An IMPROPER DIPHTHONG or DIGRAPH is merely a collection of two vowels in the same syllable, of which only one is sounded; as in rain, teach.
The diphthongs in the following words are all that are in common use, viz.: toil, toy, sound, cow, peal, oil, audible, awning, say, seine, people, feud, obey, eschew, believe, loan, hoe, hue, juice. Of these oi, oy, ou, and ow are the only proper diphthongs.
A TRIPHTHONG is produced by running together three vowel sounds in the same syllable.
A triphthong is PROPER if all three of the vowels are sounded. (But there are no proper triphthongs that I know of.)
A triphthong is IMPROPER or is called a TRIGRAPH if one or two of the three vowels is silent; as in adieu, beauty.
[Fourth Month.]
CONSONANTS.
Consonants are divided on three different bases; as follows:
I. Mutes and SEMIVOWELS.
The mutes represent an explosive sound, and are so called because the mouth organs are closed just before the sound is uttered and the voice is momentarily mute.
The four subvocals b, d, j, g, and their cognates, p, t, ch, and k, are generally classed as mutes. Pronounce them and see if they do not represent explosive sounds.