Editing Thai language (section)

== History ==
{{More citations needed section|date=May 2020}}
Thai has undergone various historical sound changes. Some of the most significant changes occurred during the evolution from Old Thai to modern Thai.<ref name="Wilaiwan" /> The Thai writing system has an eight-century history and many of these changes, especially in consonants and tones, are evidenced in the modern [[Thai script|orthography]].

===Early spread===
According to a Chinese source, during the [[Ming dynasty]], [[Yingya Shenglan]] (1405–1433), [[Ma Huan]] reported on the language of the [[Ayutthaya kingdom|Xiānluó]] (暹羅) or Ayutthaya Kingdom,{{efn|Xiānluó was the Chinese name for Ayutthaya, a kingdom created by the merger of [[Lavo Kingdom|Lavo]] and [[Sukhothai Kingdom|Sukhothai]] or Suvarnabhumi.}} saying that it somewhat resembled the local patois as pronounced in [[Guangdong]]<ref>{{Citation|title=Ying-yai Sheng-lan: The Overall Survey of the Ocean's Shores (1433)|date=1970|publisher=Hakluyt Society at the University Press|isbn=0-521-01032-2}}</ref>{{rp|107}} [[Phra Nakhon Si Ayutthaya (city)|Ayutthaya]], the old capital of Thailand from 1351 - 1767 A.D., was from the beginning a bilingual society, speaking Thai and [[Khmer language|Khmer]]. Bilingualism must have been strengthened and maintained for some time by the great number of Khmer-speaking captives the Thais took from Angkor Thom after their victories in 1369, 1388 and 1431.<ref>Kasetsiri 1999: 25</ref> Gradually toward the end of the period, a language shift took place. Khmer fell out of use. Both Thai and Khmer descendants whose great-grand parents or earlier ancestors were bilingual came to use only Thai. In the process of language shift, an abundance of Khmer elements were transferred into Thai and permeated all aspects of the language. Consequently, the Thai of the late Ayutthaya Period which later became Ratanakosin or Bangkok Thai, was a thorough mixture of Thai and Khmer. There were more Khmer words in use than Tai cognates. Khmer grammatical rules were used actively to coin new disyllabic and polysyllabic words and phrases. Khmer expressions, sayings, and proverbs were expressed in Thai through transference.

Thais borrowed both the Royal vocabulary and rules to enlarge the vocabulary from Khmer.<ref>Varasarin 1984: 91</ref> The Thais later developed the royal vocabulary according to their immediate environment. Thai and Pali, the latter from Theravada Buddhism, were added to the vocabulary. An investigation of the Ayutthaya Rajasap reveals that three languages, Thai, Khmer and Khmero-Indic were at work closely both in formulaic expressions and in normal discourse. In fact, Khmero-Indic may be classified in the same category as Khmer because Indic had been adapted to the Khmer system first before the Thai borrowed.

===Old Thai===

Old Thai had a three-way tone distinction on "live syllables" (those not ending in a stop), with no possible distinction on "dead syllables" (those ending in a stop, i.e. either {{IPA|/p/, /t/, /k/}} or the [[glottal stop]] that automatically closes syllables otherwise ending in a short vowel).

There was a two-way voiced vs. voiceless distinction among all [[fricative]] and [[sonorant]] consonants, and up to a four-way distinction among [[stop consonant|stops]] and [[affricate]]s. The maximal four-way occurred in [[labial consonant|labials]] ({{IPA|/p pʰ b ʔb/}}) and [[denti-alveolar consonant|denti-alveolars]] ({{IPA|/t tʰ d ʔd/}}); the three-way distinction among [[velar consonant|velars]] ({{IPA|/k kʰ ɡ/}}) and [[palatal consonant|palatals]] ({{IPA|/tɕ tɕʰ dʑ/}}), with the glottalized member of each set apparently missing.

The major change between old and modern Thai was due to voicing distinction losses and the concomitant [[tone split]]. This may have happened between about 1300 and 1600 CE, possibly occurring at different times in different parts of the Thai-speaking area.<ref name="Wilaiwan" /> All voiced–voiceless pairs of consonants lost the voicing distinction:
*Plain voiced stops ({{IPA|/b d ɡ dʑ/}}) became voiceless aspirated stops ({{IPA|/pʰ tʰ kʰ tɕʰ/}}).<ref group=lower-alpha name="Explanation 4">The glottalized stops {{IPA|/ʔb ʔd/}} were unaffected, as they were treated in every respect like voiceless unaspirated stops due to the initial glottal stop. These stops are often described in the modern language as phonemically plain stops {{IPA|/b d/}}, but the glottalization is still commonly heard.</ref>
*Voiced fricatives became voiceless.
*Voiceless sonorants became voiced.
However, in the process of these mergers, the former distinction of voice was transferred into a new set of tonal distinctions. In essence, every tone in Old Thai split into two new tones, with a lower-pitched tone corresponding to a syllable that formerly began with a voiced consonant, and a higher-pitched tone corresponding to a syllable that formerly began with a voiceless consonant (including glottalized stops). An additional complication is that formerly voiceless unaspirated stops/affricates (original {{IPA|/p t k tɕ ʔb ʔd/}}) also caused original tone 1 to lower, but had no such effect on original tones 2 or 3.

The above consonant mergers and tone splits account for the complex relationship between spelling and sound in modern Thai. Modern "low"-class consonants were voiced in Old Thai, and the terminology "low" reflects the lower tone variants that resulted. Modern "mid"-class consonants were voiceless unaspirated stops or affricates in Old Thai—precisely the class that triggered lowering in original tone 1 but not tones 2 or 3. Modern "high"-class consonants were the remaining voiceless consonants in Old Thai (voiceless fricatives, voiceless sonorants, voiceless aspirated stops). The three most common tone "marks" (the lack of any tone mark, as well as the two marks termed ''mai ek'' and ''mai tho'') represent the three tones of Old Thai, and the complex relationship between tone mark and actual tone is due to the various tonal changes since then. Since the tone split, the tones have changed in actual representation to the point that the former relationship between lower and higher tonal variants has been completely obscured. Furthermore, the six tones that resulted after the three tones of Old Thai were split have since merged into five in standard Thai, with the lower variant of former tone 2 merging with the higher variant of former tone 3, becoming the modern "falling" tone.<ref group=lower-alpha name="Explanation 5">Modern [[Lao language|Lao]], [[Isan language|Isan]] and [[Northern Thai language|northern Thai dialects]] are often described as having six tones, but these are not necessarily due to preservation of the original six tones resulting from the tone split. For example, in standard Lao, both the high and low variants of Old Thai tone 2 merged; however, the mid-class variant of tone 1 became pronounced differently from either the high-class or low-class variants, and all three eventually became phonemic due to further changes, e.g. {{IPA|/kr/}} > {{IPA|/kʰ/}}. For similar reasons, Lao has developed more than two tonal distinctions in "dead" syllables.</ref>

==== Old Thai (Sukhothai) consonant inventory ====
{| class="wikitable"
!
! colspan="4" |[[Labial consonant|Labial]]
! colspan="4" |[[Dental consonant|Dental]]/ <br> [[Alveolar consonant|Alveolar]]
! colspan="3" |([[Alveolo-palatal consonant|Alveolo-]]) <br> [[Palatal consonant|Palatal]]
! colspan="3" |[[Velar consonant|Velar]]
! colspan="1" |[[Glottal consonant|Glottal]]
|-
![[Nasal stop|Nasal]]
| colspan="2" |{{IPAblink|m̊}}
{{Lang|th|หม|italic=no}}
| colspan="2" |{{IPAblink|m}}
{{Lang|th|ม|italic=no}}
| colspan="2" |{{IPAblink|n̊}}
{{Lang|th|หน|italic=no}}
| colspan="2" |{{IPAblink|n}}
{{Lang|th|น, ณ|italic=no}}
| colspan="2" |{{IPAblink|ɲ̊}}
{{Lang|th|หญ|italic=no}}
|{{IPAblink|ɲ}}
{{Lang|th|ญ|italic=no}}
| colspan="2" |{{IPAblink|ŋ̊}}
{{Lang|th|หง|italic=no}}
|{{IPAblink|ŋ}}
{{Lang|th|ง|italic=no}}
|
|-
![[Plosive]]/<br />[[Affricate]]
|{{IPAblink|p}}
{{Lang|th|ป|italic=no}}
|{{IPAblink|pʰ}}
{{Lang|th|ผ|italic=no}}
|{{IPAblink|b}}
{{Lang|th|พ, ภ|italic=no}}
|{{IPA|[ʔb]}}
{{Lang|th|บ|italic=no}}
|{{IPAblink|t}}
{{Lang|th|ฏ, ต|italic=no}}
|{{IPAblink|tʰ}}
{{Lang|th|ฐ, ถ|italic=no}}
|{{IPAblink|d}}
{{Lang|th|ท, ธ|italic=no}}
|{{IPA|[ʔd]}}
{{Lang|th|ฎ, ด|italic=no}}
|{{IPAblink|tɕ}}
{{Lang|th|จ|italic=no}}
|{{IPAblink|tɕʰ}}
{{Lang|th|ฉ|italic=no}}
|{{IPAblink|dʑ}}
{{Lang|th|ช|italic=no}}
|{{IPAblink|k}}
{{Lang|th|ก|italic=no}}
|{{IPAblink|kʰ}}
{{Lang|th|ข|italic=no}}
|{{IPAblink|g}}
{{Lang|th|ค, ฆ|italic=no}}
|{{IPAblink|ʔ}}
{{Lang|th|อ|italic=no}}
|-
![[Fricative consonant|Fricative]]
| colspan="2" |{{IPAblink|f}}
{{Lang|th|ฝ|italic=no}}
| colspan="2" |{{IPAblink|v}}
{{Lang|th|ฟ|italic=no}}
| colspan="2" |{{IPAblink|s}}
{{Lang|th|ศ, ษ, ส|italic=no}}
| colspan="5" |{{IPAblink|z}}~{{IPAblink|ʑ}}
{{Lang|th|ซ|italic=no}}
| colspan="2" |{{IPAblink|x}}
{{Lang|th|ฃ|italic=no}}
|{{IPAblink|ɣ}}
{{Lang|th|ฅ|italic=no}}
|{{IPAblink|h}}
{{Lang|th|ห|italic=no}}
|-
![[Trill consonant|Trill]]
| colspan="4" |
| colspan="2" |{{IPAblink|r̊}}
{{Lang|th|หร|italic=no}}
| colspan="2" |{{IPAblink|r}}
{{Lang|th|ร|italic=no}}
| colspan="7" |
|-
![[Approximant consonant|Approximant]]
| colspan="2" |{{IPAblink|ẘ}}
{{Lang|th|หว|italic=no}}
| colspan="2" |{{IPAblink|w}}
'''ว'''
| colspan="2" |{{IPAblink|l̥}}
'''หล'''
| colspan="2" |{{IPAblink|l}}
'''ล'''
|{{IPAblink|j̊}}
'''หย'''
| colspan="4" |
|{{IPAblink|j}}
'''ย'''
|{{IPA|[ʔj]}}
'''อย'''
|}

==== Historical Sukhothai pronunciation ====
{| class="wikitable"
!Letters
!IPA
!Word in Sukhothai (in Modern Thai script)
!Pronunciation in IPA (excluding tone)
!Meaning and Definitions
|-
| colspan="5" |'''<nowiki>วรรค ก | Varga Kor</nowiki>'''
|-
|'''ก'''
|'''k'''
|เกิด
|kɤːt
|''v.'' to be born
|-
|'''ข'''
|'''kʰ'''
|ของ
|kʰɔːŋ
|''n.'' thing
|-
|'''ฃ'''
|'''x'''
|ฃึ้น (ขึ้น)
|xɯn
|''v.'' to go up
|-
|'''ค'''
|'''g'''
|ครู
|gruː
|''n.'' teacher
|-
|'''ฅ'''
|'''ɣ'''
|ฅวาม (ความ)
|ɣwaːm
|''n.'' affair; matter; content
|-
|'''ฆ'''
|'''g'''
|ฆ่า
|gaː
|''v.'' to kill
|-
|'''ง'''
|'''ŋ'''
|งก
|ŋok
|''adj.'' greedy
|-
|'''หง'''
|'''ŋ̊'''
|หงอก
|ŋ̊ɔːk
|''v.'' to whiten (''[[hair]]'')
|-
| colspan="5" |'''<nowiki>วรรค จ | Varga Jor</nowiki>'''
|-
|'''จ'''
|'''tɕ'''
|ใจ
|tɕaɯ
|''n.'' heart
|-
|'''ฉ'''
|'''tɕʰ'''
|ฉาย
|tɕʰaːj
|''v.'' to shine (on something)
|-
|'''ช'''
|'''dʑ'''
|ชื่อ
|dʑɯː
|''n.'' name
|-
|'''ซ'''
|'''z - ʑ'''
|ซ้ำ
|zam
|''adv.'' repeatedly
|-
|'''ญ'''
|'''ɲ'''
|ญวน
|ɲuan
|''n.'' [[Vietnam]] (''archaic'')
|-
|'''หญ'''
|'''ɲ̊'''
|หญิง
|ɲ̊iŋ
|''n.'' woman
|-
| colspan="5" |'''<nowiki>วรรค รฏ | Varga Ra Tor</nowiki>'''
|-
|'''ฎ'''
|'''ʔd'''
|ฎีกา
|ʔdiː.kaː
|''n.'' petition notice
|-
|'''ฏ'''
|'''t'''
|ฏาร
|taː.raʔ
|''n.'' [[Ganymede (moon)|Ganymede]]
|-
|'''ฐ'''
|'''tʰ'''
|ฐาน
|tʰaːn
|''n.'' base, platform
|-
|'''ณ'''
|'''n'''
|เณร
|neːn
|''n.'' novice monk
|-
| colspan="5" |'''<nowiki>วรรค ต | Varga Tor</nowiki>'''
|-
|'''ด'''
|'''ʔd'''
|ดาว
|ʔdaːw
|n. star
|-
|'''ต'''
|'''t'''
|ตา
|taː
|''n.'' [[eye]]
|-
|'''ถ'''
|'''tʰ'''
|ถอย
|tʰɔj
|''v.'' to move back
|-
|'''ท'''
|'''d'''
|ทอง
|dɔːŋ
|''n.'' [[gold]]
|-
|'''ธ'''
|'''d'''
|ธุระ
|du.raʔ
|''n.'' business; affairs; errands
|-
|'''น'''
|'''n'''
|น้ำ
|naːm
|''n.'' [[water]]
|-
|'''หน'''
|'''n̊'''
|หนู
|n̊uː
|''n.'' [[mouse]]
|-
| colspan="5" |'''<nowiki>วรรค ป | Varga Por</nowiki>'''
|-
|'''บ'''
|'''ʔb'''
|บ้าน
|ʔbaːn
|''n.'' house
|-
|'''ป'''
|'''p'''
|ปลา
|plaː
|''n.'' fish
|-
|'''ผ'''
|'''pʰ'''
|ผึ้ง
|pʰɯŋ
|''n.'' [[bee]]
|-
|'''ฝ'''
|'''f'''
|ฝัน
|fan
|''n.'' dream
|-
|'''พ'''
|'''b'''
|พ่อ
|bɔː
|''n.'' father
|-
|'''ฟ'''
|'''v'''
|ฟัน
|van
|''n.'' tooth
|-
|'''ภ'''
|'''b'''
|ภาษา
|baː.saː
|''n.'' [[language]]
|-
|'''ม'''
|'''m'''
|แม่
|mɛː
|''n.'' mother
|-
|'''หม'''
|'''m̊'''
|หมา
|m̊aː
|''n.'' dog
|-
| colspan="5" |'''<nowiki>อวรรค | Avarga</nowiki>'''
|-
|'''อย'''
|'''ʔj'''
|อย่า
|ʔjaː
|''adv.'' do not
|-
|'''ย'''
|'''j'''
|เย็น
|jen
|''adj.'' cold
|-
|'''หย'''
|'''j̊'''
|เหยียบ
|j̊iap
|''v.'' to step on
|-
|'''ร'''
|'''r'''
|รัก
|rak
|''v.'' to love
|-
|'''หร'''
|'''r̊'''
|หรือ
|r̊ɯː
|''conj.'' or
|-
|'''ล'''
|'''l'''
|ลม
|lom
|''n.'' wind
|-
|'''หล'''
|'''l̥'''
|หล่อ
|l̥ɔː
|''adj.'' handsome
|-
|'''ว'''
|'''w'''
|วัน
|wan
|''n.'' day
|-
|'''หว'''
|'''ẘ'''
|หวี
|ẘiː
|''n.'' comb
|-
|'''ศ'''
|'''s'''
|ศาล
|saːn
|''n.'' court of law
|-
|'''ษ'''
|'''s'''
|ฤๅษรี (ฤๅษี)
|rɯː.siː
|''n.'' hermit
|-
|'''ส'''
|'''s'''
|สวย
|suaj
|''adj.'' beautiful
|-
|'''อ'''
|'''ʔ'''
|อ้าย
|ʔaːj
|''n.'' first born son
|}

==== Early Old Thai ====
{{further|Proto-Tai}}
Early Old Thai also apparently had velar fricatives {{IPA|/x ɣ/}} as distinct phonemes. These were represented by the now-obsolete letters ฃ ''kho khuat'' and ฅ ''kho khon'', respectively. During the Old Thai period, these sounds merged into the corresponding stops {{IPA|/kʰ ɡ/}}, and as a result the use of these letters became unstable.

At some point in the history of Thai, an alveolo-palatal nasal phoneme {{IPA|/ɲ/}} also existed, inherited from [[Proto-Tai]]. A letter ญ ''yo ying'' also exists, which is used to represent an alveolo-palatal nasal in words borrowed from [[Sanskrit]] and [[Pali]], and is currently pronounced {{IPA|/j/}} at the beginning of a syllable but {{IPA|/n/}} at the end of a syllable.  Most native Thai words that are reconstructed as beginning with {{IPA|/ɲ/}} are also pronounced {{IPA|/j/}} in modern Thai, but generally spelled with ย ''yo yak'', which consistently represents {{IPA|/j/}}. This suggests that {{IPA|/ɲ/}} > {{IPA|/j/}} in native words occurred in the pre-literary period. It is unclear whether Sanskrit and Pali words beginning with {{IPA|/ɲ/}} were borrowed directly with a {{IPA|/j/}}, or whether a {{IPA|/ɲ/}} was re-introduced, followed by a second change {{IPA|/ɲ/}} > {{IPA|/j/}}. The [[northeastern Thai]] dialect [[Isan language|Isan]] and the [[Lao language]] still preserve the phoneme /ɲ/, which is represented in the [[Lao script]] by  ຍ, such as in the word  ຍຸງ ({{IPA|/ɲúŋ/}}, ''mosquito''). This letter is distinct from the phoneme {{IPA|/j/}} and its Lao letter ຢ, such as in the word  ຢາ ({{IPA|/jàː/}}, ''medicine''). The distinction in writing has been lost in the informal writing of the Isan language with the Thai script and both sounds are represented by ย {{IPA|/j/}} (See: [[Comparison of Lao and Isan]]).

Proto-Tai also had a glottalized palatal sound, reconstructed as {{IPA|/ʔj/}} in Li Fang-Kuei (1977{{Full citation needed|date=November 2012}}). Corresponding Thai words are generally spelled หย, which implies an Old Thai pronunciation of {{IPA|/hj/}} (or {{IPA|/j̊/}}), but a few such words are spelled อย, which implies a pronunciation of {{IPA|/ʔj/}} and suggests that the glottalization may have persisted through to the early literary period.

=== Vowel developments ===
The vowel system of modern Thai contains nine pure vowels and three centering diphthongs, each of which can occur short or long. According to Li (1977{{Full citation needed|date=November 2012}}), however, many Thai dialects have only one such short–long pair ({{IPA|/a aː/}}), and in general it is difficult or impossible to find minimal short–long pairs in Thai that involve vowels other than {{IPA|/a/}} and where both members have frequent correspondences throughout the Tai languages.  More specifically, he notes the following facts about Thai:
*In [[open syllable]]s, only long vowels occur. (This assumes that all apparent cases of short open syllables are better described as ending in a glottal stop.  This makes sense from the lack of tonal distinctions in such syllables, and the glottal stop is also reconstructible across the Tai languages.)
*In [[closed syllable]]s, the long high vowels {{IPA|/iː ɯː uː/}} are rare, and cases that do exist typically have diphthongs in other Tai languages.
*In closed syllables, both short and long mid {{IPA|/e eː o oː/}} and low {{IPA|/ɛ ɛː ɔ ɔː/}} do occur.  However, generally, only words with short {{IPA|/e o/}} and long {{IPA|/ɛː ɔː/}} are reconstructible back to Proto-Tai.
*Both of the mid back unrounded vowels {{IPA|/ɤ ɤː/}} are rare, and words with such sounds generally cannot be reconstructed back to Proto-Tai.
Furthermore, the vowel that corresponds to short Thai {{IPA|/a/}} has a different and often higher quality in many of the Tai languages compared with the vowel corresponding to Thai {{IPA|/aː/}}.

This leads Li to posit the following:
#Proto-Tai had a system of nine pure vowels with no length distinction, and possessing approximately the same qualities as in modern Thai: high {{IPA|/i ɯ u/}}, mid {{IPA|/e ɤ o/}}, low {{IPA|/ɛ a ɔ/}}.
#All Proto-Tai vowels were lengthened in open syllables, and low vowels were also lengthened in closed syllables.
#Modern Thai largely preserved the original lengths and qualities, but lowered {{IPA|/ɤ/}} to {{IPA|/a/}}, which became short {{IPA|/a/}} in closed syllables and created a phonemic length distinction {{IPA|/a aː/}}.  Eventually, length in all other vowels became phonemic as well and a new {{IPA|/ɤ/}} (both short and long) was introduced, through a combination of borrowing and sound change.  Li believes that the development of long {{IPA|/iː ɯː uː/}} from diphthongs, and the lowering of {{IPA|/ɤ/}} to {{IPA|/a/}} to create a length distinction {{IPA|/a aː/}}, had occurred by the time of Proto-Southwestern-Tai, but the other missing modern Thai vowels had not yet developed.

Not all researchers agree with Li. Pittayaporn (2009{{Full citation needed|date=November 2012}}), for example, reconstructs a similar system for Proto-Southwestern-Tai, but believes that there was also a mid back unrounded vowel {{IPA|/ə/}} (which he describes as {{IPA|/ɤ/}}), occurring only before final velar {{IPA|/k ŋ/}}.  He also seems to believe that the Proto-Southwestern-Tai vowel length distinctions can be reconstructed back to similar distinctions in Proto-Tai.