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Fricatives are consonants produced by forcing air through a narrow channel made by placing two articulators close together. These may be the lower lip against the upper teeth, in the case of [f]; the back of the tongue against the soft palate, in the case of German [x] (the final consonant of Bach); or the side of the tongue against the molars, in the case of Welsh [ɬ] (appearing twice in the name Llanelli). This turbulent airflow is called frication. A particular subset of fricatives are the sibilants. When forming a sibilant, one still is forcing air through a narrow channel, but in addition, the tongue is curled lengthwise to direct the air over the edge of the teeth. English [s], [z], [ʃ], and [ʒ] are examples of sibilants.
The usage of two other terms is less standardized: "Spirant" can be a synonym of "fricative", or (as in e.g. Uralic linguistics) refer to non-sibilant fricatives only. "Strident" could mean just "sibilant", but some authors include also labiodental and uvular fricatives in the class.
- [s] voiceless coronal sibilant, as in English sip
- [z] voiced coronal sibilant, as in English zip
- [s̪] voiceless dental sibilant
- [z̪] voiced dental sibilant
- [s̺] voiceless apical sibilant
- [z̺] voiced apical sibilant
- [s̠] voiceless postalveolar sibilant (laminal)
- [z̠] voiced postalveolar sibilant (laminal)
- [ʃ] voiceless palato-alveolar sibilant (domed, partially palatalized), as in English ship
- [ʒ] voiced palato-alveolar sibilant (domed, partially palatalized), as the s in English vision
- [ɕ] voiceless alveolo-palatal sibilant (laminal, palatalized)
- [ʑ] voiced alveolo-palatal sibilant (laminal, palatalized)
- [ʂ] voiceless retroflex sibilant (apical or subapical)
- [ʐ] voiced retroflex sibilant (apical or subapical)
All sibilants are coronal, but may be dental, alveolar, postalveolar, or palatal (retroflex) within that range. However, at the postalveolar place of articulation, the tongue may take several shapes: domed, laminal, or apical, and each of these is given a separate symbol and a separate name. Prototypical retroflexes are subapical and palatal, but they are usually written with the same symbol as the apical postalveolars. The alveolars and dentals may also be either apical or laminal, but this difference is indicated with diacritics rather than with separate symbols.
Central non-sibilant fricatives
- [ɸ] voiceless bilabial fricative
- [β] voiced bilabial fricative
- [f] voiceless labiodental fricative, as in English fine
- [v] voiced labiodental fricative, as in English vine
- [θ̼] voiceless linguolabial fricative
- [ð̼] voiced linguolabial fricative
- [θ], [θ̟] voiceless dental non-sibilant fricative, as in English thing
- [ð], [ð̟] voiced dental non-sibilant fricative, as in English that
- [θ̠], [ɹ̝̊] voiceless alveolar non-sibilant fricative
- [ð̠], [ɹ̝] voiced alveolar non-sibilant fricative
- [r̝̊] voiceless trilled fricative
- [r̝] voiced trilled fricative
- [ç] voiceless palatal fricative
- [ʝ] voiced palatal fricative
- [x] voiceless velar fricative
- [ɣ] voiced velar fricative
- [ɧ] voiceless palatal-velar fricative (articulation disputed)
- [χ] voiceless uvular fricative
- [ħ] voiceless pharyngeal fricative
The IPA also has letters for epiglottal fricatives,
with allophonic trilling, but these might be better analyzed as pharyngeal trills. 
- [ɬ̪] voiceless dental lateral fricative
- [ɮ̪] voiced dental lateral fricative
- [ɬ] voiceless alveolar lateral fricative
- [ɮ] voiced alveolar lateral fricative
- [ɬ̠] voiceless postalveolar lateral fricative (Mehri)
- [ɭ̥˔] or [ꞎ] voiceless retroflex lateral fricative
- [ʎ̥˔] or [ʎ̝̊] voiceless palatal lateral fricative (also written ⟨⟩)
- [ʟ̝̊] voiceless velar lateral fricative (also written ⟨⟩)
- [ʟ̝] voiced velar lateral fricative
The lateral fricative occurs as the ll of Welsh, as in Lloyd, Llewelyn, and Machynlleth ([maˈxənɬɛθ], a town), as the unvoiced 'hl' and voiced 'dl' or 'dhl' in the several languages of Southern Africa (such as Xhosa and Zulu), and in Mongolian.
IPA letters used for both fricatives and approximants
No language distinguishes voiced fricatives from approximants at these places, so the same symbol is used for both. For the pharyngeal, approximants are more numerous than fricatives. A fricative realization may be specified by adding the uptack to the letters, [ʁ̝, ʕ̝]. Likewise, the downtack may be added to specify an approximant realization, [ʁ̞, ʕ̞].
(The bilabial approximant and dental approximant do not have dedicated symbols either and are transcribed in a similar fashion: [β̞, ð̞]. However, the base letters are understood to specifically refer to the fricatives.)
In many languages, such as English, the glottal "fricatives" are unaccompanied phonation states of the glottis, without any accompanying manner, fricative or otherwise. However, in languages such as Arabic, they are true fricatives.
In addition, [ʍ] is usually called a "voiceless labial-velar fricative", but it is actually an approximant. True doubly articulated fricatives may not occur in any language; but see voiceless palatal-velar fricative for a putative (and rather controversial) example.
Fricatives are very commonly voiced, though cross-linguistically voiced fricatives are not nearly as common as tenuis ("plain") fricatives. Other phonations are common in languages that have those phonations in their stop consonants. However, phonemically aspirated fricatives are rare. [sʰ] contrasts with [s] in Korean; aspirated fricatives are also found in a few Sino-Tibetan languages, in some Oto-Manguean languages, and in the Siouan language Ofo (/sʰ/ and /fʰ/). The record may be Cone Tibetan, which has four contrastive aspirated fricatives: /sʰ/ /ɕʰ/, /ʂʰ/, and /xʰ/.
Phonemically nasalized fricatives are rare. Some South Arabian languages have /z̃/, Umbundu has /ṽ/, and Kwangali and Souletin Basque have /h̃/. In Coatzospan Mixtec, [β̃, ð̃, s̃, ʃ̃] appear allophonically before a nasal vowel, and in Igbo nasality is a feature of the syllable; when /f v s z ʃ ʒ/ occur in nasal syllables they are themselves nasalized.
|central non-sibilant||ɸ β||f v
|θ̼ ð̼||θ̟ ð̟ (θ̪͆ ð̪͆)||θ ð||θ̠ ð̠||θ͇ ð͇ (laminal)
ɹ̝̊ ɹ̝ (apical)
|ɹ̠̊˔ ɹ̠˔||ç ʝ (laminal)
ɻ̝̊ ɻ̝ (apical)
|χ ʁ̝||ħ ʕ̝||h̝
|lateral fricative||ɬ̪ ɮ̪||ɬ ɮ
|ɬ̠ ɮ̠|| ʎ̝ (laminal)
ꞎ ɭ˔ (apical)
|laminal sibilant||s̻̪ z̻̪||s̄ z̄ (s̟ z̟)||s͇ z͇
|s̠ z̠ (s̻̠ z̻̠)
ʃ̻ ʒ̻ (domed)
ŝ ẑ (ʆ ʓ) (closed)
|apical sibilant||s̺̪ z̺̪||s̺ z̺||ṣ ẓ (s̺̠ z̺̠)
|fricative trill||r̝̊ r̝||ʀ̝̊ ʀ̝||ʜ ʢ|
|fricative flap||ɾ̞̊ ɾ̞|
|nasalized fricative||β̃||f̃ ṽ||ð̃||s̃ z̃||ʃ̃ ʒ̃||h̃|
H is not a fricative in English (see /h/).
Until its extinction, Ubykh may have been the language with the most fricatives (29 not including /h/), some of which did not have dedicated symbols or diacritics in the IPA. This number actually outstrips the number of all consonants in English (which has 24 consonants). By contrast, approximately 8.7% of the world's languages have no phonemic fricatives at all. This is a typical feature of Australian Aboriginal languages, where the few fricatives that exist result from changes to plosives or approximants, but also occurs in some indigenous languages of New Guinea and South America that have especially small numbers of consonants. However, whereas [h] is entirely unknown in indigenous Australian languages, most of the other languages without true fricatives do have [h] in their consonant inventory.
Voicing contrasts in fricatives are largely confined to Europe, Africa, and Western Asia. Languages of South and East Asia, such as the Dravidian and Austronesian languages, typically do not have such voiced fricatives as [z] and [v], which are familiar to many European speakers. These voiced fricatives are also relatively rare in indigenous languages of the Americas. Overall, voicing contrasts in fricatives are much rarer than in plosives, being found only in about a third of the world's languages as compared to 60 percent for plosive voicing contrasts.
About 15 percent of the world's languages, however, have unpaired voiced fricatives, i.e. a voiced fricative without a voiceless counterpart. Two-thirds of these, or 10 percent of all languages, have unpaired voiced fricatives but no voicing contrast between any fricative pair.
This phenomenon occurs because voiced fricatives have developed from lenition of plosives or fortition of approximants. This phenomenon of unpaired voiced fricatives is scattered throughout the world, but is confined to nonsibilant fricatives with the exception of a couple of languages that have [ʒ] but lack [ʃ]. (Relatedly, several languages have the voiced affricate [dʒ] but lack [tʃ].) The fricatives that occur most often without a voiceless counterpart are – in order of ratio of unpaired occurrences to total occurrences – [ʝ], [β], [ð], [ʁ] and [ɣ].
Fricatives appear in waveforms as random noise caused by the turbulent airflow, upon which a periodic pattern is overlaid if voiced. Fricatives produced in the front of the mouth tend to have energy concentration at higher frequencies than ones produced in the back. The centre of gravity, the average frequency in a spectrum weighted by the amplitude, may be used to determine the place of articulation of a fricative relative to that of another.
- John Esling (2010) "Phonetic Notation", in Hardcastle, Laver & Gibbon (eds) The Handbook of Phonetic Sciences, 2nd ed., p 695.
- Ladefoged, Peter; Maddieson, Ian (1996). The Sounds of the World's Languages. Oxford: Blackwell. ISBN 0-631-19814-8.
- Guillaume Jacques 2011. A panchronic study of aspirated fricatives, with new evidence from Pumi, Lingua 121.9:1518-1538
- Laver (1994: 255–256) Principles of Phonetics
- There are likely to be more aspirated, murmured and nasal fricatives than shown here. ⟨s̄ ṣ ŝ⟩ are not IPA transcription
- Maddieson, Ian. 2008. "Absence of Common Consonants". In: Haspelmath, Martin & Dryer, Matthew S. & Gil, David & Comrie, Bernard (eds.) The World Atlas of Language Structures Online. Munich: Max Planck Digital Library, chapter 18. Accessed on 2008-09-15.
- Maddieson, Ian. "Voicing in Plosives and Fricatives", in Martin Haspelmath et al. (eds.) The World Atlas of Language Structures, pp. 26–29. Oxford: Oxford University Press, 2005. ISBN 0-19-925591-1.
- Maddieson, Ian. Patterns of Sounds. Cambridge University Press, 1984. ISBN 0-521-26536-3.
- Zsiga, Elizabeth C. (2013). The Sounds of Language: An Introduction to Phonetics and Phonology. Wiley-Blackwell. p. 129. ISBN 978-1-4051-9103-6.
- Johnson, Keith (2012). Acoustic and Auditory Phonetics (3rd ed.). Wiley-Blackwell. pp. 162–3. ISBN 978-1-4051-9466-2.
- Kiss, Zoltán G. (2013). "Measuring acoustic correlates of voicing in stops and fricatives". In Szigetvári, Péter. VLlxx: Papers Presented to László Varga on His 70th Birthday. Budapest: Department of English Linguistics, Eötvös Loránd University.