Hungarian Turkology has traditionally focused on the languages of the Middle Volga region. Chuvash is the only surviving representative of the western branch of the Turkic languages and dialects, and the Old Turkic loanwords in Hungarian prior to the conquest of the Carpathian Basin in 895 are an important source for reconstructing the language history of this group of Turkic languages in the period between the fifth and ninth centuries.¹ The reconstruction of the history of Chuvash rests on Turkic loanwords in neighbouring Finno-Ugric and Slavic languages, as well as on Finno-Ugric and Slavic loanwords in Chuvash, combined with the historical reconstruction of Chuvash. Klára Agyagási studied Turkology under András Róna-Tas and specialized in Chuvash studies, although she did work on Tatar as well. Further, Agyagási was trained in Slavic studies and wrote an important monograph on the Old Russian loanwords in the Turkic languages of the Volga–Kama region (Adjagaši 2005). She worked with Gábor Bereczki to write an etymological dictionary of Cheremis (Bereczki 2013) and is an expert in Finno-Ugric studies. Agyagási's expertise allowed her to determine the chronology of the history of the Chuvash language using novel linguistic methods and to establish the historical consequences of her linguistic conclusions.

Agyagási accepts the term West Old Turkic (WOT), following the work of Róna-Tas and Berta, who indicate that the only survivor of this branch of the Turkic languages is Chuvash. WOT relates to the period of the fifth to thirteenth centuries for these languages. Several other terms relate to this group, such as Bulgar–Turkic, as introduced by Ašmarin, who identified Chuvash with the language spoken by the Volga Bulgars (tenth to thirteenth centuries), extending this further back to the Bulgars of the Eastern European steppe (the fifth to the seventh centuries) (p. 25). The term Chuvash-type Turkic was preferred by Ligeti to emphasize the commonalities the extinct languages have with Chuvash (Ligeti 1986, 9–13). The r-Turkic languages is simply an alternative term for this branch of Turkic languages in linguistical works in opposition to the z-Turkic or Common Turkic languages. Historians have used the phrase Ogur–Turkic as well, to contrast with Oguz, e.g. Peter Golden (1992, 20). Agyagási proposes the following new periodization:

1. 1.The fifth to ninth centuries, WOT/Oguric, i.e. Chuvash-type Turkic languages of Eastern Europe, such as those of the Bulgar, Ogur, Onogur, Saragur and Khazar confederations; the most detailed source for this period is the Old Turkic loanwords in Hungarian (384 words).
2. 2.The tenth to thirteenth centuries, WOT/Volga Bulgar (p. 35), of which three dialects were reconstructed. A dialect of Volga Bulgar developed into Middle Chuvash, while the other two were assimilated and disappeared.
3. 3.Early Middle Chuvash, the thirteenth to fifteenth centuries.
4. 4.Late Middle Chuvash, the sixteenth to seventeenth centuries.
5. 5.Modern Chuvash, the eighteenth to twentieth centuries.

Her book consists of five chapters. The first, ‘The predecessors of the Chuvash in the Volga region’ (pp. 1–33) provides an overview of the history of those peoples who spoke r-Turkic from the fifth century: the Ogurs, Bulgars and Volga Bulgars.

Agyagási devotes a special study to the ethnonym Chuvash (pp. 8–10). The Old Turkic yuγač ‘from the opposite bank’ has three variants in Volga Bulgar dialects: in the form of śuwaś, it was copied by the Cheremis and preserved as suas meaning ‘Tatar’, as ǰuwač/č´́uwač, it is the form of the central VB dialect that was the antecedent of Chuvash (čuvaš), and the third dialectal form is not recorded. It was an appellative in geographic sense, meaning those who lived on the other side of the river identified as either the Volga or the Kama in the tenth to thirteenth centuries. During the Mongol period, the central Volga Bulgar dialect was assimilated by the Kipchaks, while the north-western dialect moved further west and was preserved, eventually becoming Chuvash. At the same time the appellative changed to an ethnonym: the word śuwaś borrowed by the Cheremis was used to describe the central Volga Bulgar dialect that was assimilated by the Kipchaks who migrated to the Volga region en masse after the Mongol invasion. Thus, the term took on the meaning Tatar in Cheremis. The central variant ǰuwač/č́uwač was adopted by the Kipchaks and the ethnonym appeared first in 1502 to describe the people living on the right bank of the Volga. However, it remains unknown how this term came to be used as a self-designation for the Chuvash.

Chuvash linguistic history can be reconstructed from glosses and loanwords left behind from contacts with other languages. In the first chapter, Agyagási discusses the linguistic history of Chuvash, updating and where necessary, revising the findings of Róna-Tas (1982, 113–170). The Proto-Turkic period includes loans to Mongolian and Proto-Samoyedic and loans from Old and Middle Iranian to Proto-Turkic. Old Turkic began with the separation of r-Turkic from Common Turkic in the fifth century, and it ended with the formation of the Mongol Empire. WOT language contacts included loans from Chinese and the WOT loans to Hungarian and Ossetic. The glosses and names of the Danube Bulgars, Khazars and Avars are taken into consideration as a source of WOT. Two Old Russian loans (*gǫba, *kǫdel'a) were borrowed in WOT before the nasalization (tenth century) and nine Old Russian loans were attested in Volga Bulgar dialects (banja ‘bathing house’, cĕpъ ‘a manual tool used for threshing’, degъtъ ‘tar’, kъniga ‘book’, kyjewъ ‘Kiev’, mĕxъ ‘animal hide’, mur'ja ‘chimney’, rusь ‘Russian’, rъžь ‘rye’). There are also Old Turkic loans in Old Russian including Volga Bulgar loans such as trunove < turun < tudun and vataga < otak. The official embrace of Islam of the Volga Bulgars in 922 made possible to use Arabic and Persian loans in Volga Bulgar language. The Volga Bulgars came into contact with the local Finno-Ugric speaking communities speaking Proto-Permic and Mordvin languages. The beginning of Middle Turkic period is marked by the formation of the Mongol empire in the first half of the thirteenth century. The sources of this period include the epitaphs, the so-called Volga Bulgar tomb inscriptions from the thirteenth-fourteenth centuries, the Middle Mongolian loans in Middle Chuvash, Middle Bulgarian loans in Mari, Proto-Mari, Middle Kipchak and Middle Russian loans in Middle Chuvash. The Modern Chuvash period starts with the appearance of records in Chuvash in the eighteenth century representing the Chuvash dialects: Viryal and Anatri.

The second chapter discusses the oppositions in the Oguric consonant system (Proto-Turkic and Old Turkic period). The changes of consonants regarded as Chuvash-type Turkic/WOT characteristics have been put in chronological order in this chapter. The rhotacism (z>r), lambdacism (š>l) are basic characteristics of this language group, sometimes called r-Turkic. The z>r change can be dated before the second century A.D., i.e. in the Proto-Turkic period. Both changes were spread in the Chuvash-type Turkic languages. The y->ǰ- change in Proto-Turkic included not only the Chuvash-type Turkic but other Turkic language subgroups (Kipchak and Siberian).

During the WOT Oguric period the consonant ǰ- lost its voice and was palatalized: č́-. The loans in Hungarian with initial d´- (gy-) reflect the earlier phase whereas with s- (sz-) the later development. In the central Volga Bulgar dialect, the č́- retained reflected in the epitaphs, but there existed another dialect where the č́>ś- spirantization was completed, which can be the antecedent of Chuvash. The č->(č́-)>ś- is a parallel process. The -VyV->-VvV- and -Vy>V changes occurred in Volga Bulgar period (tenth-thirteenth cc.). The sā->*s(i̭a-)>ša- and *si/ï->ši/ï- changes can be dated to the Oguric period reflected in the loans in Hungarian. The b survived in most cases until the Mongol invasion and only after it changed into p in Chuvash. The initial b- became m- in nasal environment and it became -v- in intervocalic position. The spirantization g/ġ>γ was general in Oguric period. The further development of γ reflected territorial distribution. The γ>0 change in consonantal environment, intervocalic and final positions took place in one area, whereas the γ>w change appeared in other territory. Then the w was either vocalized (ṷ/ṷ̈) or became v. The k phoneme had front and back allophones (k and q) showing different changes. The initial k- persisted and the medial and final k (-k-, -k) in most cases did not change, but there were territories where secondary voicing occurred (k>g) and then spirantization (g>γ). The q became χ in the late Oguric period reflected in Hungarian hajó ‘boat’, homok ‘sand’, harang ’bell’ and the Chuvash preserved the χ. There are four examples of the change q>y before long illabial vowels. The n was only in medial and final position in Old Turkic and remained unchanged generally. The final n>m was restricted to one region of WOT Oguric before the migration of Bulgar tribes to the Volga region. Both variants survived in the dialects of the Volga Bulgars and Chuvash itself reflects both phenomena. The η can be only medial and final in Old Turkic and there are two possible outcomes: 1. η>n(>m); 2. η>γ(>0). The ń occurred similarly in medial and final position in Turkic, and it turned into ń>n or ń> y. The medial -d- remained unchanged during the Oguric period, and only in the later phase did it begin spirantisation -d->-δ- (Hung. túzok ‘bustard’, búza ‘wheat’). The -δ- became into -z->-r- in the Volga region between the tenth and thirteenth centuries, but -δ- in words with r developed to -y-. The t in all positions persisted in WOT. In Volga Bulgar, the initial and medial ti > či change took place. Agyagási concluded that rhotacism and lambdacism might have persisted since Proto-Turkic period (before the second century AD) in r-Turkic languages (WOT, Middle Chuvash and Chuvash). The WOT period is divided into two sub-periods: Oguric, i.e. languages spoken in the Eastern European steppe between the fifth and tenth centuries (the source of this reconstruction is Turkic loans in Hungarian) and the Volga Bulgar spoken in the Volga–Kama region between the tenth and thirteenth centuries. Innovations in WOT had global effects in both sub-periods (si->ši), while other innovations began only in the Volga Bulgar period (-d->-δ->-z->-r-). There are different possibilities for the regional changes in Oguric: they remained unchanged in Volga Bulgar or were the starting point for regional divisions within Volga Bulgar. Finally, one regional variant of Oguric continued in Volga Bulgar. Most changes in Oguric also occurred in Volga Bulgar, but the change of y->(ǰ-)>č́-and that of y-> (ǰ->č́-)>ś- divided the Volga Bulgar two regional variants.

The third chapter, entitled ‘Oppositions in the WOT/VB vowel system’, discusses first global and regional changes in WOT/Oguric and the WOT/Volga Bulgar vowel system, followed by the dialects of the Volga Bulgar period. In Proto-Turkic, long vowels existed, but there was an overall tendency to shortening. We have no reference for shortening in WOT Oguric, but it is reflected in Chuvash (ā, ō, ū, ī, ē, ǖ). This shortening was disrupted in WOT, and the long vowels were retained, or a process of diphthongization started. During the diphthongization of the illabial long vowels (ā, ī, ē), the i̭-glide appeared first, which turned into consonant y- in the initial position, a development called y-prothesis. The i̭-glide after s- and t- caused palatalization: si>ši and ti>či. The labial long vowels (ō, ū, ö‐, ǖ) similarly went through diphthongization, and the first element turned into ṷ, ṷ̈ and then w>v, in an operation called v-prothesis.

The study of the short vowel system of the Volga Bulgar language made it possible to reconstruct the Volga Bulgar dialects. The short illabial vowel a persisted and the motion a>ȧ began during the Volga Bulgar period, while ȧ>ï occurred in Chuvash. The process a>å occurred in parallel in Volga Bulgar, becoming u in Chuvash. The Turkic o in the first syllable persisted, but in some regions, it became u during the Oguric period. In Volga Bulgar, the o had four regional variants in the first syllable: remaining unchanged, o>u, reduced, o>a. In Chuvash, v-prothesis can be found in place of the Volga Bulgar initial o. The Turkic u persisted in Oguric and in one region of the Volga Bulgar territory, and it was reduced in another territory. The v-prothesis appeared in Chuvash before the initial Volga Bulgar u. The Turkic velar ï was preserved in Oguric and in one region of Volga Bulgaria, and it became reduced reflected in loans into Proto-Permian. Toward the end of Old Turkic period the opposition i : ï disappeared and only i remained causing change in vowel harmony di- and polysyllabic words. It was represented in Chuvash as ě. The secondary y-prothesis appeared in Volga Bulgar and Chuvash before ï in initial position. The Turkic ä had the allophones of close ė in Oguric. The Volga Bulgar loans in Proto-Permian reflected both allophones and the change ė>i also appeared. The reduction of ė is another territorial variant in Volga Bulgar. In the Volga Bulgar dialect, which the Chuvash developed from had also a stabile allophonic distribution. The changes ä>a and ė>i occurred in similar proportion in Chuvash. The Turkic ö turned into ü in Volga Bulgar, but some sporadic cases it remained unchanged. In initial position the ö and ü and represented as vě in Chuvash. The Turkic ü remained in larger territory and it was reduced in a smaller limited region. The Volga Bulgar dialect in the vicinity of Proto-Permian seems to show the sign of reduction process (ü>ü̆). The v-prothesis in initial position is represented in Chuvash. The Turkic i remained unchanged in West Old Turkic its reduction started in Middle Chuvash period. The y-prothesis appeared in the end of the Volga Bulgar period in initial position and persisted in Chuvash.

After the break-up of the Proto-Turkic unity, r-Turkic had four isoglosses (z>r, š>l, -d->-δ-, y>ǰ), all of which can be located in South Siberia. Oguric-speaking tribes arrived in Eastern Europe in the fifth century, WOT Oguric became the dominant language in the steppe regions of Eastern Europe until the tenth to eleventh centuries. Most consonant changes described in WOT occurred during the Oguric period (fifth to tenth centuries). The traces of territorial variation are reflected in the following changes, γ>0 ∼.γ>w; n>n ∼ n>m; η>n ∼ η>γ; t>t ∼ t(i)>š. Here ǰ and č were preserved, or spirantisation occurred. The existence of these dialects is not to be doubted, but their exact locations are hard to define.

The Volga Bulgars established their domains in the Volga–Kama region at the end of the ninth century. Turkic speakers in this area inherited the regional variants of the former period, but their territory became more compact. The linguistic changes that occurred were largely in vocalism. Accordingly, Agyagási reconstructed three dialects in Volga Bulgar in the tenth to thirteenth centuries:

1. 1.VB₁ is reflected by the loanwords in Proto-Permian and ancient Votyak (Udmurt) (pp. 162–168). The first-syllable vowels in VB₁ featured the following changes: a>å, e>i, o>u. Here, ö and ü coincided, and i, u, ü were reduced. In the second syllable, u, ü, i, ï remained, and only delabialisation occurred. There were characteristic changes in consonants as well: č>ś, ǰ>ś, si>ši, ŋ>m, q>χ, g>γ>0.
2. 2.VB₂ can be identified from data from Volga Bulgar epitaphs (thirteenth to fourteenth centuries) and loans as substratum elements in Tatar, Bashkir and Middle Chuvash following the Mongol invasion (pp. 168–180). The basic characteristics of this dialect are the following: preservation of the ǰ : č, č́ : č, s : š oppositions, the -si>-ši third-person possessive, upper vowels retaining their length, with lower vowels beginning diphthongization, v-prothesis before initial labial vowels, the existence of the allophones ä and e.
3. 3.VB₃ is the antecedent of the Chuvash (pp. 180–183). The long–short vowel opposition began to weaken, and the diphthongization of the remaining long vowels began.

To demonstrate this, I collected and reconstructed the numerals in the Volga Bulgar dialects, presented in the table below:

VB₁ was spoken in a region that was in contact with communities speaking Proto-Permian and Proto-Votyak (Proto-Udmurt) (pp. 161–3). It can be localised to the north of the River Kama. The VB₂ dialect, in which the Volga Bulgar epitaphs (1281–1361) are written, was the central dialect of the Volga Bulgars (p. 168). The population of the Volga Bulgars was concentrated south of the Kama and east of the Volga. The VB₃ dialect was spoken in the northern territory of Volga Bulgaria because it was in connection with Proto-Permian-speaking communities and had no direct contact with the VB₁ dialect (p. 180). A comparison of data from Volga Bulgar archaeological monuments indicates that it was spoken west of the Volga.

After the Mongol invasion, the central dialect VB₂ lost its hegemonic position, and the migrant Kipchaks became politically dominant. The end of the central Volga Bulgar dialect is connected with the onset of the plague, as the last epitaph that reflected this dialect was erected in 1361. The speakers of this dialect were assimilated by the Kipchaks. The VB₁ dialect was likely assimilated at under the Kazan Khanate in the fifteenth to sixteenth centuries. The Chuvash language appeared only after the Mongol invasion, and its closest relative was the VB₃ dialect. Intensive Chuvash–Mari contacts began only after the Mongol invasion, during the second half of the thirteenth century.

The fourth chapter discusses changes in the Middle Chuvash period (the thirteenth to eighteenth centuries) (pp. 185–243). Two basic tendencies appeared in the consonantal system: secondary voicing in intervocalic position or after liquids and sonorants and positional softening of the consonants. The latter palatalization tendency appeared only after the Mongol invasion and can be traced in changes ń>y, č́>č and the effect of i̭-glide. After the fall of Kazan in 1552, Russian settlers appeared in the territory of the Chuvash community in significant numbers, and language contacts and later bilingualism reinforced the softening process.

In the vowel system, the reduction of close vowels, the closing of the open vowels and the rearrangement of front vowel harmony were the main tendencies. The first two characteristics are areal tendencies in the Volga region, encompassing the Chuvash, Mari, Tatar and Bashkir languages. It is worth noting that the reduction of vowels in the first syllable did occur in VB_1, but there was no trace of that reduction in VB₃, the antecedent of Chuvash. The reduction occurred in the successor of VB, i.e. Middle Chuvash, only after the Mongol invasion. The source of vowel reduction must have been Mari, but the Mari language community was not identical with the language described as being spoken by the Cheremis in the historical sources before the thirteenth century in the neighbourhood of Volga Bulgaria. Due to the Mongol invasion, the Mari-speaking people moved to the territory of the Volga–Vetluga–Vyatka from the vicinity of Permic-speaking groups. They came into close contact with the population speaking VB₃. Reduced vowels were present in Mari (Proto-Mari), and as the prestige hierarchy came to an end after the fall of the Volga Bulgar state, the interaction between the two languages was intensive, and the Mari reduction was copied in Chuvash.

The Early Middle Chuvash vowel system produced the following changes: ö‐ > ō > å and the phonemicisation of the reduced vowels in monosyllabic words and in the second syllable of bi-syllabic words (i>ĭ, ï>ï̌, u>ŭ, ü>ü̆). The latter process led to the change of accentual relation in Chuvash. In general, in Turkic languages, the accent fell on the final syllable. As second-syllable vowels became reduced, the accent was shifted to an earlier non-reduced vowel in the first syllable.

There was a special group of loanwords in Middle Chuvash taken from groups speaking VB₁ and VB₂ who may have joined the antecedents of the Chuvash after the Mongol invasion or the Kipchak migrations to the Volga region. Agyagási lists words from these dialects (pp. 166–168; 206, 230–232) and labels them the adstratum. Chuvash ethnogenesis was complex. They first appeared in written sources in the first half of the sixteenth century (Kappeler 2016, 41–44). From a linguistic point of view, VB₃ played the dominant role, with adstratum from VB₁ and VB₂. It was influenced by Mari dialects, often in the form of bilingualism. Later study should take the effect of local substratum language(s) into consideration (pp. 218–219).

The basic tendency of late Middle Chuvash vowel system is the closing of the open vowels (å>o, ȧ>ï, e>i), and the ä>a change. Agyagási reconstructs the vowel systems of the two dialects of Modern Chuvash: Viryal and Anatri.

Agyagási emphasizes that the use of the classical comparative method and its family-tree model can only be adopted along with the use of areal and contact linguistic studies to understand the complexity of Chuvash language history (pp. 245–246).

The Appendix contains two treatises (pp. 247–298). The first, ‘The Cheremis in the Volga region’, discusses the problems of the Cheremis habitat before and after the Mongol invasion. From a letter of the Khazar ruler Joseph (tenth century) and the Russian Primary Chronicle (eleventh century), Agyagási concludes that the ethnonym Cheremis denoted a population living in the middle Volga region whose ethnic composition and language cannot be identified. They must have been assimilated similarly to the Muroma, Merya and Chud. There are some traces of Baltic-speaking elements present among them. Their territory was then occupied by Mari- and VB₃-speaking communities following the Mongol invasion. In the sixteenth century, under the name of Cheremis, three languages were spoken in the western territory of Khazan Khanate: Mari, Chuvash, and an unidentified language that later disappeared. The last part presents an analysis of the vocalism of Late Proto-Mari.

This volume contains pertinent references (pp. 299–320) which is complete bibliography of Chuvash language history and indices of Ancient Hungarian, Ancient Votyak (Udmurt), Arabic, Bashkir, Chuvash, Kazan-Tatar, Mari dialects, Middle Mongol, Middle Russian, Middle Tatar, Mishar Tatar, Mordvinian, New Persian, Old Russian, Proto-Mari, Proto-Permian and West Baltic words (pp. 323–333).

Agyagási's work has brought about a fundamental breakthrough in the differentiation of the three Volga Bulgar dialects and the study of Chuvash–Mari contacts from a linguistic and historical point of view. This publication marks a significant milestone in the language history of r-Turkic languages and will prove a firm base for further developments in Chuvash studies.