Click letter

The precursors of the current IPA letters, ⟨ǀ⟩ ⟨ǁ⟩ ⟨ǃ⟩ ⟨ǂ⟩, were created by Karl Richard Lepsius[1][2] and used by Wilhelm Bleek[3] and Lucy Lloyd, who added ⟨ʘ⟩.

Also influential were Daniel Jones, who created the letters ⟨ʇ⟩ ⟨ʖ⟩ ⟨ʗ⟩ ⟨ʞ⟩ that were promoted by the IPA from 1921 to 1989, and were used by Clement Doke[4][5] and Douglas Beach.

[7] By the early 19th century, the otherwise unneeded letters ⟨c⟩ ⟨x⟩ ⟨q⟩ were used as the basis for writing clicks in Zulu by British and German missions.

During the First World War, Daniel Jones created the equivalent letters ⟨ʇ⟩ ⟨ʖ⟩ ⟨ʗ⟩ ⟨ʞ⟩ in response to a 1914 request to fill this gap in the IPA, and these were published in 1921 (see history of the International Phonetic Alphabet).

The African reference alphabet proposal has apparently never been used, while the Linguasphere and Lingvarium transcriptions are typewriter substitutions specific to those institutions.

The tenuis–voiced pairs were dental ⟨ʇ ɣ⟩ (the letter ⟨ɣ⟩ had not yet been added to the IPA for the voiced velar fricative), alveolar ⟨ʗ 𝒬⟩, retroflex ⟨ψ ⫛⟩,[28] palatal ⟨ↆ ꙟ⟩ (or ⟨🡣 🡡⟩) and lateral ⟨ʖ ➿︎⟩.

Regardless, separate letters like Doke's and Beach's were never provided by the IPA, and today linguists continue to resort to digraphs or diacritics in a way that is not used for non-click consonants.

Summarized below are the common means of representing voicing, nasalization and dorsal place of articulation, from Bleek's digraphs reflecting an analysis as co-articulated consonants, to those same letters written as superscripts to function as diacritics, reflecting an analysis as unitary consonants, to the combining diacritics for voicing and nasalization.

The following systems are presented in the same order: bilabial, dental ('c'), lateral ('x'), alveolar ('q'), palatal ('v') and retroflex ('‼'), with gaps for missing letters.

If we connect with this our common marks for the cerebral [i.e. retroflex: the sub-dot] or the palatal [i.e. the acute accent], a peculiar notation is wanted only for the lateral, which is the strongest sound.

A Nama man giving a literacy lesson in Khoekhoegowab that includes click letters
The clicks of Xhosa, in the Lepsius alphabet of 1854. The ⟨ṅ⟩ is equivalent to ⟨ ŋ ⟩. The pipe with the acute accent was soon replaced with ⟨ ǂ ⟩.
The click letters created by Carl Jakob Sundevall in 1855 (right column), along with the corresponding Lepsius letters (center).
The 1925 Doke orthography for ʗhũ̬ː ( !Xũ ). Note that "alveolar" (2nd column) corresponds to modern palatal [ǂ] . The letters in the first, third and fifth columns had earlier been used for Zulu. The voiced dental click has the letter ⟨ ɣ ⟩ that would later be used by the IPA for a voiced velar fricative.
Though not clear from this image, the descenders on the nasal clicks that bend to the right bear rings, while those that bend to the left are tails as in IPA ŋ and ɲ . That is, the nasal click letters are, respectively, n with a ring on the right leg, ŋ with a ring on the left leg, n with a ring on the left leg, ɲ with a ring on the right leg, and n with rings on both legs, or, in the order of the main table, .
The clicks of Khoekhoe in the Beach alphabet of 1938. The series are (left to right) dental, alveolar, lateral and palatal. In modern orthography, the last column is ǂg ǂn ǂkh ǂ ǂh .
Zulu click letters of the Norwegian mission