Approximants are speech sounds that involve the articulators approaching each other but not narrowly enough, nor with enough articulatory precision,, citing to create turbulent airflow. Therefore, approximants fall between fricatives, which have a degree of constriction tight enough to produce a turbulent airstream, and vowels, which have no constriction. This class includes vowel-like sounds such as and (as in and , respectively), as well as liquids such as and (as in and , respectively), among other consonants with relatively low degrees of stricture. They are a subclass of sonorants and continuants.
Terminology Before Peter Ladefoged coined the term approximant in the 1960s,, citing the terms frictionless continuant and semivowel were used to refer to non-lateral approximants. As a distinctive feature, approximant has also sometimes been expanded to encompass vowels in addition to semivowels (glides) and liquids.
Semivowels
Some approximants resemble vowels in acoustic and articulatory properties and the terms semivowel and glide are often used for these non-syllabic vowel-like segments. The correlation between semivowels and vowels is strong enough that cross-language differences between semivowels correspond with the differences between their related vowels., citing Semivowels may be distinguished from the rest of approximants via a feature of prolongability; while all other approximants are prolongable, semivowels are momentary, as prolonging them results instead in the formation of their vocalic equivalents ( → )., citing
Vowels and their corresponding semivowels alternate in many languages depending on the phonological environment, or for grammatical reasons, as is the case with Indo-European ablaut. Similarly, languages often avoid configurations where a semivowel precedes its corresponding vowel., citing A number of phoneticians distinguish between semivowels and approximants by their location in a syllable. Although he uses the terms interchangeably, remarks that, for example, the final glides of English and differ from French ('through') and ('tub') in that in the French examples, the approximants appear in the syllable coda, whereas in the English ones, they appear in the syllable nucleus. This means that opaque (if not minimal) contrasts can occur in languages like Italian (with the i-like sound of piede 'foot', appearing in the nucleus: , and that of 'plane', appearing in the syllable onset: ) and Spanish (with a near minimal pair being 'abject' and 'opened').
In a related sense, the terms semivowel and semiconsonant are often treated as synonyms in English linguistic tradition, though the latter may be regarded as somewhat antiquated. However, in other linguistic traditions, a distinction is made between the two terms. In these traditions, semivowels refer to non-syllabic vowel offglides (such as ) often found as partial components of syllable nuclei (such as in diphthongs), while semiconsonants refer to consonant onglides (such as ) often found in syllable onsets. An example demonstrating this difference can be observed in the interjections yay and wow .
Coordinate vowels The following table demonstrates vowel correspondences with associated approximants. The § rhotic approximants listed here are not widely considered to be semivowels, but are provided as they do map to corresponding vowels. +Approximant-vowel correspondences Vowel Correspondingapproximant Place of articulation Example Palatal Spanish ('I extend') vs. ('he extended') Labio-palatal French ('sharp') vs. ('needle') Velar Korean ('food') vs. ('doctor') Labio-velar Spanish ('I continue') vs. ('he/she/it continued') and ('you continued') used only in the formal treatment of . Pharyngeal ~ ~ Alveolar ~ Retroflex North American English vs.
Centralized correlates and symbolization Although many languages have central vowels , which lie between back/velar and front/palatal , there are few cases of a corresponding approximant (or equivalently ). One is in the Korean diphthong or , though it is more frequently analyzed as velar (as in the table above), and Mapudungun may be another, with three high vowel sounds, , , and three corresponding consonants, , and , and a third one is often described as a non-labialized voiced velar fricative; some texts note a correspondence between this approximant and that is parallel to – and –. An example is (?) ('white').Listen to a recording
It has been noted that the expected symbols for the approximant correlates of are , , or (as such, the correlate vowels may also be transcribed as ). An additional distinction of roundedness type may also be made between and : the former being compressed, and the latter protruded (the same distinction may be applied to and ). One might also distinguish and by slight degrees of fronting and backing (and by extension, and ), thus being referred to as post-palatal and pre-velar, respectively.
Alternation and glide-formation
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. This can create alternations (as shown in the above table).
In addition to alternations, glides can be inserted to the left or the right of their corresponding vowels when they occur next to a hiatus. For example, in Ukrainian, medial triggers the formation of an inserted that acts as a syllable onset so that when the affix is added to ('football') to make 'football player', it is pronounced , but ('Maoist'), with the same affix, is pronounced with a glide. Dutch for many speakers has a similar process that extends to mid vowels: → ('cinema') + → ('seas') → ('fluorine') + → ('male dogs') → ('Rwanda') → ('Boaz')
Similarly, vowels can be inserted next to their corresponding glide in certain phonetic environments. Sievers' law describes this behaviour for Germanic.
Non-high semivowels also occur. In colloquial Nepali speech, a process of glide-formation occurs, where one of two adjacent vowels becomes non-syllabic; the process includes mid vowels so that ('cause to wish') features a non-syllabic mid vowel. Spanish features a similar process and even nonsyllabic can occur so that ('right away') is pronounced . It is not often clear, however, whether such sequences involve a semivowel (a consonant) or a diphthong (a vowel), and in many cases, it may not be a meaningful distinction.
Contrast with fricatives
According to their standard definitions, approximants (such as ) contrast with fricatives (such as ) in that fricatives produce turbulence, but approximants do not. In addition to less turbulence, approximants also differ from fricatives in the precision required to produce them. When emphasized, approximants may be slightly fricated (that is, the airstream may become slightly turbulent), which is reminiscent of fricatives. However, such frication is generally slight and intermittent, unlike the strong turbulence of fricative consonants.
Spirants Terminology and ambiguity In discussing Spanish, suggested setting up a category of spirant approximants (such as ) contrasting with both semivowel approximants and fricatives, described as "non-rhotic central approximants". The term has since been used with regularity by Martínez-Celdrán and other authors, particularly when discussing the phonetics of Spanish and other Iberian languages such as Galician. revived the term "frictionless continuant" – which historically referred more broadly to non-lateral approximants – to distinguish this same class, and continued to use the term in subsequent works., , ,
However, as notes, both the spirant and frictionless continuant terminologies suffer from some level of ambiguity, as they both recall older (albeit now mostly disused) definitions with subtle differences from their current meaning. Other names that have been used for this class invoke fricatives, with prefix modifiers such as "weak", "approximated", and "lenited". No dominant and preferred term has yet emerged, but for simplicity, this page uses spirant approximants. The class includes all approximants that are both non-liquid (rhotic and lateral) and non-semivowel. They remain distinct from fricatives in having the characteristic non-turbulent (laminar) airflow of approximants.
Examples and related Though spirant approximants are more constricted (having a lower F2 amplitude), longer, and unspecified for rounding ( vs. ), the distributional overlap is limited. Spirant approximants can only appear in syllable onset (including word-initially, where semivowels never appear). The two overlap in distribution after and : () vs. , and although there is dialectal and idiolectal variation, speakers may also exhibit other near-minimal pairs like vs. . One potential minimal pair (depending on dialect) is vs. .
The feature is not present in all dialects of Spanish. Other dialects differ either by merging the two and neutralizing the contrast, or conversely by enhancing the contrast through shifting the fricative to another place of articulation and potentially assibilating (such as , a feature called ), like in Rioplatense Spanish (some dialects of Rioplatense, such as the Buenos Aires dialect, even devoice to , a feature called ).
The syllabic fricatives found in some languages (sometimes referred to as "apical vowels", particularly in Sinological circles, as they behave like vowels phonologically) have also been reported to have similar features to spirant approximants, being approximant-like in their articulation.
Gutturals For places of articulation further back in the mouth, from uvular to epiglottal (which may be grouped under the umbrella term guttural consonants), languages do not contrast voiced fricatives and approximants. Therefore, the assigned symbols in the IPA for the voiced fricatives of these places are typically also used for the approximants, and often without a lowering diacritic.
Occasionally, the glottal "fricatives" are described as approximants, since typically has no more frication than voiceless approximants (described in the section below), but they are often segmental phonations of the glottis without any accompanying manner or place of articulation.
Voicelessness
There has historically been some controversy over whether voiceless approximants can exist. Positions against the phonetic category have included the argument that voiceless airflow is necessarily turbulent and therefore by definition produces a fricative sound, while others have argued that the terminology is somewhat contradictory, as such sounds would be inaudible by definition of approximants (see below). In contrast, more recent research distinguishes between turbulent (fricative-like) and laminar (vowel- or approximant-like) airflow in the vocal tract, with voiced fricatives characterized by more strongly turbulent airflow than voiceless fricatives due to tighter glottal constriction. Ball & Rahilly (1999) state that "the airflow for voiced approximants remains laminar (smooth), and does not become turbulent," while with voiceless approximants airflow is "usually somewhat turbulent"; because of this, the distinction between voiceless approximants and voiceless fricatives is not always clear. As such, voiceless approximants are rarely, if ever, distinguished phonemically from voiceless fricatives in the sound system of a language. discuss the issue and conclude "In practice, it is difficult to distinguish between a voiceless approximant and a voiceless fricative at the same place of articulation [...] there is no evidence that any language in the world makes such a distinction crucial."
Phonetic characteristics