Tongue Positions
The changes in the position of the tongue determine largely the shape of the mouth and pharyngeal cavities. The tongue may move forward and backward, up and down, thus changing the quality of vowel sounds.
(1) When the tongue moves forward and backward various parts of it may be raised in the direction of the palate.
When the tongue is in the front part of the mouth and the front part of it is raised to the hard palate a front vowel is pronounced. This is the position for the English vowels [i:, e, æ].
When the tongue is in the front part of the mouth but slightly retracted, and the part of the tongue nearer to centre than to front is raised, a front-retracted vowel is pronounced. Such is the position for the English vowel [i].
When the front of the tongue is raised towards the back part of the hard palate the vowel is called central. This is the position for the English vowels [ʌ, ɜ:, ə].
When the tongue is in the back part of the mouth and the, back of it is raised towards the soft palate a back vowel is pronounced. This is the position for the English vowels [ɑ:, ɐ, ɔ:, u:].
When the tongue is in the back part of the mouth but is slightly advanced and the central part of it is raised towards the front part of the soft palate a back-advanced vowel is pronounced. This is the position for the English vowel [ʊ].
(2) Moving up and down in the mouth various parts of the tongue may be raised to different height towards the roof of the mouth.
When the front or the back of the tongue is raised high towards the palate the vowel is called close (high). This is the way the English vowels [i:, i, ʊ, u:].
When the front or the back of the tongue is as low as possible in the mouth open (low) vowels are pronounced. This is the way to pronounce the English vowels [æ, ɑ:, ɐ, ɔ:].
When the highest part of the tongue occupies the position intermediate between the close and the open one mid vowels are pronounced. This is the position for the English vowels [e, ʌ, з:, ə].
Lip Position.
The shape of the mouth cavity is also largely dependent on the position of the lips. When the lips are neutral or spread the vowels are termed unrounded.
When the lips are drawn together so that the opening between them is more or less round the vowel is called rounded. This is the position for the English vowels [ɐ, ɔ:, ʊ, u:].