In human speech, a
sound in which the flow of air from the lungs passes through the mouth with minimal obstruction and without audible
friction is called a vowel sound such as the i in “fit,” and the a
in “pack.” Although usually produced with vibrating vocal cords, vowels may be
pronounced without such vibration, resulting in a voiceless, or whispered,
sound. From the viewpoint of articulatory phonetics, vowels are classified
according to the position of the tongue
and lips
and, sometimes, according to whether or not the air is released through the
nose.
According to position of tongue a division of vowels
can be made into front, central, back, close, half-close, half-open and open vowels. According to the shape of lips the vowels
also can be classified as rounded and
unrounded vowels.