Phonological history of the high back vowels

Most dialects of modern English have two high back vowels: the near-close near-back rounded vowel /ʊ/ found in words like foot, and the close back rounded vowel /uː/ (realized as central [ʉː] in many dialects) found in words like goose. This article discusses the history of these vowels in various dialects of English, focusing in particular on phonemic splits and mergers involving these sounds.

In the Old English vowel system, there was a pair of short and long high back vowels, /u/ and /uː/, both written ⟨u⟩ (the longer vowel is often distinguished as ⟨ū⟩ in modern editions of Old English texts). There was also a pair of back vowels of mid-height, /o/ and /oː/, written ⟨o⟩ (the longer one often ⟨ō⟩ in modern editions).

The same four vowels existed in the Middle English system. The short vowels were still spelt ⟨u⟩ and ⟨o⟩, but long /uː/ came to be spelt as ⟨ou⟩, and /oː/ as ⟨oo⟩. Generally the Middle English vowels descended from the corresponding Old English ones, although there were certain alternative developments – see Phonological history of Old English#Changes leading up to Middle and Modern English.

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