VOWEL QUALITY. A term in phonetics for the property that makes one VOWEL sound different from another: for example, /iː/ as in sheep from /ɪ/ as in ship. The quality of a vowel is determined by the position of the tongue, lips, and lower jaw, and the resulting size and shape of the mouth and pharynx. Vowels are classed as close or open (in British terminology) and high and low (in American terminology) according to whether the tongue is held close to the roof of the mouth or low in the mouth. They are classed as front or back in both terminologies according to whether the body of the tongue is pushed forward or pulled back. They are classed as rounded or spread according to the shape of the lips: for example, the /iː/ in sheep is a close front spread vowel, the /ɪ/ in ship a semihigh front unrounded vowel.

Cardinal vowels

While this general classification provides an approximate description of vowel quality, it is not sufficient to define all the vowels in a system such as English. Some vowels can only be defined in relation to other vowels: for example, /ɛ/ in bet is intermediate between close /ɪ/ in bit and open /æ/ in bat. The most widespread method of dealing with relative vowel quality is based on the system of cardinal vowels devised by Daniel JONES. These vowels are used as reference qualities for the vowels of all languages.

Cardinal [i] is produced with the body of the tongue held forward in the mouth, and with the tongue surface as close as possible to the palate without generating turbulence (which would turn it into a consonant). Cardinal [ɑ] is produced with the body of the tongue held back in the mouth, and with the root of the tongue as close as possible to the back wall of the pharynx, again without generating turbulence. The remaining cardinal vowels are placed at equidistant points on the lines from [i] to [ɑ]. The system of cardinal vowels provides a means of describing vowel sounds.

Cardinal [i] has spread lips; from [i] to [ɑ] the vowels become less spread and progressively more lip neutral. From [ɑ] to [u] they are progressively more rounded, and [u] is fully rounded. For ease of reference, the cardinal vowels are numbered anti-clockwise (counter-clockwise) from 1 to 8. The statement ‘a vowel in the region of cardinal 2’ is equivalent to ‘a vowel in the region of [e]’. Both refer to a ‘half-close front spread vowel’. Most vowels in most languages combine lip spreading with frontness, and rounding with backness, as in the primary cardinal vowels, but this is not always the case. Secondary cardinal vowels have the lip positions reversed from those of the primary cardinals, the first five being rounded and the last three spread. These cardinal vowels are numbered anti-clockwise from 9 to 16.