Labial consonants are consonants in which one or both lips are the active articulator. This generally precludes linguolabials, in which the tip of the tongue contacts the posterior side of the upper lip, making them coronals, but sometimes they behave as labial consonants. The two common labial articulations are bilabials, articulated using both lips, and labiodentals, articulated with the lower lip against the upper teeth, both of which are present in English. The other labial articulation is dentolabials, articulated with the upper lip against the lower teeth (the reverse of labiodental), normally only found in pathological speech.
The most common distribution between bilabials and labiodentals is the English one, in which the stops, [m], [p], and [b], are bilabial and the fricatives, [f], and [v], are labiodental. Bilabial fricatives and the bilabial approximant do not exist in English, but do occur in many languages. For example, the Spanish consonant spelt b or v is pronounced as a voiced bilabial approximant between vowels.
Lip rounding, or labialization, is a common approximant-like co-articulatory feature. English /w/ is a voiced labialized velar approximant, which is far more common than the purely labial approximant [β̞]. In the languages of the Caucasus labialized dorsals like /kʷ/ and /qʷ/ are very common.
Very few languages, however, make a distinction purely between bilabials and labiodentals, making "labial" usually a sufficient specification of a language's phonemes. One language that does make such a distinction is Ewe, having both kinds of fricatives, though the labiodentals are produced with greater articulatory force.
Lack of labials
While most languages make use of purely labial phonemes, a few generally lack them. Examples are Tlingit, Eyak (both Na-Dené), Wichita (Caddoan), and the Iroquoian languages except Cherokee. All of these languages have seen labials introduced under the influence of English.
Many of these languages are transcribed with /w/ and with labialized consonants. However, it's not always clear to what extent the lips are involved in such sounds. In the Iroquoian languages, for example, /w/ involved little apparent rounding of the lips. See Tillamook language for an example of a languages with "rounded" consonants and vowels that do not have any actual labialization.
- McDorman, Richard E. (1999). Labial Instability in Sound Change: Explanations for the Loss of /p/. Chicago: Organizational Knowledge Press. ISBN 0-967-25370-5.