Why do written English vowels differ from other Latin-based orthographies?

Question

Written English vowels differ from other Latin-based orthographies. Consider what the written vowels in the romance languages represent. Also, for example, consider this simple comparision between a few German and English vowels:

 German    English
-------------------
 a = [a]   a = [e]
 e = [e]   e = [i]
 i = [i]   i = [aj]

Has this always been so? Is the pattern regular? When and why did the shift occur?

Answer 1

Starting in the 1400s, English vowels began a change known as the Great Vowel Shift, resulting in the change from English vowels being pronounced similarly to how the German vowels are pronounced now to how English vowels are pronounced today.

The diagram in that article explains the shift much more clearly and completely than I could, but the gist of it is this:

(Using the International Phonetic Alphabet):

• The vowel of time changed from [iː] to [aɪ].
• The vowel of see changed from [eː] to [iː].
• The vowel of east changed from [ɛː] and merged with the vowel see to become ultimately [iː].
• The vowel of name changed from [aː] to [eɪ].
• The vowel of day changed from [æj] and merged with the vowel of name to become ultimately [eɪ].
• The vowel of house changed from [uː] to [aʊ].
• The vowel of moon changed from [oː] to [uː].
• The vowel of stone changed from [ɔː] to [oʊ].
• the vowel of know changed from [au] and merged with the vowel of stone to become [oʊ].
• the vowel of law changed from [ɑu] to [ɔː]
• the vowel of new changed from [eu]/[iu] to [juː]
• the vowel of dew changed from [ɛu] and merged with the vowel of new to become [juː]
• the vowel of that changed from [a] to [æ]
• the vowel of fox changed from [o] to [ɒ]
• the vowel of cut changed from [ʊ] to [ʌ]

"Vowel spaces", that is, the system of vowels in a language and how they are arranged, are sensitive to changes in complex ways. When one vowel changes in how it is pronounced, due to normal language change, often several other vowels change at the same time, to keep the arrangement of the vowels in the vowel space "equally spaced". Such groups of changes are known as chain shifts. Keeping vowels evenly distributed in the vowel space avoids confusion as to which vowel was produced.

Answer 2

Other interesting references on the Great Vowel Shift:

• See and Hear the GVS (excellent visual and audio!)
• Brief History of English
• More English History

The Great Vowel Shift would probably be just an historical curiosity if it weren't for the fact that the first printing press opened in London in 1476, right in the middle of the shift!

Before the printing press was invented, the words in handwritten texts had been spelled according to the dialect of the scribe who wrote them. However, book production was slow and few people could read in any case.
The early printers used the older spellings which Middle English scribes had used. They didn't understand the significance of the pronunciation changes that had just gotten well underway.
By the time the vowel shift was complete (about 100 years from start to finish), hundreds of books had been printed with the older spellings.
The new high volume of book production combined with increasing literacy proved to be powerful forces against spelling change.
As a consequence, many spellings have become "fixed" to the Middle English pronunciation, rather than the modern ones, and we still spell the word for the earth's satellite as "moon."