standardized spelling system. By early Middle English, all unstressed vowels were spelt , probably representing . Also in late Old English, final unstressed became ; during the Middle English period, this final was dropped when it was part of an inflectional syllable (but remained when part of the root, e.g. seven, or in derivational endings, e.g. written). Around Chaucer's time, final was dropped; judging from inflectional evidence, this occurred first when the following word began with a vowel. A century or so later, unstressed also dropped in the plural and genitive ending -es (spelled -s in Modern English) and the past ending -ed. These changes steadily effaced most inflectional endings, e.g.: OE > ME > LME > NE meet OE > ME > LME > NE week OE > ME > LME > NE name In the last two examples, the stressed vowel was affected by open-syllable lengthening. Vocalization of and development of new diphthongs The sound , which had been a post-vocalic allophone of , became vocalized to . This occurred around the year 1200. A new set of diphthongs developed from combinations of vowel+ (either from or from pre-existing ) or vowel+ (from pre-existing ), and also due to borrowing from French – see Diphthongs above. Breaking During the 12th or 13th century, a vowel was inserted between a front vowel and a following (pronounced in this context), and a vowel was inserted between a back vowel and a following (pronounced in this context). Short was treated as a back vowel in this process (the long equivalent did not occur in the relevant context). See H-loss, below. Open-syllable lengthening Around the 13th century, short vowels were lengthened in an open syllable (i.e. when followed by a single consonant that in turn is followed by another vowel). In addition, non-low vowels were lowered: > , > , > , > . This accounts, for example, for the vowel difference between staff and the alternative plural staves (Middle English staf vs. stāves, with open-syllable lengthening in the latter word). This process was restricted in the following ways: It did not occur when two or more syllables followed, due to the opposing process of trisyllabic laxing. It only occasionally applied to the high vowels and , e.g. OE wudu > ME > wood; OE wicu > ME > week. Most instances of and remained as such, e.g. OE hnutu > NE