Comparison of Lao and Thai
Lao and Thai are two closely related languages of the Southwestern branch of Tai languages. Lao falls within the Lao-Phuthai group of Southwestern Tai languages and Thai within the Chiang Saen language group. Lao (including Isan) and Thai, although they occupy separate groups, are mutually intelligible and were pushed closer through contact and Khmer influence, but all Southwestern Tai languages are mutually intelligible to some degree. Isan refers to the local development of the Lao language in Thailand, as it diverged in isolation from Laos, under Thai influence. The Isan language is still referred to as Lao by native speakers. Spoken Lao is mutually intelligible with Thai and Isan to such a degree that their speakers are able to effectively communicate with one another speaking their respective languages. These languages are written with slightly different scripts, the Lao script and Thai script, but are linguistically similar and effectively form a dialect continuum. Although Thai and Lao (including Isan) are mutually intelligible, Thai speakers without previous exposure to the Isan language encounter several difficulties parsing the spoken language. Isan, written according to Thai etymological spelling, is fairly legible to Thai as the two languages share more than eighty percent cognate vocabulary, similar to the relationship between Spanish and Portuguese as changes in the meanings of terms, retention of archaisms, slightly different grammar and some vocabulary differences blur the close relationship. The relationship is asymmetric, with Isan speakers able to understand spoken and written Thai quite well due to its mandatory use in school and the popularity of Thai media and participation in Thai society, but many Isan students suffer the shock of switching from the Isan language of the home to the Central Thai-only primary school. False friends
Many Lao terms are very similar to words that are profane, vulgar or insulting in the Thai language, features that are much deprecated. Lao uses ອີ່ ( and ອ້າຍ/archaic ອ້າຽ (), to refer to young girls and slightly older boys, respectively. In Thai, the similarly sounding อี, i () and ไอ้, ai () are often prefixed before a woman's or man's name, respectively, or alone or in phrases that are considered extremely vulgar and insulting. These taboo expressions such as อีตัว "i tua", "whore" () and ไอ้บ้า, "ai ba", "son of a bitch" (). Phonological differences

Thai and Lao share a similar phonology, being closely related languages, however, several developments occurred in Lao that clearly distinguish them. Tone, including patterns and quality, is the largest contributing factor and varies widely between varieties of Lao, but together they share splits quite distinct to Standard Thai and other Central Thai speech varieties. There are also several key sound changes that occurred in the Lao language that differentiates it from Thai. Consonantal differences
Lao lacks the /r/ of formal Thai, replacing it with /h/ or /l/, as well as /t͡ɕʰ/, which is replaced by /s/. Lao also has the consonant sounds /ɲ/ and /ʋ/, which are absent in Thai. Aside from these differences, the consonantal inventory is mostly shared between the two languages. C1C2 > C1
Unlike Thai, the only consonant clusters that traditionally occur is C/w/, limited in Lao to /kw/ and /kʰw/ but only in certain environments as the /w/ is assimilated into a diphthongization process before the vowels /aː/, /am/, /aːj/ and /a/ thus limiting their occurrence. For example, Isan kwang (,  kouang, ) is pronounced *kuang (*, *) but kwaen as in kwaen ban (,  khoèn ban, ), 'to feel at home', has a vowel that does not trigger the diphthongization. The consonant clusters of Proto-Tai had mostly merged in Proto-Southwestern Tai, but clusters were re-introduced with Khmer, Sanskrit, Pali and European loan words, particularly C/l/ and C/r/. Lao simplified the clusters to the first element, but sporadically maintained its orthographic representation as late as the early twentieth century although their pronunciation was simplified much earlier. This was likely an influence of Thai. In some instances, some loan words are sometimes pronounced with clusters by very erudite speakers in formal contexts or in the speech of Isan youth that is very Thaified, otherwise the simplified pronunciation is more common. Lao speakers, especially erudite speakers may write and pronounce prôkram (, ), via French  (), and maitri (, ) from Sanskrit maitri (, ) are common, more often than not, they exist as pôkam (, ) and maiti (, ), respectively. Similarly, Isan speakers always write and sometimes pronounce, in 'Thai fashion', maitri (, ) and prokraem (, ), via English 'programme' or 'program' (US), but most speakers reduce it to  and , respectively, in normal speech. /r/ > /h/
Proto-Southwestern Tai initial voiced alveolar trill /r/ remained /r/ in Thai, although it is sometimes pronounced /l/ in informal environments, whereas Lao changed the sound to the voiceless glottal fricative /h/ in these environments. The sound change likely occurred in the mid-sixteenth century as the Tai Noi orthography after that period has the letter Lao letter '' /h/, which was a variant of '' /r/ used to record the sound change. The change also included numerous small words of Khmer origin such as hian , ), 'to learn', which is rian (, ) in Thai, from Khmer riĕn (, ). /r/ > /l/
The shift of Proto-Southwestern Tai */r/ to /h/ in Lao was inconsistent, with some factors that prevented the transition. Instead, these situations led to the shift of /r/ to the alveolar lateral approximant /l/, similar as to what occurs in informal, casual Thai. Polysyllabic loan words from Khmer as well as Indic sources such as Khmer and Pali may have seemed too 'foreign' compared to the monosyllabic loan words that may have been regarded as native, somewhat similar to English 'beef', ultimately from French boeuf but fully anglicized in spelling and pronunciation, versus more evidently French loan words such as crème anglaise, which retains a more French-like pronunciation. Thai speakers sometimes use /l/ in place of /r/ in relaxed, basilectal varieties but this is deprecated in formal speech. rasa ( raxa, ) from Sanskrit rājā (, ), 'king', cf. Thai racha (, ), 'king'
 raka (, ), 'price' from Sanskrit rāka (, ), 'wealth', cf. Thai raka (, )
 charoen ( chaluen, ), 'prosperity', from Khmer camraeum (, ), cf. Thai charoen (, )
 rabam (, , 'traditional dance', from Khmer rôbam (, ), cf. Thai rabam (, )

Lao and Thai both have digraphs, or in the case of Lao ligatures, that consist of a silent /h/ that was historically pronounced at some ancient stage of both languages, but now serves as a mark of tone, shifting the sound to a high-class consonant for figuring out tone. The /h/ may have prevented the assimilation of these words to /h/, as these end up as /l/ in Lao. Similarly, this may have also prevented /r/ to /h/ in Khmer loan words where it begins the second syllable. rue ( lu, ) versus rue (, ), 'or' (conjunction)
 lio (,  versus ri (, ), 'to squint' (one's eyes)
 kamlai (, ), 'profit', from Khmer kâmrai (, ), cf. Thai kamrai (, )
 samrap ( samlap, ), 'for' (the purpose of, to be used as, intended as), from Khmer sâmrap (, ), cf. Thai samrap (, )

There are a handful of words where the expected conversion to /h/ did not take place, thus yielding /l/. In some cases, even in the Lao of Laos, this can be seen as historic Siamese influence, but it also may have been conservative retentions of /r/ in some words that resisted this change. For example, Isan has both hap (, , ) and lap (, , ), both of which mean 'to receive' and are cognates to Thai rap (, ), and the lap variety in Isan and parts of Laos, especially the south, may be due to Thai contact. In other cases, it is because the words are recent loans from Thai or other languages. In Isan, younger speakers often use /l/ in place of /h/ due to language shift. ro (, ), 'to wait, to wait for', cf. Thai ro (, )
 rot ( lôt, ), 'car' or 'vehicle', cf. Thai rot (, )
 lam (, ), 'to dance', cf. Thai ram (, )
 rom ( rôm, ), 'Rome', cf. Thai rom (, )
 rangkai (, ) (Isan youth), traditionally hangkai (, , ), 'body' (anatomic), cf. Thai rangkai (, )

/tɕʰ/ > /s/
Proto-Tai */ɟ/ and */ʑ/ had merged into Proto-Southwestern Tai */ɟ/, which developed into /tɕʰ/ in Thai, represented by the Thai letter ''. Only a small handful of Proto-Tai words with */č/ were retained in Proto-Southwestern Tai, represented by the Tai letter '', but this also developed into /tɕʰ/ in Thai and most words with '' are either Khmer, Sanskrit or more recent loan words from Chinese dialects, particularly Teochew (Chaoshan Min). Thai also uses the letter '' which only occurs in a handful of Sanskrit and Pali loan words where it represented /ɟʱ/, but in Thai has the pronunciation /tɕʰ/. Lao has developed /s/ where Thai has /tɕʰ/, with the letter '' /s/, but romanized as 'x', is used to represent cognate words with Thai '' or '' whereas Thai '' is replaced by Lao '' /s/ in analogous environments. Isan speakers will sometimes substitute the Thai letter '' /s/ in place of Thai '' /tɕʰ/ in cognate words, but this is never done to replace '' /tɕʰ/ and sometimes avoided in formal, technical or academic word of Khmer, Sanskrit and Pali origins even if the pronunciation is still /s/, although educated Isan speakers and Isan youth may you use /tɕʰ/ due to code-switching or language shift. Similarly, the letter '' /tɕʰ/ is usually retained even if it is better approximated by tone and phonology by '' /s/ as is done in similar environments in Lao. Proto-Tai etymon. Pre-1975 Lao spelling. /j/ < /ŋ/ and /j/
Lao retains a distinction with some words retaining a voiced palatal nasal /ɲ/ from the merger Proto-Southwestern Tai */ɲ/ and */ʰɲ/ and some words with /j/ derived from the merger of Proto-Southwestern Tai */j/ and */ˀj/. The change may have persisted into Thai after the adoption of writing, as some words provide clues to their etymology. For example, Proto-Southwestern Tai */ɲ/ and */ʰɲ/ correspond to the Central and Southern Thai spellings '' and '' whereas */j/ and */ˀj/ correspond to Central and Southern Thai spellings '' and '', respectively, all of which have merged in pronunciation to /j/ in Thai, although as this pronunciation was likely lost shortly after literacy, not all Thai words have this corresponding spelling. Thai also uses the letter '' in words of Khmer, Sanskrit and Pali where the source language has /ɲ/ but these words now have /j/ pronunciation. Lao maintains the distinction with the letters '' /ɲ/ and '' /j/, but /j/ is a rarer outcome in Lao and most instances of Thai '' and '' or digraphs '' and '' will result in Lao '' /ɲ/ or '' /ɲ/. With a few exceptions, only Proto-Southwestern Tai */ˀj/ yields /j/. Lao, unlike Thai, has also adopted Khmer, Sanskrit and Pali loan words and retains the /ɲ/ pronunciation of the loan source languages, but has also converted the consonantal /j/ into /ɲ/ in borrowings. The Lao letter '' also represents /j/, but only in diphthongs and triphthongs as a final element. As the Lao language of Isan is written in Thai according to Thai spelling rules, the phonemic distinction between /j/ into /ɲ/ cannot be made in the orthography, thus Isan speakers write ya '', which suggests ya (, ), 'medicine' but is also used for [n]ya (, , ), an honorary prefix used to address a person who is same in age as one's grandparents. These are distinguished in Lao orthography, but Isan speakers either use context or a tone mark, as they differ in tone, to differentiate the words. Proto-Southwestern Tai etymon. Pre-1975 alternate Lao spelling. /m/ > /l/
The Proto-Southwestern Tai cluster *ml was simplified, producing an expected result of /l/ in Thai and /m/ in Lao. The Saek language, a Northern Tai language distantly related to Thai and Lao preserves these clusters. For instance, Proto-Southwestern Tai *mlɯn, 'to open the eyes', is mlong in Saek (, , ) but appears as luem (, ) and muen (,  mun, ) in Lao. /w/ > /ʋ/
Lao speakers generally pronounce cognates of Thai with initial /w/ as the voiced labiodental approximant /ʋ/, similar to a faint 'v', enough so that the French chose 'v' to transcribe the Lao letter '' /ʋ/. The letter is related to Thai '' /w/. The sound /ʋ/ is particularly noticeable in the Vientiane and Central Lao dialects, with a strong pronunciation favored by the élite of Vientiane. In Isan, the rapid but forced resettlement of the people of Vientiane and surrounding areas to the right bank greatly boosted the Lao population, but likely led to some dialect leveling, which may explain the prevalence of /ʋ/ throughout the region, regardless of personal Isan dialect. The replacement is not universal, especially in Laos, but a shift towards /w/ is also occurring in Isan due to the persistent pressures of the Thai language since the sound /ʋ/ is considered provincial, being different from Thai, as opposed to Laos where it is the prestigious pronunciation. Due to the difference in pronunciation, the French-based system used in Laos uses 'v' whereas the English-based Thai system of romanization uses 'w', so the Lao city of Savannakhét would be rendered 'Sawannakhet' if using the Thai transcription. /k/ > /t͡ɕ/
Another influence of the massive migration of the people of Vientiane to the right bank is the common tendency to replace the voiceless velar plosive /k/ with the voiceless alveolo-palatal affricate /t͡ɕ/. For instance, the people of the city of Khon Chaen, more generally referred to as Khon Kaen (,  Khon Kèn, ) in formal contexts, refer to their city as Khon Chaen (, *, ) in more relaxed settings. In Laos, this is particularly an informal feature specific to Vientiane Lao but is not used in the official written and spoken standard as it is an informal variant, whereas in Isan, it is commonly used but deprecated as a regional mispronunciation. It is also limited to certain words and environments. Vocalic differences

C/w/ diphthongization
Lao innovated a diphthongization that assimilates the /w/ in instances of /kw/ and /kʰw/ in certain environments. This is triggered by the vowels /a/, /aː/, /aːj/ and /am/, but the cluster is retained in all other instances. The /w/ is converted to /uː/ and the vowel is shortened to /ə/. This is not shown in the orthography, as it must have evolved after the adoption of the Lao script in the fourteenth century. Cognate words in Lao where this diphthongization occurs have no alteration in spelling from Thai counterparts. For example, the Thai word for 'to sweep' is kwat (, ) but is kwat ( kouat, ) and has the suggested pronunciation  but is pronounced *kuat (* kouat). The counterpart of Thai khwaen (, ), 'to hang' (something) is also khwaen ( khwèn, ) since the vowel /ɛː/ does not trigger diphthongization. The vowels /a/, /aː/, /aːj/ and /am/ correspond to Thai '', '', '' and '' and the Lao '', '', '' and ''. The clusters that can undergo this transformation are /kw/, Thai '' and Lao '' or /kw/, Thai '' and ' and Lao '' and ''. The non-diphthongized pronunciations as used in Thai are also used by some Isan speakers as a result of Thai influence. In Laos, non-diphthongization is not incorrect, but may sound like a Thai-influenced hypercorrection or very pedantic. As it is the normal pronunciation in Laos and Isan, it limits the instances of consonant clusters that are permissible. /ua/ > /uːə/
The Thai diphthongs and triphthongs with the component /ua/ undergo a lengthening of the /u/ to /uː/ and shortens the /a/ to /ə/, although the shortened diphthong can sound like /uː/ to Thai speakers. In Thai, this includes the vowels /ua/ represented medially by '' and finally by '', /uaʔ/ by '' and the final triphthong /uaj/ by ''. Lao has /uːə/ represented medially by '' and finally by '', /uːəʔ/ by '' and the final triphthong /uːəj/ by ''. This may have been another innovation, like C/w/ diphthongization, that occurred after the adoption of writing as it is not represented orthographically. /ɯ/ > /ɨ/
The close back unrounded vowel /ɯ/ is centralized to the close central unrounded vowel /ɨ/ in Lao, which is not found in Thai. This also applies to all variants of /ɯ/ that occur in Thai, i.e., all cognates with instances of Thai /ɯ/ are Lao /ɨ/, including diphthongs and triphthongs that feature this vowel element. Some very traditional dialects of Southern Lao and the Phuan dialect front the vowel all the way to /iː/. /ɤ/ > /ɘ/
The close-mid back unrounded vowel /ɤ/ is centralized to the close-mid central unrounded vowel /ɘ/ in Lao. Similar to the conversion of /ɯ/ to /ɨ/, it also affects all instances in diphthongs as well. Epenthetic vowels
Abugida scripts traditionally do not notate all vowels, especially the short vowel /a/, usually realized as /aʔ/ in Thai and Lao phonology. This especially affects the polysyllabic loan words of Sanskrit, Pali or Khmer derivation. Instances of when or when not to pronounce a vowel have to be learned individually as the presence of the vowel is inconsistent. For example, the Sanskrit word dharma (, ), which can mean 'dharma', 'moral' or 'justice', was borrowed into Thai as simply tham ( ). As a root, it appears as simply tham as in thamkaset ( ) 'land of justice' or 'righteous land' with the /aʔ/ or thammanit ( ), 'moral person' with /aʔ/. This is not always justified by etymology, as the terms derive from Sanskrit dharmakṣetra (, )—actually signifies 'pious man' in Sanskrit—and dharmanitya (, ), respectively, both of which feature a pronounced but unwritten /a/. Lao and most Isan speakers in relaxed environments will pronounce the 'extra' vowel yielding *thammakaset (,  thammakasét, ) and thammanit (, , ). There are also instances where Thai has the epenthetic vowel lost in Lao, such as krommathan (, ), 'debt contract', whereas Lao has nativized the pronunciation to kromtham ( kômtham, ). This is an exception, as the extra vowel is a sign of Lao-retained pronunciation such as Thai chit (, ), 'paiting' from Sanskrit citra (, ), which is chit (, , ), chit[ta] (,  chitta, ) or extremely epentheticized chit[tara] (,  chittala,  in Isan. As another feature of Isan that deviates from Thai, it is deprecated. Few Isan people are aware that the stigmatized pronunciations are actually the 'proper' Isan form inherited from Lao. Many of these loan words are limited to academic and formal contexts that usually trigger code-switching to formal Thai, thus Isan speakers may pronounce these words more akin to Thai fashion although to varying degrees of adaptation to Isan pronunciation. Lao speakers also tend to insert epenthetic vowels in normal speech, as opposed to standard Thai where this is less common, thus 'softening' the sentence and making dialogue-less staccato. For instance, the Isan phrase chak noi (,  ), which means 'in just a bit' is often pronounced chak-ka noy (*จักกะน้อย , cf. Lao *ຈັກກະນ້ອຍ) but this may be perceived as 'slurred' speech to Thai speakers. Basilectal Isan pronunciation based on historic Lao usage. 'Lao-ified' pronunciation influenced by formal Thai. Hypercorrection amongst the educated to approximate Sanskrit pronunciation. Grammatical differences

Classifiers

Pronouns
Although all the Tai languages are pro-drop languages, which omit pronouns if their use is unnecessary due to context, especially in informal contexts, they are restored in more careful speech. Lao frequently uses the first- and second-person pronouns and rarely drops them in speech compared to Thai, which can sometimes seem more formal and distant. More common is to substitute pronouns with titles of professions or extension of kinship terms based on age, thus it is very common for lovers or close friends to call each other 'brother' and 'sister' and to address the very elderly as 'grandfather' or 'grandmother'. Isan traditionally uses the Lao-style pronouns, although in formal contexts, the Thai pronouns are sometimes substituted as speakers adjust to the socially mandated use of Standard Thai in very formal events. To turn a pronoun into a plural, it is most commonly prefixed with mu ( ) but the variants tu ( ) and phuak ( ) are also used by some speakers. These can also be used for the word hao, 'we', in the sense of 'all of us' for extra emphasis. The vulgar pronouns are used as a mark of close relationship, such as long-standing childhood friends or siblings and can be used publicly, but they can never be used outside of these relationships as they often change statements into very pejorative, crude or inflammatory remarks. Tones

Even Thai words with clear cognates in Lao can differ remarkably by tone. Determining the tone of a word by spelling is complicated. Every consonant falls into a category of high, middle or low class. Then, one must determine whether the syllable has a long or a short syllable and whether it ends in a sonorant or plosive consonant and, if there are any, whatever tone marks may move the tone. Thai กา ka, crow, has a middle tone in Thai, as it contains a mid-class consonant with a long vowel that does not end in a plosive. In Standard Lao, the same environments produce a low-rising tone  but is typically  or rising-mid-falling in Western Lao. Despite the differences in pattern, the orthography used to write words is nearly the same in Thai and Lao, even using the same tone marks in most places, so it is knowing the spoken language and how it maps out to the rules of the written language that determine the tone. However, as the Tai languages are tonal languages, with tone being an important phonemic feature, spoken Lao words out of context, even if they are cognate, may sound closer to Thai words of different meaning. Thai คา kha , 'to stick' is cognate to Lao ຄາ, which in Vientiane Lao is pronounced , which may sound like Thai ค้า kha , 'to trade' due to similarity in tone. The same word in some parts of Isan near Roi Et Province would confusingly sound to Thai ears like ขา kha  with a rising tone, where the local tone patterns would have many pronounce the word with a rising-high-falling heavier on the rising. Although a native Thai speaker would be able to pick up the meaning of the similar words of Lao through context, and after a period of time, would get used to the different tones (with most Lao speech varieties having an additional one or two tones to the five of Thai), it can cause many initial misunderstandings. Lexical differences
Although the majority of Lao words are cognate with Thai, many basic words used in everyday conversation lack cognates in Thai. Some usages vary only by frequency or register. For instance, the Thai question word 'เท่าไหร่' is cognate with Lao 'ເທົ່າໃດ' , but Lao tends to use a related variant form 'ท่อใด'  and 'ທໍ່ໃດ' , respectively, more frequently, although the usage is interchangeable and preference probably more related to region and person. In other areas, Lao preserves the older Tai vocabulary. For example, the old Thai word for a 'glass', such as a 'glass of beer' or 'glass of water' was 'จอก' chok , but this usage is now obsolete as the word has been replaced by Thai 'แก้ว' kaew . Conversely, Lao continues to use 'ຈອກ' chok to mean 'glass' (of water) as , but Lao 'ແກ້ວ' kéo  retains the earlier meaning of Thai 'แก้ว' as 'gem', 'crystal' or 'glass' (material) still seen in the names of old temples, such as 'Wat Phra Kaew' or 'Temple of the Holy Gem'. Nonetheless, a lot of cognate vocabulary is pronounced differently in vowel quality and tone and sometimes consonant sounds to be unrecognizable or do not share a cognate at all. For example, Lao ບໍ່  bo is not related to Thai ไม่ , mai

 1 Thai เท่าไหร่ is cognate to Lao ເທົ່າໃດ, thaodai, . 2 Thai แก้ว also exists as Lao ແກ້ວ,kèo , but has the meaning of "gem". 3 Thai ทำ also exists as Lao ທຳ, tham, . 4 Lao ເຮືອນ also exists as formal Thai เรือน, reuan . 5 Thai บ้าน also exists as Lao ບ້ານ, bane, . 6 Thai จริง also exists as Lao ຈິງ, ching, . See also
Comparison of Lao and Isan

References

Thai language
Lao language
Language comparison