4Grammar and explanations
"Must": –х + ёстой
For a firm obligation, such as a rule, a law or a duty, put the verb in its –х form and add ёстой. Like хэрэгтэй, ёстой is not a verb but a word in –той: it is built on ёс "custom, rule", so it means something like "as the rule says".
Та энэ маягтыг бөглөх ёстой.you this form-ACC fill.in-PART must"You must fill in this form."
Та хураамж төлөх ёстой.you fee pay-PART must"You must pay a fee."
Би виз сунгах ёстой.I visa extend-PART must"I must extend my visa."
Хүүхэд сургуульд явах ёстой.child school-DAT go-PART must"Children must go to school."
ёстой or хэрэгтэй?
Both can translate "have to". The difference is where the obligation comes from.
| Pattern | Meaning | Example |
|---|
| –х ёстой | a rule or a duty imposed from outside | Та хураамж төлөх ёстой. |
| –х хэрэгтэй | a practical need | Бид эрт явах хэрэгтэй. |
An official tells you what you ёстой do; a friend tells you what you хэрэгтэй do. That is why Limba says Би виз сунгах хэрэгтэй "I need to extend my visa", and the official answers with ёстой.
Questions
With a question word: Хэзээ ирэх ёстой вэ? "When must I come?" For a yes/no question, remember that ёстой ends in a diphthong and has back vowels, so the particle is юу: Би маргааш ирэх ёстой юу? "Must I come tomorrow?"
"Must not"
For "you must not", Mongolians usually use the construction of lesson 65: Энд зураг авч болохгүй. "You mustn't take photos here." You will also read –х ёсгүй, the negative of ёстой, in rules and notices.
Go deeper in the grammar guide: Can, must, want, like · Wanting and needing
5Good to know
ёс "custom, rule" is a useful little word. Монгол ёсоор means "the Mongolian way", and ёс заншил means "customs and traditions". Notice its vowel: ё belongs with the back vowels, so the endings are back too, as in ёстой, ёсоор and ёсны, even though the letter looks like е.