The vowels are represented by five letters and twenty phonemes divided into seven short vowels, for example /e/ and /ʌ/, five long vowels, for example /u:/ and /a: /, and eight diphthongs /ɪə/ and /ʊə/. Vowels are sounds produced by the complete passage of air through the vocal tract, without complete closure or stenosis. Unlike consonants, all vowel phonemes are voiced. When dividing words into syllables, each syllable must contain a vowel and is called the syllable nucleus. Like consonants, vowel phonemes are described based on the height and position of the tongue in the mouth and the shape of the lips. First, the height of the tongue in the mouth is divided into: high position as in the acute word /i:/, central position as in the girdle word /ɜː/, and low position as in the cart word /a:/. Secondly, the position of the tongue in the mouth is divided into: anterior position as in the word sheep /i:/, central position as in the word girl /ɜː/ and posterior position as in the word pool /u:/. Third, lip positions are recognized as rounded as in the word horse /ɔː/ and not rounded as in the word ship