It may help you in the study of vowel sounds to know something about how they are grouped or classified by speech experts. Your attention was directed in a previous chapter to the various ways in which the oral cavity could be modified through adjustments of the articulatory organs. Their position is a basis for the phonetician’s arrangement.

Listen to the quality of each vowel and observe with a mirror the shape of your lips as you say successively oo — oh — ah — ay — ee. In careful pronunciation, the lips usually arc rounded into a small circle for oo which becomes larger for oh. For ah the lips are open to their edges or corners. In pronouncing the vowels ay and ee, the corners of the lips move back slightly and the aperture of the mouth narrows. Hence, oo and oh are sometimes called the rounded vowels, and ah, ay, and ce are designated unrounded " vowels.’
Vowels are also classified as front and back sounds, according to the position of the tongue. In forming vowels, such as ee and ay, the front, or blade, of the tongue is raised toward the roof of the mouth. It is higher for ee than for ay. In the vowels, such as oo and oh, the back of the tongue is raised. It is higher for oo than for oh. For ah, the tongue is relatively flat in the mouth. The sounds in which the front of the tongue is the highest part are called "forward" vowels. Those in which the back of the tongue is the highest are called "back" vowels.

Vowels are also grouped on the basis of color or quality. The front vowels are termed – bright," and the back vowels are called dark " sounds. You may more readily perceive the characteristics of brightness and darkness if you compare sounds heard in familiar words, such as moan, main; tin, ton; team, tomb; bubble, babble; flitter, flutter; ramble, rumble; see, saw. Some people tend to color the voice with one quality of vowel. For instance, the oo quality may be prominent and carry over into all sounds, making the voice monotonous, small, and generally dull. Or ee may be over-used, giving the voice However, in singing, the lips are often said to be neutral. That is, except for slight changes brought about by dropping and raising the jaw, they may remain in practically a constant position for all vowels.

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