depending on surrounding vowels. New diphthongs formed from vowels followed by or (including from former ). Length distinctions were eliminated in these diphthongs, yielding diphthongs plus borrowed from French. Middle English breaking: Diphthongs also formed by the insertion of a glide or (after back and front vowels, respectively) preceding . Mergers of new diphthongs: Early on, high-mid diphthongs were raised: merged with (hence eye < OE ēġe rhymes with rye < *riġe < OE ryġe), merged with and merged with (hence rue < OE hrēoƿan rhymes with hue < OE hīƿ and new < OE nīƿe). In Late Middle English, and merge as , so that vain and vein are homophones (the vein–vain merger). Trisyllabic laxing: Shortening of stressed vowels when two syllables followed. This results in pronunciation variants in Modern English such as divine vs divinity and south vs. southern (OE sūðerne). Middle English open syllable lengthening: Vowels were usually lengthened in open syllables (13th century), except when trisyllabic laxing would apply. Reduction and loss of unstressed vowels: Remaining unstressed vowels merged into . Starting around 1400 AD, is lost in final syllables. Initial clusters , , were reduced by loss of . Voiced fricatives became independent phonemes through borrowing and other sound changes. before back vowel becomes ; becomes . Modern English sword, answer, lamb. in swore is due to analogy with swear. The cluster, present in words imported from Norman, is deaffricated, and merges with (which had perhaps been apical in medieval times, as in closely related Dutch and Low German), thus merging sell and cell. But unlike French, and are fully preserved. Up to Shakespeare's English This period is estimated to be c. AD 1400–1600. H-loss completed: (written gh) lost in most dialects, so that e.g. taught and taut become homophones, likewise bow (meaning "bend") and bough. and when not followed by a vowel undergo mutations: Before , a coronal consonant or word-finally, they are diphthongized to and . (By later changes, they become and , as in modern salt, tall, bolt, roll.) After this, the combinations and lose their in most accents, affecting words like talk, caulk, and folk. Words acquired after this change (such as talc) were not affected. Before , the becomes silent, so that half and calf are pronounced with , and salve and halve are pronounced with . is exempt, so that solve keeps its . is not wholly exempt, as