Approximants are speech sounds (phones) that could be regarded as intermediate between vowels and "typical" consonants. In the articulation of approximants, articulatory organs produce a narrowing of the vocal tract, but leave enough space for air to flow without much audible turbulence. Approximants are therefore more open than fricatives. This class of sounds includes lateral approximants like , as in lip, and approximants like and in yes and well which correspond closely to vowels and semivowels.
Some approximants resemble vowels. The term semivowel is often used for such segments. (Semivowels are non-syllabic vowel-like segments. While some phoneticians restrict the term to true non-syllabic vowels, which form diphthongs, others include the subset of approximants that resemble vowels. The difference phonetically is that these approximants are closer than the corresponding non-syllabic vowels.)
In articulation and often diachronically, palatal approximants correspond to front vowels, velar approximants to back vowels, and labialized approximants to rounded vowels. In American English, the rhotic approximant corresponds to the rhotic vowel.
|Approximant||Corresponding vowel||Place of articulation|
When emphasized, approximants may be slightly fricated (that is, the airstream may become slightly turbulent), which is reminiscent of fricatives. Examples are the y of English yes! (especially when lengthened) and the "weak" allophones of Spanish b, d, g, which are often transcribed as fricatives (often due perhaps to a lack of dedicated approximant symbols). However, such frication is generally slight and intermittent, unlike the strong turbulence of fricative consonants.
This confusion is also common with voiceless approximants, which necessarily have a certain amount of fricative-like noise. For example, the voiceless labialized velar approximant has traditionally been called a fricative, and no language is known to contrast it with a voiceless labialized velar fricative . Tibetan has a voiceless lateral approximant, , and Welsh has a voiceless lateral fricative , but the distinction is not always clear from descriptions of these languages. Again, no language is known to contrast the two.
For places of articulation further back in the mouth, languages do not contrast voiced fricatives and approximants. Therefore the IPA allows the symbols for the voiced fricatives to double for the central approximants, with or without a lowering diacritic.
Occasionally the glottal "fricatives" are called approximants, since [h] typically has no more frication than voiceless approximants, but they are often phonations of the glottis without any accompanying manner or place of articulation.
In lateral approximants, the center of tongue makes solid contact with the roof of the mouth. However, the defining location is the side of the tongue, which only approaches the teeth.
Although many languages have central vowels which lie between back/velar and front/palatal , there are no confirmed reports of corresponding approximants. However, Mapudungun may be a possibility: It has three high vowel sounds, , , , written "i", "u", "ü", and three corresponding consonants, written "y", "w", "q". The first two are clearly and . The "q" is often described as a voiced unrounded velar fricative, but some texts note a correspondence between "q" and that is parallel to - and -. An example is liq "white".