Case

All three languages have the basic case paradigm of the Common Mongolic type comprising an unmarked form (labeled as “nominative” but functioning also as direct object in the frame of differential object marking) and six suffixally-marked cases: genitive, accusative, dative, ablative, instrumental, and possessive. In contrast to Khalkha and Buryat, Kalmyk preserves the primary comitative case form in -lA; it also has a grammaticalized directive, -Ur, and a rare case-like form -cA labelled as terminative. There is an additional marker whose status in the case paradigm is ambiguous: the proprietive in -tAi, building a functional pair with the privative in -güi/-go (cf. Kl. gergn ‘woman/wife’, gerg-tä ‘married/with a wife’, gergn-go ‘unmarried/without a wife’) can be presented either as a derivation suffix or as a marker of ‘possessive case’ (note that its negative counterpart is not treated this way in the Mongolic studies, though in grammars of other languages, privative/caritive cases are not uncommon).
In all three languages, the most case markers have allomorphs after the regular Common Mongolic patterns with the basic form used after:

C: consonant stems
V: short-vowel stems
N: the nasal stems
Ng: velar-nasal stems
VV: long-vowel stems where the connective consonant g/h is required
Vi: diphthong stems where the connective consonant g/h is required
O: obstruent stems (special suffix variants in the dative)
CVV: double-vowel-stem which are synchronically monosyllabic

Table: Case system of the Khalkha-Mongolian, Buryat and Kalmyk (based on the data of Svantesson 2003, Skribnik 2003, Bläsing 2003)

language	stem	case
language	stem	genitive	accusative	dative	ablative	instrumental	possessive	comitative	direktive	terminative
Khalkha	C	-ijn/-yn	-ijg/-yg	-d	-AAs	-AAr	---	-tAj	-rUU/ -lUU	---
	O			-t			---			---
	V		-g							---
	N	-ij/-y					---			---
	Ng	-g-ijn	-g-ijg/-yg		-g-AAs	-gAAr	---			---
	Vi	-n					---			---
Buryat	V	-iin	-iiyi	-dA	-hAA	-AAr	-tAi	---	---	---
	C	-Ai						---	---	---
	O			-tA				---	---	---
	Vi	-n	-yi			-g-AAr		---	---	---
	VV	-g-Ai						---	---	---
	Ng		-g-iiyi		-g-hAA			---	---	---
Kalmyk	V/C	-in	-ig	-d	-As	-Ar	-tA	-lA	-Ur	-cA
	O			-t
	N	-(n)Ä
	VV	-n	-g		-h-As	-h-Ar			-h-Ur
	CVV	-h-in

Syntactic cases are nominative, genitive, accusative. The unmarked nominal stem is considered a nominative and is used as the citation form in the dictionaries. Syntactically, the nominative is the form of the subject and the direct indefinite (unspecified) object, while the accusative indicates the direct definite (specified) object. The genitive serves to express various types of adnominal attributes and to mark the primary actants of deverbal nouns.

All other cases function either as semantic, or as both syntactic and semantic. The dative (dative-locative) and the ablative are local cases encoding spatial and temporal meanings. The dative can express the addressee and recipient and indicates a positive emotional reaction, while the ablative marks the source and encodes the stimulus of a negative emotional reaction. The dative can also mark the actor in passive constructions, and the ablative the standard of comparison. The instrumental of inanimate nouns codes various circumstances such as tool, means, payment, material, time, period, cause etc. The instrumental of animate nouns has a comitative meaning, coding the active participation of a second participant. The possessive, like the instrumental in adverbial use, indicates simple accompaniment. Parallel to the possessive -tA, Kalmyk preserves the primary comitative -lA.

The case markers attached to participles as predicates of dependent clauses function as connectors and express both syntactic and semantic relationship between two clauses. Participial constructions with case markers are highly idiomatic; not every participial form is freely combinable with any case marker; they are easily grammaticalized into converbs (cf. Janhunen’s term ‘quasiconverb’, 2003: 26) (s. more under ‘Participles’ and ‘Converbs’).