Major changes occurred in the English vowel system between about 1400 and about 1750. English spelling began to stabilise before most of those changes took place. As a result, English spelling does not match well with current pronunciation, as many native and non-native learners have discovered to their cost. This post summarises one group of those changes, often known as the Great Vowel Shift.
Basic phonetics
Vowels can be classified by height—by how high the tongue is. They can also be classified by whether the tongue is at the front of the mouth (front vowels), near the centre of the mouth (centre vowels) or near the back of the mouth (back vowels).
Vowels can be short or long.
Great Vowel Shift
The Great Vowel Shift affected only long vowels. Although many changes occurred in short vowels as well, this post does not discuss those changes.
In summary, the Great Vowel Shift raised all long vowels: it converted vowels into higher vowels. For example, the low-mid vowel /ɔ:/ was replaced by the high-mid vowel /o:/.
The diagram below summarises the changes, using characters from the International Phonetic Alphabet:
- the low central or front long vowel /a:/ raised to become the low-mid long vowel /ɛ:/
- the low-mid front vowel /ɛ:/ raised to become the high-mid long vowel /e:/
- the high-mid long vowel /e:/ raised to become the high long vowel /i:/
- the high long vowel /i:/ couldn’t be raised any further. It become the diphthong /ai:/ A diphthong is a sequence of a vowel and a semi-vowel.
- the mid low back vowel /ɔ:/ raised to become the high-mid back vowel /o:/
- the high-mid back vowel /o:/ raised to become the high back vowel /u:/
- the high back vowel /u:/ couldn’t be raised any further. It become the diphthong /au:/ For example, mouse was previously pronounced [mu:s], much like modern moose. After the Shift, it was pronounced [maus].
| Sound | Description | Example |
| a: | low central | like modern bath |
| ɛ: | low-mid front | like modern bet |
| e: | high-mid front | like modern bake |
| i: | high front | like modern geese |
| ɔ: | low-mid back | like modern bought |
| o: | high-mid back | like modern bone |
| u: | high back | like modern goose |
| ai: | diphthong | like modern mice |
| au: | diphthong | like modern mouse |
The colon (:) indicates that a vowel is long.
The modern equivalents given above are only very rough guides. For example, many of the modern long vowels shown are diphthongs, not pure vowels.
The modern equivalents reflect pronunciation in standard Southern British English.
Diagram of the shift
For simplicity and clarity, the following diagram presents an overview of the final effect of the Great Vowel Shift. In reality, this did not happen overnight and it did not happen all at once. The Great Vowel Shift was in fact a series of several separate changes over perhaps 3 to 4 centuries.
based on diagrams in various textbooks, originating in Jespersen (1909)
English spelling
English spelling started to become standardised before the Great Vowel Shift was complete. As a result, as Minkova (2014) notes, English is the only European language using the Roman alphabet in which the the vowel letters <a, e, i, o> refer to sounds [ei, i:, ai, ou] that differ significantly from the sounds that those letters refer to in Latin or, for example, German, Spanish and Hungarian.
Sources
A Historical Phonology of English, Donka Minkova (2014)
A Modern English Historical Grammar on Historical Principles: Part 1, Sounds and Spellings, Otto Jespersen (1909)