Classification of vowels Vowels are classified in terms of: 1. the height of the bulk of the tongue in the mouth 2. the front/back position of the tongue in the mouth 3. the degree of lip-rounding 4. the length of vowels Number of vowels There are 20 vowels: 12 single vowels (or monothongs) and 8 double vowels (or diphthongs). Monothongs /ˈm{n{H{Nz/ Front Central Back High Low Middle Close Half-close Half-open Open                  ['vaUl tS¿:t] Front Central Back High Low Middle Close Half-close Half-open Open • heed • hid • head • had • cut • hard • hot • saw • shoe • put • the • bird ['vaUl tS¿:t]  :  :  