This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
In uttering true vowel-sounds the soft palate is raised so as to cut off the air in the nose, which then does not take part in the resonance. For some other sounds (the semivowels or resonants) the initial step is, as in the case of the true vowels, the production of a laryngeal tone; but the soft palate is not raised, and the mouth-exit is more or less closed by the lips or the tongue; hence the blast partly issues through the nose, and the air there takes part in the vibrations and gives them a special character; this is the case with m, n, and ng.
Consonants are sounds produced not mainly by the vocal cords, but by modifications of the expiratory blast on its way through the mouth. The current may be interrupted and the sound changed by the lips (labials, as p and b); or, at or near the teeth, by the tip of the tongue (dentals, as t and d); or, in the throat, by the root of the tongue and the soft palate (gutturals, as k and g).
Consonants may also be classified by the kind of movement which gives rise to them. In explosives an interruption to the air-current is suddenly interposed or removed (p, b, t, d, k, g). Other consonants are continuous (f, s, r) and may be divided into (1) aspirates, when the air is made to rush through a narrow aperture, as, for example, between the lips (f) or the teeth (s) or the tongue and the palate (sh) or the tongue and the teeth (th); (2) re8onant8 or semivowels; (3) vibratories, the different forms of r, due to vibrations of parts bounding a constriction put in the way of the air-current on its passage.
Is the long i of English a true vowel ?
What is meant by the semivowels ?
What are consonants ? How may they be classified ?