Choosing the Right Case Ending

Suppose you have already decided that you want an ablative, because you want to say "from". You are not finished. The ablative has four written forms, –аас, –оос, –ээс and –өөс, and the word in front of them decides which one you write. Канад takes Канадаас. хот takes хотоос. гэр takes гэрээс. хөдөө takes хөдөөнөөс, with a consonant appearing out of nowhere. Four words, four different shapes, one meaning.

This is the mechanical half of the Mongolian case system, and it is good news: unlike the question of which case to use, this half has rules. Two of them, crossed. Most learners get into trouble because they are told only one of the two.

The two things to look at

Before you attach anything to a Mongolian noun, you look at two features of that noun.

• Its vowel class. Mongolian words belong to one of two vowel sets, and the vowel inside the ending has to match. This is what decides between –аас and –ээс.
• Its final segment. Is the last letter a consonant, and which one? Is it a vowel, and is that vowel short, long, or part of a diphthong? This is what decides between –д and –т, and whether a linking letter has to be inserted.

Some cases are settled by the first feature alone. Some are settled by the second alone. Two cases need both. Knowing which kind of case you are dealing with is most of the skill.

Step one: the vowel class

How a word's class is read off its vowels is taught on the page about vowel harmony, and the grid of endings that the class then selects is on the page that holds the four-form suffix table. This page takes both as settled and uses one thing from them: the word's controlling vowel. For ном it is о, so the ending is built on о and you write номоос rather than номаас. For мөнгө it is ө, so мөнгөөр rather than мөнгээр. For хичээл it is э, and for салхи it is а, because и does not count. That last point is the one to carry over here, since almost every ending below depends on it.

Step two: the last letter

Sort the word into one of five end-groups. You will use the same five groups for every case.

1. Ends in a plain consonant: ном, хүн, ээж, багш, мод, зав.
2. Ends in г or р: гэр, тэрэг, Улаанбаатар, зориг.
3. Ends in д, т, ц, с, х: хот, Канад, онгоц, улс, ах.
4. Ends in a long vowel or a diphthong: хөдөө, ширээ, нохой, гахай, орой.
5. Ends in и, й or a soft sign: такси, салхи, ой, сургууль, морь.

The three cases the vowel class settles on its own

For the ablative, the instrumental and the comitative, the final consonant is irrelevant. Find the controlling vowel, take the matching column, done.

Look hard at the bottom right cell. The comitative has only three forms, not four: there is no ending in ө, and a word like өрөө (room), whose vowel is ө, still takes –тэй. This is not a typographical slip in the method; it is how the ending behaves, and it is one of a short list of places where vowel harmony does not deliver what you expect. The page on the exceptions to vowel harmony collects all of them.

Two mechanical repairs happen in this group when the word ends in a vowel. Before the ablative, a long vowel takes a linking н: хөдөө becomes хөдөөнөөс, not a string of four ө. Before the instrumental, a long vowel or an и or й takes a linking г: хөдөөгөөр, таксигаар, ойгоор. These two linking letters are part of how Mongolian words are built rather than part of the case system, and they are explained on the page about word structure.

The case the last letter settles on its own

The dative-locative has one ending with no vowel of its own and two shapes, –д and –т, and here the vowel class is irrelevant. What matters is the end-group.

The linking vowel in the third row harmonises like any other vowel: а in Канадад, о in хотод. And a small set of very common nouns takes a linking vowel even though its final consonant is not in that list — the method writes ном with the dative-locative as номонд, where the five groups above would have predicted номд. Dictionaries list номд as well. This is the one corner of the case system where a short list has to be learned rather than derived, and pretending otherwise would leave you wrong in front of a Mongolian speaker.

The accusative: both criteria at once

The accusative has three endings, and you need the end-group first and the vowel class second.

• After a long vowel or a diphthong, and in loanwords ending in a vowel, write a bare –г: ширээг, нохойг, киног. No vowel of its own, so no harmony question.
• After a consonant, when the controlling vowel is а, о or у, write –ыг: номыг, уулыг, гарыг, хотыг.
• After a consonant, when the controlling vowel is э, и, ө or ү, write –ийг: ээжийг, хүнийг, багшийг, гэрийг, салхийг.

Note that the accusative is not a four-way choice. It distinguishes only two vowels, ы against ий, so there is no separate form for о and none for ө: ном gives номыг, not номоыг. The same two-way split governs the genitive, and it is the reason the ablative and the accusative feel like they belong to different systems. One consequence has to be said plainly, because it looks like a contradiction of step one: for these two cases alone, a written и does count, and it counts as a front vowel. салхи behaves as a back-class word for the ablative and the instrumental, but the accusative the method gives for it is салхийг, not салхыг.

One wrinkle. A few native words ending in a short vowel drop that vowel instead of taking a bare –г: the method gives чоно (wolf) with the accusative as чоныг. Loanwords such as кино keep their vowel and take –г. When in doubt, a short final vowel is the unstable one.

The genitive: both criteria, and some memory

Here is where a decision tree stops being a complete answer, and it is better to say so than to sell you a rule that breaks. The method teaches the genitive through examples and does not state a selection rule for it at all. What follows is a set of landmarks drawn from those examples — reliable enough to write with, but not a law, and the genitive keeps a residue you will simply have to remember word by word.

• After a consonant, controlling vowel а, о or у: –ын. номын, хотын, малын, ахын, гарын, улсын.
• After a consonant, controlling vowel э, и, ө or ү: –ийн. гэрийн, хичээлийн, жилийн, дэлгүүрийн, багшийн, сургуулийн.
• A substantial group takes –ны or –ний instead. автобусны, онгоцны, цайны, хурганы, юуны, таксиний, хөдөөний, сүүний, хүнсний, and хэлний. Compare жилийн with хэлний: both words end in л, both are front-class, and they take different endings. No tree gets you from one to the other. These are learned.
• After –ай or –ой, a bare –н. оройн хоол (the evening meal), гахайн мах (pork).

Words ending in a long vowel or a diphthong other than –ай and –ой are not covered by the method's examples at all; reference grammars give –гийн there. The page on the genitive handles that form, and flags it as coming from outside the method.

Four things that happen to the word itself

Three of these you have already met in passing. They are listed together because each one makes a word look unrecognisable, and a learner who does not expect them concludes that Mongolian is irregular when it is not.

A short vowel drops out

When a word of two syllables has a short vowel in the second one, that vowel usually disappears before an ending: өнөөдөр gives өнөөдрийн, намар gives намрын, хүүхэд gives хүүхдийн, ажил gives ажлыг, тэрэг gives тэргээр. The word structure page owns this.

A linking consonant appears

н before the ablative and г before the instrumental, after a long vowel: хөдөөнөөс, хөдөөгөөр. Also on the word structure page.

An unstable н

A class of nouns ends in an н that does not always stay. малчин (herder) keeps it in most cases — малчинд, малчинтай — but the method writes the genitive as малчны. The same class loses the н in the plural, which the page on the plural explains.

Only the last word of a group is inflected

их сургуулиас, галт тэргээр, зочид буудалд. Decide the ending from the last word of the group and ignore the others. The overview page on the seven cases treats this as one of the reflexes that hold everywhere.

Pronouns are outside the tree

Do not run this tree on би, чи or та. The personal pronouns carry their own stems, so neither their final letter nor their vowels predict anything: the ablative of чи is чамаас. They are looked up rather than derived, and the fact that they escape this tree is exactly why they have a page of their own — the page on pronouns and possessives, which holds the whole paradigm. Everything else in the language goes through the tree.

The tree run on four words

Four worked examples, in the order you would actually think.

• хот, ablative. Controlling vowel о, so the о column. Final letter irrelevant for this case. Result: хотоос.
• хот, dative-locative. Vowel class irrelevant. Final letter т, so end-group three: linking vowel, harmonised to о, then –д. Result: хотод.
• хөдөө, instrumental. Controlling vowel ө, so –өөр. Ends in a long vowel, so a linking г. Result: хөдөөгөөр.
• багш, accusative. Ends in a consonant, controlling vowel а — but the accusative splits only two ways, and багш behaves as a front-class word here. Result: багшийг, which is the form the method gives, and a reminder that the accusative and the genitive do not follow the four-column grid.

Run the tree out loud a few dozen times and it stops being a tree. What remains conscious, long after the rest has gone automatic, is the genitive — which is exactly why it is worth knowing now that the genitive is the part you memorise, rather than discovering it later and assuming you have misunderstood the system.