Proto-Austroasiatic is the reconstructed ancestor of the Austroasiatic languages. Proto-Mon–Khmer (i.e., all Austroasiatic branches except for Munda) has been reconstructed in Harry L. Shorto's Mon–Khmer Comparative Dictionary, while a new Proto-Austroasiatic reconstruction is currently being undertaken by Paul Sidwell.

Scholars generally date the ancestral language to with a homeland in southern China or the Mekong River valley. Sidwell (2022) proposes that the locus of Proto-Austroasiatic was in the Red River Delta area around .

500 Proto-Austroasiatic etyma were published by Paul Sidwell in 2024.

Phonology Earlier work sought to reconstruct the ancestor of the Mon–Khmer languages, viewed as a primary branch of the Austroasiatic language family alongside the Munda languages. This bifurcate model has been abandoned in favour of a flatter classification since around 2000.Sidwell, Paul (2009). The Austroasiatic Central Riverine Hypothesis. Keynote address, SEALS, XIX. Nevertheless, the Munda, Khasi and Nicobarese languages, whose phonologies are more innovative, are less useful for the reconstruction of PAA phonology, though were relied upon to recognize archaic etyma.

Consonants

A total of 21 or 23 consonants are reconstructed for Proto-Austroasiatic.

+ Proto-Austroasiatic consonants Labial Alveolar Palatal Velar Glottal Nasal Stop unvoiced voiced implosive () Fricative Approximant l j Trill

To account for contrasts found in Katuic languages, Paul Sidwell tentatively added *ʄ to the inventory reconstructed by Harry L. Shorto in 2006. Sidwell (2024) adds *ɕ to explain the modern reflexes s ~ ɕ ~ h ~ j.

Vowels

Sidwell & Rau (2015) reconstruct 8 Proto-Austroasiatic vowels, each of which can occur short or long.

+ Proto-Austroasiatic vowels Height Front Central Back Close Mid Open This differs from Shorto's inventory, which was based on correspondences between Mon and Khmer only, in adding . Sidwell (2023) adds a close central vowel .

Proto-Austroasiatic diphthongs are more difficult, though and are generally recognized. Shorto also reconstructed some forms using and , but Sidwell accounts for these using long vowels , and . Sidwell tentatively suggests and .

Word structure Common word structures in Proto-Austroasiatic include *CV(C) and *CCV(C) roots. *CVC roots can also be affixed either via prefixes or infixes, as in *C-CVC or *CVC. Sidwell and Rau (2015) propose the following syllable structure for Proto-Austroasiatic.Sidwell, Paul. 2018. Austroasiatic Studies: state of the art in 2018 . Presentation at the Graduate Institute of Linguistics, National Tsing Hua University, Taiwan, May 22, 2018.

*Ci(Cm)VCf

Medial consonants (Cm) are *-w -, *-r -, *-l -, *-j -, and *-h-. All of the Proto-Austroasiatic consonants except for implosives and voiced stops can occur as syllable finals (Cf).

Also possible are sesquisyllables:

*(Cp(n/r/l))CiVCf

All of the Proto-Austroasiatic unvoiced stops and voiced stops, as well as *m-, *N-, *r-, *l-, and *s-, can occur as presyllables (Cp). These may arise from prefixes and infixes. Several daughter languages feature presyllable "coda-copying" from main syllables, which may have been a feature of Proto-Austroasiatic.

The Proto-Austroasiatic word template was later revised as follows by Sidwell (2023).Sidwell, Paul. 2023. How to reconstruct the Proto-Austroasiatic Vowels. ICAAL 11 (11th International Conference on Austroasiatic Linguistics, Chiang Mai 26–27 October 2023). *(Cv(C)).ˈCVC(ˀ)

Hiroz (2024) proposes disyllabic forms for some Proto-Austroasiatic etyma. A few tentative reconstructions are:

#suláː 'leaf' #kuláːʔ 'tiger' #kujáːl 'wind, air' #kil- 'bird, flying animal' (nominal class for birds and flying animals; cf. Old Mon <kil'āk>, <kil'ek>) #kil-ʔáːk 'crow' #kil-láːŋ 'bird of prey'

Morphology Sidwell (2008) considers the two most morphologically conservative Mon–Khmer branches to be Khmuic and Aslian. On the other hand, Vietnamese morphology is far more similar to that of Chinese and the Tai languages and has lost many morphological features found in Proto-Mon–Khmer.

The following Proto-Mon–Khmer affixes, which are still tentative, have been reconstructed by Paul Sidwell.

Nominalizing *-n- (instrumental in Kammu, resultative in Khmu) Nominalizing agentive *-m- Nominalizing iterative (expressive of repetitiveness/numerousness) *-l-/*-r- Nominalizing instrumental *-p- Causative *p(V)- (allomorphs: p-, pn-, -m-) Reciprocal *tr-/*t(N)- Stative *h-/*hN- (?)

Roger Blench (2012) notes that Austroasiatic and Sino-Tibetan share many similarities regarding word structure, particularly nominal affixes (otherwise known as sesquisyllables or minor syllable prefixes). Blench does not make any definitive conclusions about how these similarities could have arisen, but suggests that this typological diffusion might have come about as a result of intensive contact in an area between northern Vietnam, Laos, and northeast Myanmar.Blench, Roger. 2012. The origins of nominal affixes in Austroasiatic and Sino-Tibetan: convergence, contact and some African parallels . Paper presented at the Mainland Southeast Asian Languages: The State of the Art in 2012 workshop, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany, 29 November - 1 December 2012. (slides)

Sidwell & Rau (2014) notice that the Sora-style noun incorporation is also found outside of the Munda branch. Sidwell & Jenny & Alves (2020) further added, that the Munda noun incorporation system and referent indexation in predicates show internal head-first, verb-initial order, which can be taken as more archaic than the verb-final structures at clause/sentence level.

Sora (Sora-Gorum, South Munda):

Bolyu (Pakanic):

Syntax Like the Tai languages, Proto-Mon–Khmer has an SVO, or verb-medial, order. Proto-Mon–Khmer also makes use of noun classifiers and serial verb constructions (Shorto 2006).

However, Paul Sidwell (2018) suggests that Proto-Austroasiatic may have in fact been verb-initial, with SVO order occurring in Indochina due to convergence in the Mainland Southeast Asia linguistic area. Various modern-day Austroasiatic languages display verb-initial word order, including Pnar and Wa (Jenny 2015).Jenny, Mathias. 2015. Syntactic diversity and change in Austroasiatic languages. In Viti, Carlotta (ed.). Perspectives on historical syntax. Amsterdam: John Benjamins, 317–340. Nicobarese also displays verb-initial word order.

Lexicon Below are some Proto-Austroasiatic words relating to animals, plants, agriculture, and material culture from Sidwell (2024).

Invertebrates

Vertebrates

Agriculture

Material culture *ɲaːˀ 'house' *ɗuːŋ 'home, clan territory' *ɟraŋ, *ɟrɔŋ 'post, pillar' *puːŋ, *poaŋ 'window' *Cdaŋ 'walling/fencing material' *taːɲ 'weave (v.)' *ksɛːʔ 'string, cord' *kam 'arrow' *ʔaːkˀ 'bow (n.)'

Numerals are as follows: *muəjˀ, *moːjˀ *ɓaːr *peːˀ *puənˀ *truʔ, *pruʔ *pɔh, *pəɕ *tNɕaːm

Function words Proto-Austroasiatic personal pronouns determiners, and particles are as follows, with reconstructions from Sidwell & Rau (2015) and Shorto (2006).

+PronounsPronounEnglish glossProto-Austroasiatic1s.'I'*ʔaɲ1p. (incl.)'we (incl.)'*ʔiːʔ1p. (excl.)'we (excl.)'*ʔjeːʔ2s.'you (sg.)'*miːʔ/*mi(ː)ʔ 2p.'you (pl.)'*piʔ3s./3p.'third person'*gi(ː)ʔInterrogative (animate)'who'*mVhInterrogative (inanimate)'what'*məh/*m(o)ʔ; *m(o)h

+DeterminersEnglish glossProto-Austroasiatic'that (distal)'*tiːʔ'that (medial)'*tɔʔ 'this (proximal)'*niʔ/*neʔ'here'*nɔ(ː)ʔ

+ParticlesEnglish glossProto-Austroasiatic'used up, finished, lacking'*ʔət; *ʔəːt; *[ʔ]it 'not'*ʔam

Sidwell (2024) revises the personal pronouns as follows.

singular plural 1st person – *hiːˀ ~ *hɛːˀ 2nd person *miːʔ ~ *meːʔ *pɛːʔ 3rd person *ʔan *giːʔ

Branch reconstructions Austroasiatic branch-level reconstructions include: Proto-Munda: Sidwell & Rau (2015) (list) Proto-Khasic: Sidwell (2012)Sidwell, Paul. 2012. Proto Khasic. Mon-Khmer Etymological Database. (list) Proto-Palaungic: Sidwell (2010, 2015)Sidwell, Paul. 2010. Preliminary Notes on Proto Palaungic. Mon-Khmer Etymological Database. (list 1, list 2) Proto-Khmuic: Sidwell (2013)Sidwell, Paul. 2013. Proto Khmuic. Mon-Khmer Etymological Database. (list) Proto-Pakanic: Hsiu (2016)Hsiu, Andrew. 2016. A preliminary reconstruction of Proto-Pakanic. (list) Proto-Vietic: Ferlus (2007)Ferlus, Michel. 2007. Lexique de racines Proto Viet-Muong. Unpublished manuscript. Proto-Katuic: Sidwell (2005)Sidwell, Paul. 2005. The Katuic Languages: classification, reconstruction and comparative lexicon . Munich: Lincom Europa. (list) Proto-Bahnaric: Sidwell (2011)Sidwell, Paul. 2011. Proto Bahnaric. Mon-Khmer Etymological Database. (list) Proto-Khmeric: Sidwell & Rau (2015), based on Ferlus (1992)Ferlus, Michel. 1992. Essai de phonétique historique du khmer (Du milieu du premier millénaire de notre ère à l'époque actuelle). Mon-Khmer Studies 21: 57–89. (list) Proto-Pearic: Sidwell & Rau (2015); Headley (1985)Headley, Robert K. 1985. "Proto-Pearic and the classification of Pearic." In Suriya Ratanakult et al (eds.), Southeast Asian Linguistic Studies Presented to Andre-G. Haudricourt. Institute of Language and Culture for Rural Development, Mahidol University. pp. 428-478. (list) Proto-Monic: Diffloth (1984)Diffloth, Gérard. 1984. The Dvaravati-Old Mon Language and Nyah Kur (Monic Language Studies 1). Bangkok: Chulalongkorn University Printing House. (list) Proto-Aslian: Phillips (2012)Phillips, Timothy C. 2012. Proto-Aslian: towards an understanding of its historical linguistic systems, principles and processes. Ph.D. thesis, Institut Alam Dan Tamadun Melayu Universiti Kebangsaan Malaysia, Bangi. (list) Proto-Nicobarese: Sidwell (2018)Sidwell, Paul. 2018. Proto-Nicobarese phonology. In Papers from the Seventh International Conference on Austroasiatic Linguistics, 101-131. Journal of the Southeast Asian Linguistics Society Special Publication No. 3. University of Hawaii Press. (list)

Origin and dispersal Paul Sidwell (2009) suggested that the likely homeland of Austroasiatic is in the Mekong River region, and that the family is not as old as frequently assumed, dating to perhaps 2,000 BCE.Family Diversity and the Austroasiatic Homeland, Paul Sidwell (abstract)

However, Ilia Peiros (2011) criticized Sidwell's 2009 riverine dispersal hypothesis heavily and claimed many contradictions. He showed with his analysis that the homeland of Austroasiatic is somewhere near the Yangtze. He suggests the Sichuan Basin as likely homeland of proto-Austroasiatic before they migrated to other parts of central and southern China and then into Southeast Asia. He further suggests that the family must be as old as proto-Austronesian and proto-Sino-Tibetan or even older.

George van Driem (2011) proposed that the homeland of Austroasiatic was in the Brahmaputra basin. He further suggested, based on genetic studies, that the migration of Kra–Dai people from Taiwan replaced the original Austroasiatic language but the effect on the people was only minor. Local Austroasiatic speakers adopted Kra-Dai languages and partially their culture.van Driem, George. (2011). Rice and the Austroasiatic and Hmong-Mien homelands. In N. J. Enfield (Ed.), Dynamics of Human Diversity: The Case of Mainland Southeast Asia (pp. 361-390). Canberra: Pacific Linguistics.

Laurent Sagart (2011) and Peter Bellwood (2013) supported the theory of an origin of Austroasiatic along the Yangtze river in southern China.

Genetic and linguistic research in 2015 about ancient people in East Asia suggest an origin and homeland of Austroasiatic in today southern China or even further north.