|Sound change and alternation|
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Debuccalization is a sound change in which an oral consonant loses its original place of articulation, moving it to the glottis (usually [h], [ɦ], or [ʔ]). The pronunciation of a consonant as [h] is sometimes called aspiration but, in phonetics, aspiration is the burst of air accompanying a stop. The word comes from Latin bucca, meaning "cheek".
Debuccalization is usually seen as a sub-type of lenition, often defined as a consonant mutation involving the weakening of a consonant by progressive shifts in pronunciation
Debuccalization processes occur in many different types of environments, for example:
- word-initially, as in Kannada
- word-finally, as in Burmese
- intervocalically, as in a number of English varieties (e.g. litter [ˈlɪʔə])
Glottal stop 
British and American English 
Most English-speakers in England and many speakers of American English debuccalize /t/ to a glottal stop [ʔ] in two environments: in word-final position before another consonant—
- get ready [ˈɡɛʔˈɹɛɾi]
- not much [ˈnɑʔˈmʌtʃ]
- not good [ˈnɑʔˈɡʊd]
- it says [ɪʔˈsɛz]
- Milton [ˈmɪlʔn̩]
- Martin [ˈmɑɹʔn̩]
- mountain [ˈmaʊnʔn̩]
- cotton [ˈkɑʔn̩]
Cockney English 
The Bavarian dialect debuccalizes any p, t, k, b, d, g that occurs between two consonants (a situation often produced by vowel elision in the same dialect) and replaces them by [ʔ]. Thus Antn (ducks) and Andn (Andes) are both pronounced [anʔn], although speakers think it is the t or d they are pronouncing. With frequency depending on the location, hàn(d) ("are") occurs instead of the other (and altogether more general) Bavarian form sàn(d) (from the German seind, in contemporary German: sind).
Glottal fricative 
- /ts’ad/ → [ts’ah] ('hat')
- /xaz/ → [xah] ('scar')
- /tl’ulʒ/ → [tl’uh] ('rope')
Scottish English 
Before a liquid or nasal, an /h/ was assimilated to the preceding vowel in Attic-Ionic and Doric and to the following nasal in Aeolic. The process is also described as loss of /h/ and subsequent lengthening of a vowel or consonant to keep the syllable the same length (compensatory lengthening).
West Iberian 
In many varieties of Galician as well as in Galician-influenced Spanish, the phoneme /g/ may debuccalize (gheada) to [h] in most or all instances, though [x] and [ħ] are also possible realizations. There is also an inverse hypercorrection process of older or less educated Galician speakers replacing the phoneme /x/ of the Spanish language by [g], what is called gueada.
All over the country, the phoneme /ʁ/ (historically an alveolar trill /r/ that moved to an uvular position by French influence) has a rather long inventory of allophones, or up to [r ç x ɣ ʀ̟ χ ʁ ʀ ħ h ɦ], the first four and latter six being particularly common. Few dialects, such as sulista and fluminense, give preference to voiced allophones; elsewhere, they are common only as coda, before voiced consonants.
In these dialects, especially among people speaking an educated variety of Portuguese, it is usual to the rhotic coda in the syllable rhyme be an alveolar tap, as in European Portuguese and many registers of Spanish, or to be realized as [χ] or [x]. In the rest of the country, it is generally realized as [h], even among speakers that do not have this allophone as the dominant, or deleted entirely, as commonplace in the Vernacular.
But in some mineiro and mineiro-influenced fluminense rural registers, what changes is that [h] is used in the rhyme, but as an allophone of /l/ (while rhotic consonants are most often deleted in the rhyme), a mar-mal merger, instead of the much more common and less stigmatized mau-mal merger characteristic of all Brazilian urban centers with the exception of those bordering Mercosur countries – where coda [ɫ] was preserved –, and the entire North and Northeast regions. It comes from the process of replacing Amerindian languages and línguas gerais by Portuguese, what created [ɹ], [ɻ] and r-colored vowel as allophones of both /ɾ/ (now mostly /ʁ/) and /l/ (now mostly [u̯ ~ ʊ̯]) phonemes in the coda since their native speakers had difficulty with reproducing them (caipira dialect). Latter Portuguese influence from other regions made those allophones get rarer in some areas, but the mar-mal merger did not disappear in these few isolated villages and towns.
Finally, some carioca registers, specially those of the poor and of the youth, debuccalize /s/ (that is, [ɕ ~ ʑ]), but not in the strength of what is done with Spanish. Still, there is the mar-mas merger or even the mar-mais merger: mas mesmo assim "but even so" or mas mesma, sim "though, right, the same (f) one" [ˈmaɦ ˈmeɦmɐ ˈsĩ]; mais light "lighter, more slim", or also "less caloric/fatty" [ˈmaɦ ˈlajtɕ]; mas de mim, não "but from me, no " or mais de mim, não "more from me, not" [ˈmaɦ dʑi ˈmĩ ˈnɜ̃w]. Take note that a coda rhotic in fluminense registers is generally not glottal, with few exceptions, so that a debuccalized /s/ is in most instances not likely to be confused with it.
In Romanian, Moldavian dialect, /f/ becomes [h]; să fie becomes să hie etc. as happened in Old Spanish, Old Gascon and Old Japanese.
Debuccalization can be a feature of loanword phonology. For example, while Korean allows certain coda obstruents, Japanese does not. Those consonants realized in Korean as unreleased voiceless stops ([p˺ t˺ k˺]) in Korean are realized in Japanese as glottal stops:
- [tɕuk˺] → [tɕuʔ] ('porridge')
- [mok˺] → [moʔ] ('neck')
- [mat˺] → [maʔ] ('flavor')
- [tap˺]→ [taʔ] ('tower')
Similarly, debuccalization can be seen in Bahasa Indonesia loans into Selayarese 
- O'Brien, Jeremy Paul (2012), An experimental approach to debuccalization and supplementary gestures
- Smith, Jennifer L. (2008), "X Markedness, faithfulness, positions, and contexts: Lenition and fortition in Optimality Theory", in de Carvalho, Joaquim Brandão; Scheer, Tobias; Ségéral, Philippe, Lenition and Fortition
- Whang, James Dy (2012), "Perception of Illegal Contrasts: Japanese Adaptations of Korean Coda Obstruents", Proceedings of the 36th Annual Meeting of the Berkeley Linguistics Society