Click consonant

Clicks are stops produced with two articulatory closures in the oral cavity. The pocket of air enclosed between the two closures is rarefied by a sucking action of the tongue. The release of the more forward closure produces what in many cases are the loudest consonants in the language, although in some languages such as Hadza, clicks are more subtle and may even be mistaken for ejective stops. Clicks appear more stop-like or more affricate-like depending on their place of articulation: Clicks involving an apical alveolar or laminal postalveolar closure are acoustically abrupt and sharp like plain stops, while bilabial, dental and lateral clicks have a longer and acoustically noisier sounds that are more like affricates.

Distribution
Clicks occur in all the Khoisan languages of southern Africa, and in several neighbouring Bantu languages, such as Nguni (Zulu, Xhosa, Swazi, Ndebele), Yeyi, and Sesotho, which borrowed them from Khoisan languages. Clicks also occur in Sandawe and Hadza, two languages of Tanzania traditionally classified as Khoisan, as well as in Dahalo, an endangered South Cushitic language of Kenya.

The Southern African Khoisan languages only permit root-initial clicks. Hadza, Sandawe, and several of the Bantu languages also allow syllable-initial clicks within roots, but in no language does a click close a syllable or end a word.

The only non-African language known to employ clicks as regular speech sounds is Damin, a secret ritual code used by speakers of Lardil in Australia. One of the clicks in Damin is actually an egressive click, using the tongue to compress the air in the mouth for an outward (egressive) "spurt". English and many other languages may use clicks in interjections, such as "tsk-tsk" or "gee-up".

Types of clicks
As noted above, clicks necessarily involve two closures: an anterior one which is represented by the special click symbol in the IPA, and a posterior one which is usually velar but can also be uvular. This posterior articulation may be oral or nasal, voiced or voiceless, etc. (It's quite easy to pronounce a nasal click once you realise that while maintaining the double oral closure you're free to breathe through the nose.) Since the posterior articulation is most commonly velar (and can only be velar in most languages), only the place of the anterior articulation (called the release or influx) is normally mentioned, while only the manner of the posterior articulation (called the accompaniment or efflux) is specified. Thus a "nasal dental click" means a click with a dental anterior articulation/release and a velar-nasal posterior articulation/accompaniment.

There are numerous combinations of elements making up a click accompaniment, some of them quite daunting. These include voiceless, voiced, aspirate, breathy voiced, nasal, voiceless nasal, breathy voiced nasal, glottalized, voiceless nasal glottalized, affricate, ejective affricate, prevoiced, prenasalized, and others as well, including extremely complicated combinations such as a voiced velar click followed by voiceless affricated ejective,, and a velar ejective click followed by uvular ejective, (Ladefoged and Maddieson, 1996). This means that pentagraphs like gk!x’ are possible in a practical orthography. However, many of these combinations are consonant clusters rather than separate phonemes.

The size of click inventories ranges from as few as four for the Dahalo language of Kenya, to dozens in the Northern and Southern Khoisan languages, and up to 83 clicks (including 50 simple clicks) in !Xóõ (Ladefoged and Maddieson, 1996). In the latter language, over 70% of words begin with a click.

Transcription
The five click releases with dedicated symbols in the International Phonetic Alphabet (IPA) are bilabial, dental , palato-alveolar or "palatal" , (post)alveolar or "retroflex" , and alveolar lateral. The retroflex and palatal releases are "abrupt"; that is, they are sharp popping sounds with little frication (turbulent airflow). The bilabial, dental, and lateral releases, on the other hand, are "noisy": they are longer, lip- or tooth-sucking sounds with turbulent airflow, and are sometimes called affricates. (They can, however, still have either affricate or non-affricate accompaniments.) The apical releases, and, are sometimes called "grave", because their pitch is dominated by low frequencies; while the laminal releases,  and , are sometimes called "acute", because they are dominated by high frequencies. Thus the alveolar sounds something like a cork pulled from a bottle (a low pitched pop), at least in Xhosa; while the dental  is like English ''tsk! tsk!'', a high pitched sucking on the incisors. The lateral clicks are pronounced by sucking on the molars of one or both sides. The bilabial is different than what many people associate with a kiss: the lips are pressed more-or-less flat together, as they are for a [p] or an [m], not rounded as they are for a [w].

The IPA came up with a set of Latin-based symbols for these sounds, but they were never much used, and were eventually given up for the Khoisanist symbols.

There are a few less well attested releases, such as a noisy laminal denti-alveolar lateral release (Ⅲ [triple pipe] in an ad hoc transcription), which contrasts with an apical postalveolar lateral in Mangetti Dune !Kung; an abrupt sub-apical retroflex release <‼> in Angolan !Kung; and a "slapped" alveolar click in Hadza and Sandawe, where the tongue slaps the bottom of the mouth after the release. (These distinctions may suffice for the Damin releases as well.) However, the Khoisan languages are poorly attested, and it is quite possible that, as they become better described, more click releases will be found.

Technically, when a full click consonant (that is, an accompaniment plus release) is transcribed, a tie bar should be used, because the accompaniment overlaps the release in time. (For example, in a nasal click such as, the nasal is pronounced before, during, and after the release .) However, a tie bar is not often used in practice, and when the accompaniment is a simple [k], it will sometimes be omitted as well. That is, =  =  =  =.

The accompaniment is generally written first: or. However, many Khoisanists prefer to write the accompaniment second: or. This is because the diacritics which follow the click symbols belong to the accompaniment rather than the release. A prime example of this are the ejective clicks, as. Here it is the uvular that is ejective, not the palatal click release, and the IPA convention of writing  is misleading. Regardless, elements which do not overlap with the release are always written accordingly: The prenasalization is always written first in =, and the second ejective is always written afterwards in  =.

While the SAMPA encoding for IPA into ASCII doesn't have symbols for transcribing clicks, the proposed X-SAMPA standard does:  O\, |\, |\|\, =\, and !. Some instead suggest ||\, #\ or "\ for the alveolar lateral click. The Kirshenbaum system uses a different method: clicks are denoted by digraphs, with the click symbol (always "!") added to the stop homorganic to the release, but with the manner of the accompaniment. For example, /t!/ is a voiceless dental click, and /m!/ is a nasal bilabial click. (This transcription is used in the literature on Damin.) However, the International Phonetic Association recommends using the IPA symbols in Unicode, or using the number codes which they have assigned to each symbol.

Accompaniments
(Data is primarily from Ladefoged; see references at individual language articles.)

There is a great variety of click accompaniments, though it is a matter of debate how many of them are simple consonants and how many consonant clusters. With so few click languages, and so little study of them, it is also unclear to what extent clicks in different languages may be equivalent to each other.

Some Khoisan languages are typologically unusual in allowing mixed voicing in non-click consonant clusters, such as, so it's not unexpected that they would allow mixed voicing in clicks as well, and this can be taken as evidence that these clicks are also clusters.

There is ongoing discussion as to which other clicks are best analysed as consonant clusters, as in several cases this is not obvious. For example, some linguists feel that ejective clicks are not possible, and that those described as such are most likely clusters. Indeed, in many languages this appears to be the case. However, in others phonetic measurements have found that, while the ejective release follows the click release, it is the accomplaniment closure that is ejective, not a subsequent consonant. (In Ladefoged's analysis in the table below, if there is only a single segment, this is indicated by a single non-subscript letter for the accompaniment.)

Of the languages illustrated below, !Xóõ is Southern Khoisan, Nama, Korana, and Gǀui are Central Khoisan, Zhuǀ’hõasi is Northern Khoisan, and ‡Hoan is unclassified. These languages are spoken primarily in Namibia and Botswana. (See List of Khoisan languages for classification.) Xhosa is a Bantu language of South Africa; Dahalo is a Cushitic language of Kenya; Hadza and Sandawe are spoken in Tanzania; and Damin was an initiation jargon in northern Australia.

The four Dahalo accompaniments occur only with a dental release. Damin has only a nasal accompaniment with its normal clicks, but in addition has a voiceless unaspirated release for its egressive "click".

For clarity, the full accompaniment is written after the release, and the tie bar is omitted.

Inventories of click releases
There are seven known click releases, not counting slapped or egressive clicks. These are bilabial affricated, or "bilabial"; laminal denti-alveolar affricated , or "dental"; apical (post)alveolar plosive , or "alveolar"; laminal postalveolar (palato-alveolar) plosive , or "palatal"; subapical postalveolar (retroflex) (rare); and two lateral clicks, which in the only language known to distinguish them are laminal denti-alveolar lateral  and apical postalveolar lateral. No language is known to have more than five of these.

Names found in the literature
The oldest terms for the click releases, such as in Bleek 1911, are closer to modern terminology than much of what was published in between. Here are the terms used in some of the main references.

Click loss
We do not know how clicks first arose, and the development of clicks from other consonants has never been observed, but it seems likely that they arose from consonant clusters of some type.

However, several still vibrant languages demonstrate click loss. For example, the East Tshu-Khwe languages have lost a large percentage of their clicks, presumably due to Bantu influence. Generally a click is replaced by a consonant that retains the manner of articulation of the accompaniment. Alveolar click releases tend to simply drop out, leaving a velar stop or affricate such as, while palatal clicks  leave behind a palatal stop such as , or a post-alveolar affricate , and dental clicks  tend to leave an alveolar affricate  behind. That is, in the latter cases the resulting consonant retains the manner of the accompaniment but the place of the release.

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