of possible vowel sounds. Some languages have also constructed additional vowel letters by modifying the standard Latin vowels in other ways, such as æ or ø that are found in some of the Scandinavian languages. The International Phonetic Alphabet has a set of 28 symbols representing the range of essential vowel qualities, and a further set of diacritics to denote variations from the basic vowel. The writing systems used for some languages, such as the Hebrew alphabet and the Arabic alphabet, do not ordinarily mark all the vowels, since they are frequently unnecessary in identifying a word. Technically, these are called abjads rather than alphabets. Although it is possible to construct English sentences that can be understood without written vowels (cn y rd ths?), single words in English lacking written vowels can be indistinguishable; consider dd, which could be any of dad, dada, dado, dead, deed, did, died, diode, dodo, dud, dude, odd, add, and aided. (Note that abjads generally express some word-internal vowels and all word-initial and word-final vowels, whereby the ambiguity will be much reduced.) The Masoretes devised a vowel notation system for Hebrew Jewish scripture that is still widely used, as well as the trope symbols used for its cantillation; both are part of oral tradition and still the basis for many bible translations—Jewish and Christian. Shifts The differences in pronunciation of vowel letters between English and its related languages can be accounted for by the Great Vowel Shift. After printing was introduced to England, and therefore after spelling was more or less standardized, a series of dramatic changes in the pronunciation of the vowel phonemes occurred, and continued into recent centuries, but were not reflected in the spelling system. This has led to numerous inconsistencies in the spelling of English vowel sounds and the pronunciation of English vowel letters (and to the mispronunciation of foreign words and names by speakers of English). Audio samples Systems The importance of vowels in distinguishing one word from another varies from language to language. Nearly all languages have at least three phonemic vowels, usually as in Classical Arabic and Inuktitut, though Adyghe and many Sepik languages have a vertical vowel system of . Very few languages have fewer, though some Arrernte, Circassian, and Ndu languages have been argued to have just two, and , with being epenthetic. It is not straightforward to say which language has the most vowels, since