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Lot–cloth split


The phonology of the low back vowels of the English language has undergone changes both overall and with regional variations, through Old and Middle English to the present. The sounds heard in modern English were significantly influenced by the Great Vowel Shift, as well as more recent developments such as the cot–caught merger.

In the Old English vowel system, the vowels in the low back area were unrounded: /ɑ/, /ɑː/. There were also rounded back vowels of mid-height: /o/, /oː/. The corresponding spellings were ⟨a⟩ and ⟨o⟩, with the length distinctions not normally marked; in modern editions of Old English texts, the long vowels are often written ⟨ā⟩, ⟨ō⟩.

As the Old English (OE) system developed into that of Middle English (ME), the OE /ɑ/ merged with the fronted /æ/ to become a more central ME /a/. Meanwhile, OE /ɑː/ was rounded and raised to ME /ɔː/. OE /o/ remained relatively unchanged, becoming a short ME vowel regarded as /o/ or /ɔ/, while OE /oː/ became ME /oː/ (a higher vowel than /ɔː/). Alternative developments were also possible; see English historical vowel correspondences for details.


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