes that had an effect on one or more of the vocabulary items are shown. NOTE: Some of the changes listed above as "unexpected" are more predictable than others. For example: Some changes are morphological ones that move a word from a rare declension to a more common one, and hence are not so surprising: e.g. * "three" >! * (adding the common West Germanic feminine ending -u) and "heart" (stem ) >! (change from consonant stem to n-stem). Some changes are assimilations that are unexpected but of a cross-linguistically common type, e.g. "four" >! where ** would be expected by normal sound change. Assimilations involving adjacent numbers are especially common, e.g. "four" >! by assimilation to "five" (in addition, is a cross-linguistically common sound change in general). On the other extreme, the Early Modern English change of "one" >! is almost completely mysterious. Note that the related words alone ( < all + one) and only ( < one + -ly) did not change. Summary of vowel developments Development of Middle English vowels Monophthongs This table describes the main historical developments of English vowels in the last 1000 years, beginning with late Old English and focusing on the Middle English and Modern English changes leading to the current forms. It provides a lot of detail about the changes taking place in the last