According to the place of articulation we distinguish lip[16] stops, point[17] stops, front (palate)[18] stops and back (palate)[19] stops.
22. Lip stops.—When the breath is stopped at the lips, three different sounds may be produced.
1. [p], when there has been no vibration of the vocal chords.
In precise or emphatic speech, sufficient breath escapes after the opening of the passage to give the effect of [h][20]; thus Pay, pay![21] [pͪei, pͪei]. This occurs mostly before accented vowels, and sometimes finally[22]: I hope [ai houpͪ].[23]
[p] is written p or pp; rarely ph (as in a common pronunciation of diphtheria [dipθiːᵊriə], for which see § 27).
Notice the spelling of hiccough [hikʌp].
2. , when there has been vibration of the vocal chords.
is written b or bb.
3. [m], when the velum is lowered and part of the breath passes out through the nose. (Generally speaking, this sound is voiced; but when it is immediately followed by a voiceless sound, it may be partly voiced, then voiceless (phonetic sign: mˑ). Then lamp is strictly [læmmˑp]. We may say: [m] is unvoiced or devocalized before a voiceless stop.) Notice the difference in length of [m] in lamb, hammer, glum, moon; in which of these words is it short?
In comfort, triumph the [m] is often labiodental: the breath is stopped by the upper teeth and lower lip, not by both lips.