2.5 Description of English vowels

　 Vowels are sounds made with the vocal tract more open than it is for consonants. There is hardly any obstruction of the airflow. Vowels are outnumbered by consonants, because the articulators in producing them are fewer. The basic parameters for describing vowels are:

　1) whether the jaw moves and whether the tongue position is changed;

　2) what part of the tongue is raised and how high it is raised;

　3) whether the lips are rounded;

　4) whether the vocal tract is constricted, i.e. whether the muscles are tense.

　 Simple vowels (also called pure vowels or monophthongs) and diphthongs are two major types of vowels. The sound quality is not changed in the former, but changed in the latter. This can be felt in pronouncing flat and flight: the tongue moves from one position to another and the quality of the vowel changes accordingly in pronouncing flight.

　 Diphthongs fall into two categories: centering diphthongs and closing diphthongs. All centering diphthongs end in [], and closing diphthongs in [] or []. In standard British, there are nine diphthongs:[] [] [] [] and [] [] [] [] [].

　 Simple vowels are described in terms of the part of the tongue and the height of the tongue. The tongue is imaginatively cut into three sections: front, central and back. Vowels produced with the front of the tongue raised are called front vowels, such as [] in beat, [] in bit, [] in bet and [] in bat. Central vowels in English are [] (called a schwa) and [], as in the word worker. Back vowels in British English are [] [] [] [] and [], as in words food, foot,, cop, court, and car respectively.

　 Vowels produced with the same part of the tongue are distinguished by the height of the tongue. [] and [] are high front vowels, [] is mid front, and [] is low front. Similarly, [] and [] are mid central, [] is low central; [] and [] are high back, [] and [] are mid back, and [] is low back.

　 Simple vowels are often put into two classes: rounded and unrounded. In British English, all the back vowels except [] are rounded; other simple vowels are unrounded. In Chinese and French, there is a front high rounded vowel. Simple vowels in the so-called received pronunciation of British English can be specified in the following figure:

	Front	Central	Back
High	i: i		u: u
Mid	e
Low

　　Tensity is a quality that can be used to further distinguish vowels of the same position and height. In producing long vowels and diphthongs the vocal tract is constricted, so these vowels are called tense, and others are lax. Now, every simple vowel can be described and distinguished. See the following table for the features of each simple English vowel.