Bilabial consonants are speech sounds produced by bringing the two lips together. They belong to the broader class of labial sounds and are a common place of articulation cross-linguistically. In phonetic terms, bilabials are a subset of consonants and are characterized by lip contact or near-contact that shapes the airstream to create distinct manners of articulation such as stops, nasals, fricatives and trills.

Articulatory characteristics

To make a bilabial sound a speaker uses both the upper and lower lip. The lips may form a complete closure (as in a stop), a narrow channel (a fricative), or a rapid opening and closing (a trill). Nasal bilabials lower the velum to allow air to pass through the nose while the lips form a closure. Acoustic properties depend on the degree and place of labial contact as well as voicing.

Common types and examples

  • Plosives (stops): voiceless [p] and voiced [b], as in English pat [pæt] and bat [bæt].
  • Nasals: bilabial nasal [m], as in map [mæp] or man [mæn].
  • Fricatives: voiceless [ɸ] and voiced [β], which are less common but occur in a number of languages and as allophones (e.g., some realizations of /f/ or /b/).
  • Trill: bilabial trill [ʙ], a rare sound produced by vibrating the lips.
  • Approximants and labialized sounds: approximant gestures may involve strong lip rounding; the labiovelar approximant [w] involves both lip rounding and a velar constriction and is not a pure bilabial.

Distribution and linguistic importance

Bilabial consonants are widespread; simple sets such as /p, b, m/ appear in many unrelated languages. Some bilabial fricatives and the bilabial trill are relatively uncommon and tend to be phonetic or regional variants. Bilabials are often among the earliest consonants acquired by children because they are easy to see and produce, which also makes them prominent in language development and speech therapy.

Distinctions and notable facts

Bilabial sounds differ from labiodental sounds (made with the lower lip and upper teeth, like [f] and [v]) and from labiovelar sounds (involving both lips and a velar constriction, like [w]). In many languages some bilabial symbols may represent allophonic variation rather than separate phonemes; for example, consonants realized between vowels can surface as fricatives or approximants. For reference on the standard symbols used by phoneticians see the IPA.