Kernewek Kemmyn was developed, mainly by Ken George, from Unified Cornish in 1986. It takes much of its inspiration from medieval sources, particularly Cornish passion plays, as well as Breton and to a lesser extent Welsh. It was subsequently adopted by the Cornish Language Board as their preferred system. It retained a Middle Cornish base but made the spelling more systematic by applying phonemic orthographic theory, and for the first time set out clear rules relating spelling to pronunciation. Before the Standard Written Form was introduced in 2008, users of KK[who?] claimed that the orthography had been taken up enthusiastically by the majority of Cornish speakers and learners, and advocates[who?] of this orthography claimed that it was especially welcomed by teachers. This assumption was confirmed in 2008, when a survey indicated that KK users made up more than half of all Cornish speakers  After KK's introduction, many Cornish speakers chose to continue using Unified Cornish, and many moved to Revived Late Cornish.
The orthography has drawn heavy criticism from some areas. Since the publication of the Gerlyver Kernewek Kemmyn (dictionary), several writers have condemned the new orthography (Penglase 1994; Williams 1996; Mills 1999). Some supporters of KK claim that its phonetic spelling makes it easier to teach, and that its reconstructed phonology is grounded in the historic corpus of medieval Cornish literature.
Notably several writers have criticised George's reconstructed phonology, claiming it to be academically unsound. In 1994, Charles Penglase berated the lack of authenticity in KK resulting out of George's purely conjectural reconstruction of Middle Cornish phonology. In 1995, Nicholas Williams listed some 25 ways in which he believes the phonology and spelling of KK to be erroneous. In 1999, Jon Mills attempted to show that George's data contains an unspecified number of inaccuracies, and claims that "the English translation equivalents and neologisms given in the Gerlyver Kernewek Kemmyn entail a contrastive lexicology that is at odds with traditional practice as attested in the historical corpus of Cornish". However several of Mills' purported examples of 'inaccuracies' are themselves inaccurate. Mills claims that George misses several attestations of the <ey> diphthong in the word <seyth> 'seven', none of which are actually spelled with anything close to <ey> in the manuscript spellings and in fact are spelled <vii> (i.e. the Roman numeral 7), hence there is no <ey> diphthong to 'omit'. Penglase is critical of all attempts to base the revival on Middle Cornish, not just Kernewek Kemmyn.
Several academics have also lent support to George's reconstruction. Peter Schrijver, in Studies in British Celtic Historical Phonology (1995), finds George's data to be broadly correct, agrees with his analysis of the Middle Cornish phonemic inventory, and supports the view that the Late British 'New Quantity System' was retained in Middle Cornish (pg. 206), all of which is in contrast to Mills and Williams criticisms. In fact Schrijver's analysis differs from George's only in a few individual words.
Another issue, which has caused controversy is that of Cornish placenames. In many instances, there are multiple, conflicting etymologies and possible meanings, but KK has tended to respell these according to one theory or another. This respelling not only can obscure an alternative origin or meaning, but is not always in line with the practice of other forms of revived Cornish.
While its users claim it to be the largest, and so most successful, variety of Cornish, a survey in 2008  indicated that KK users only make up roughly half of all Cornish speakers. However 73.9% of "competent and frequent" writers of Cornish used KK, and 69.6% of them preferred to use KK. 70.4% of "competent and frequent" readers were found to prefer to read KK. Despite this, it has drawn heavy criticism from some areas, particularly its rival forms, Unified Cornish (Unyes) and Modern Cornish, although the survey found that "competent and frequent" writers of these forms of Cornish made up only 18.3% and 10.4% respectively.
In 1987 Kesva an Taves Kernewek (Cornish Language Board) voted to adopt the Kernewek Kemmyn form of Cornish as its standard.
While the various varieties of revived Cornish have had a rocky relationship with one another, this has had the positive effect of creating a publishing and writing boom in Cornish. All of them have been used in constructing the Cornish language Wikipedia, and also in Gorseth Kernow, the Cornish Gorsedd.
The pronunciation of traditional Cornish is a matter of conjecture, but users of Revived Middle Cornish are more or less agreed about the phonology they use.
This is a table of the phonology of Revived Middle Cornish (RMC) as recommended for the pronunciation of Kernewek Kemmyn orthography, using symbols from the International Phonetic Alphabet (IPA).
These are tables of the phonology of Revived Middle Cornish as recommended for the pronunciation of Kernewek Kemmyn, using symbols from the International Phonetic Alphabet (IPA).
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The vowels with their corresponding letters in the Kernewek Kemmyn orthography and the short/long pairs are as follows:
|a ~ a:||? ~ ?:||oe:||i:||? ~ ?:||? ~ o:||u:||y:||? ~ ?:|
1. A vowel is considered short when it comes before double consonants (e.g. ?nn?, ?mm?, and so on), or before any two consonants.
2. Some vowels have a tendency to be reduced to schwas [?] in unstressed syllables