Click consonant

A click consonant, or simply click, is a type of non-pulmonic consonant in which a pocket of air trapped between two closures is released, producing a sharp, percussive sound. Unlike most speech sounds, which rely on airflow from the lungs (pulmonic egress), clicks are produced using ingressive velaric airflow, generated by creating a vacuum within the oral cavity. Clicks are a distinctive feature of several language families in Africa, most notably the Khoisan languages, where they form a core part of the phonological system, and are also found in some Bantu languages of Southern Africa, such as Xhosa and Zulu, as well as in the ceremonial language Damin of Australia.

Phonetic Production and Articulation

The production of a click involves two simultaneous closures within the vocal tract, creating a sealed chamber of air. The primary, or anterior, closure is made with the lips or the front of the tongue against the teeth or alveolar ridge. The secondary, or posterior, closure is made further back, typically with the back of the tongue against the velum (soft palate). The body of the tongue is then lowered, often by depressing the center, which expands the enclosed chamber and rarefies the air inside, creating a partial vacuum. The release of the anterior closure allows outside air to rush into the low-pressure area, producing the characteristic clicking sound. The posterior closure is then released separately, often silently, to allow for subsequent speech sounds.

Clicks are classified primarily by the place of the anterior (click) articulation. The five primary click types, defined by the International Phonetic Alphabet (IPA), are:

• Bilabial clicks [ʘ]: The anterior closure is made with both lips. The sound is similar to a loud kiss.
• Dental clicks [ǀ]: The tip of the tongue is placed against the back of the upper teeth. The sound is acoustically sharp, like the English interjection "tsk tsk" (the tut of disapproval).
• (Post)alveolar clicks [ǃ]: The tip or blade of the tongue is placed against the alveolar ridge or the post-alveolar region. This produces a hollow, 'pop'-like sound, reminiscent of a cork being pulled from a bottle.
• Palato-alveolar clicks [ǂ]: The blade of the tongue is placed against the alveolar ridge and palate, often with a broader contact. The release can sound sharper and flatter than the alveolar click.
• Alveolar lateral clicks [ǁ]: The tip of the tongue is placed against the alveolar ridge, and one or both sides of the tongue are lowered for the release. The sound is similar to that used to urge on a horse.

Phonological Characteristics

In languages that use them phonemically, clicks are fully integrated consonants that can appear in various syllable positions, though they are most common in initial position. They combine with other articulatory features, such as voicing, nasality, and aspiration, to form a series of contrastive phonemes. For example, a single click type like the dental click [ǀ] can have multiple phonological realizations:

• Voiceless velar plosive accompaniment [kǀ]: The click is released simultaneously with a voiceless velar plosive.
• Voiced velar plosive accompaniment [ɡǀ]: The click is released with a voiced velar plosive.
• Nasal velar accompaniment [ŋǀ]: The click is preceded or accompanied by a nasal velar sound.
• Aspirated or delayed aspiration [kǀʰ]: The click release is followed by a puff of air.
• Glottalized or ejective accompaniment [kǀʼ]: The click is released with a glottal constriction.

These accompaniments, sometimes analyzed as the "release" of the posterior closure, are crucial for distinguishing meaning. A single language may have dozens of distinct click phonemes derived from the combination of a few anterior places and several posterior accompaniments.

Geographical and Linguistic Distribution

Clicks are predominantly associated with southern and eastern Africa.

• Khoisan Languages: This is a term of convenience for several language families and isolates that are not Bantu or Afroasiatic and are characterized by extensive click systems. Languages like ǃXóõ (Taa) and Nǁng (South Africa) may have over 80 click consonants, utilizing all five primary places of articulation. The Khoisan families include Kx'a, Tuu, and Khoe-Kwadi.
• Bantu Languages: Clicks were borrowed into several Bantu languages through prolonged contact with Khoisan peoples. Xhosa and Zulu are the most prominent examples, each incorporating three basic click types (dental, alveolar, and lateral). The click inventories in these languages are less extensive than in Khoisan languages but are phonemically vital and used in common vocabulary.
• Other Occurrences: Outside Africa, a very small number of clicks are found. The most notable example is the extinct Australian Aboriginal ceremonial language Damin, which had click sounds as part of its intentionally complex phonological system. Isolated click paralinguistically, such as the bilabial click for a kiss or the dental click for disapproval, are found globally but do not constitute linguistic phonemes in those contexts.

Representation in the International Phonetic Alphabet

The IPA provides a dedicated set of symbols for click consonants, representing the anterior release. The five basic click symbols are: ʘ (bilabial), ǀ (dental), ǃ (alveolar), ǂ (palato-alveolar), and ǁ (alveolar lateral). To denote the posterior accompaniment, these symbols are typically combined with letters for pulmonic consonants. For instance, a dental click with a voiceless velar release is transcribed as [kǀ] or sometimes as a unitary symbol with a tie bar. The IPA chart places clicks in its "Other Symbols" section, highlighting their non-pulmonic airstream mechanism alongside implosives and ejectives.

Historical and Evolutionary Notes

The origin of clicks in human language is a topic of research. Some linguists have suggested that clicks may have been among the earliest speech sounds used by humans, possibly due to their high sonority and carrying power, though this is speculative. Within Africa, it is generally accepted that clicks are an ancient feature of the Khoisan languages and were later adopted by neighboring Bantu-speaking groups through language contact, likely involving intermarriage and cultural exchange. The study of clicks provides significant insight into mechanisms of linguistic borrowing, sound change, and the limits of human phonological systems.