Editing Vietnamese language (section)

===Origin of tones===
Proto-Vietic did not have tones. Tones developed later in some of the daughter languages from distinctions in the initial and final consonants. Vietnamese tones developed as follows:<ref name="Haudricourt 2017 122–128">{{Cite journal|last=Haudricourt|first=André-Georges|date=2017|title=La place du Vietnamien dans les langues Austroasiatiques|trans-title=The place of Vietnamese in Austroasiatic (1953)|url=https://halshs.archives-ouvertes.fr/halshs-01631477/document|journal=Bulletin de la Société de Linguistique de Paris|volume=49|issue=1|pages=122–128}}</ref>

:{| class="wikitable" style="text-align:center;"
|-
! [[Register (phonology)|Register]]
! Initial consonant
! Smooth ending
! Glottal ending
! Fricative ending
|-
! High (first) register
| Voiceless
| A1 ''ngang'' "level"
| B1 ''sắc'' "sharp"
| C1 ''hỏi'' "asking"
|-
! Low (second) register
| Voiced
| A2 ''huyền'' "deep"
| B2 ''nặng'' "heavy"
| C2 ''ngã'' "tumbling"
|}

Glottal-ending syllables ended with a glottal stop {{IPA|/ʔ/}}, while fricative-ending syllables ended with {{IPA|/s/}} or {{IPA|/h/}}. Both types of syllables could co-occur with a resonant (e.g. {{IPA|/m/}} or {{IPA|/n/}}).

At some point, a [[tone split]] occurred, as in many other [[Mainland Southeast Asia linguistic area|mainland Southeast Asian languages]]. Essentially, an [[allophonic]] distinction developed in the tones, whereby the tones in syllables with voiced initials were pronounced differently from those with voiceless initials. (Approximately speaking, the voiced [[allotone]]s were pronounced with additional [[breathy voice]] or [[creaky voice]] and with lowered pitch. The quality difference predominates in today's northern varieties, e.g. in [[Hanoi]], while in the southern varieties the pitch difference predominates, as in [[Ho Chi Minh City]].) Subsequent to this, the plain-voiced stops became voiceless and the allotones became new phonemic tones.

The implosive stops ({{IPA|ɓ}}, {{IPA|ɗ}} and {{IPA|ʄ}}) were unaffected, and in fact developed tonally as if they were unvoiced.{{citation needed|date=December 2024}} (This behavior is common to all East Asian languages with implosive stops.)
These stops merged with the corresponding nasals ({{IPA|m}}, {{IPA|n}} and {{IPA|ɲ}}) before the Old Vietnamese period.{{sfn|Ferlus|1992|p=117}}{{sfn|Shimizu|2015|p=152}}

As noted above, consonants following minor syllables became voiced fricatives. The minor syllables were eventually lost, but not until the tone split had occurred. As a result, words in modern Vietnamese with voiced fricatives occur in all six tones, and the tonal register reflects the voicing of the minor-syllable prefix and not the voicing of the main-syllable stop in Proto-Vietic that produced the fricative. For similar reasons, words beginning with {{IPA|/l/}} and {{IPA|/ŋ/}} occur in both registers. (Thompson 1976 reconstructed voiceless resonants to account for outcomes where resonants occur with a first-register tone,<ref>{{cite journal
|last=Thompson
|first=Laurence C.
|title=Proto-Viet–Muong Phonology
|journal=Oceanic Linguistics Special Publications
|volume=13
|series=Austroasiatic Studies Part II
|year=1976
|pages=1113–1203
|publisher=University of Hawai'i Press
|jstor=20019198
}}</ref> but this is no longer considered necessary, at least by Ferlus.)

A large number of words were borrowed from [[Middle Chinese]], forming part of the [[Sino-Vietnamese vocabulary]]. These caused the original introduction of the retroflex sounds {{IPA|/ʂ/}} and {{IPA|/ʈ/}} (modern ''s'', ''tr'') into the language.