Three obligation words, three different grammars:
- до́лжен / должна́ / должно́ / должны́ — a short adjective; the doer is the nominative subject and the word agrees with it
- на́до / ну́жно — impersonal; the doer is in the dative, the word never changes
- ну́жен / нужна́ / ну́жно / нужны́ — agrees with the thing needed, with the needer in the dative
This is one of the highest-value pages in the early course, because English flattens three distinct Russian patterns into "must / have to / need." The trap is grammatical, not lexical: до́лжен behaves like an adjective (it agrees with the person who must act), while на́до / ну́жно are impersonal — there is no nominative subject at all, and the person who must act sits in the dative. A third member, ну́жен / нужна́…, looks like ну́жно but agrees with the thing you need. Get the grammar of the subject right and these become easy; mix them up and every sentence sounds wrong. Stress is marked on every multi-syllable form.
The core contrast at a glance
| до́лжен (must / be obliged) | на́до / ну́жно (need to / have to) | ну́жен (need [a thing]) | |
|---|---|---|---|
| Type | short adjective | impersonal predicate | short adjective |
| Who must act? | nominative subject | dative (no subject) | dative (the needer) |
| Agrees with… | the person (subject) | nothing — invariable | the thing needed |
| Followed by… | infinitive | infinitive | a noun (the thing) |
| Example | Я до́лжен идти́. | Мне на́до идти́. | Мне нужна́ по́мощь. |
The key move: до́лжен keeps a real subject in the nominative (я, он, она́, мы), so you choose the form by that subject's gender and number. на́до / ну́жно throw the subject into the dative and stay frozen. ну́жен is the odd one out — it agrees not with the person but with the object of need.
1. До́лжен — agrees with the subject (nominative)
до́лжен is a short-form adjective meaning "obliged, must, ought to, owe." Like all short adjectives, it agrees with its subject in gender and number, and the subject is in the nominative. After it comes an infinitive (the action you must do). Stress: feminine, neuter, and plural are end-stressed (должна́, должно́, должны́), masculine is до́лжен.
| Subject | form | example |
|---|---|---|
| masculine (он, я m.) | до́лжен | Он до́лжен рабо́тать. |
| feminine (она́, я f.) | должна́ | Она́ должна́ рабо́тать. |
| neuter (оно́) | должно́ | Всё должно́ рабо́тать. |
| plural (мы, вы, они́) | должны́ | Мы должны́ рабо́тать. |
The sense of до́лжен leans toward personal obligation, duty, or strong necessity — "I must, I am obliged to, I have to." It is also the verb for owing: Ты мне до́лжен ты́сячу рубле́й "You owe me a thousand roubles."
Я должна́ зако́нчить отчёт до пя́тницы.
I (female) have to finish the report by Friday. — должна́ agrees with a female я; nominative subject.
Все студе́нты должны́ сдать рабо́ту во́время.
All students must hand in their work on time. — plural subject → должны́.
Ты до́лжен мне сто рубле́й за такси́.
You owe me a hundred roubles for the taxi. — до́лжен = 'owe' + dative person + accusative sum.
2. На́до / ну́жно — impersonal, with a dative subject
на́до and ну́жно are impersonal predicates: they never change form, there is no nominative subject, and the person who has to act stands in the dative. They are followed by an infinitive. на́до and ну́жно are near-synonyms here ("need to, have to, ought to"); на́до is a touch more colloquial, ну́жно a touch more neutral, but they are interchangeable in most everyday sentences. See the impersonal modals page.
Мне на́до идти́, уже́ по́здно.
I have to go, it's already late. — на́до with dative мне; no nominative subject.
Тебе́ ну́жно отдохну́ть, ты о́чень уста́л.
You need to rest, you're very tired. — ну́жно + dative тебе́ + infinitive.
Нам на́до поговори́ть об э́том серьёзно.
We need to talk about this seriously. — dative нам; на́до stays frozen.
You can drop the dative when the obligation is general ("one has to," "you need to" in the impersonal English sense): Здесь на́до молча́ть "One has to be quiet here."
3. Ну́жен — agrees with the thing needed
When you need a thing (a noun, not an action), Russian uses the short adjective ну́жен, which agrees with that thing — the grammatical subject is the thing needed, and the needer goes in the dative. Literally it is "to-me is-needed help" = "I need help." This pattern catches every English speaker, because in English I am the subject of "need," whereas in Russian the thing is.
| The thing needed | form | example |
|---|---|---|
| masculine noun | ну́жен | Мне ну́жен сове́т. |
| feminine noun | нужна́ | Мне нужна́ по́мощь. |
| neuter noun | ну́жно | Мне ну́жно вре́мя. |
| plural noun | нужны́ | Мне нужны́ де́ньги. |
Note that the neuter form ну́жно is identical to the impersonal ну́жно of section 2 — context tells them apart: ну́жно + infinitive is impersonal ("need to do"), while ну́жно + neuter noun agrees with that noun ("need [a neuter thing]").
Мне нужна́ твоя́ по́мощь, я не справля́юсь.
I need your help, I can't cope. — нужна́ agrees with feminine по́мощь; needer in dative мне.
Ему́ нужны́ но́вые о́чки — э́ти слома́лись.
He needs new glasses — these broke. — plural нужны́ agrees with о́чки; needer ему́ (dative).
Что тебе́ ну́жно для сча́стья?
What do you need to be happy? — ну́жно agrees with the neuter что; needer тебе́.
Past and future
All three drop their tense onto the verb быть. The grammar of each predicate decides how быть agrees.
| PAST | FUTURE | |
|---|---|---|
| до́лжен (agrees w/ subject) | был до́лжен / была́ должна́ / бы́ли должны́ | бу́ду до́лжен / бу́дет должна́ … |
| на́до / ну́жно (impersonal) | на́до бы́ло / ну́жно бы́ло (neuter, frozen) | на́до бу́дет / ну́жно бу́дет |
| ну́жен (agrees w/ thing) | был ну́жен / была́ нужна́ / бы́ли нужны́ | бу́дет ну́жен / бу́дет нужна́ / бу́дут нужны́ |
With на́до / ну́жно, быть stays neuter singular (бы́ло, бу́дет) because the construction is impersonal — Мне на́до бы́ло идти́ "I had to go." With до́лжен and ну́жен, быть agrees with the relevant noun: Она́ была́ должна́…, Мне нужны́ бы́ли де́ньги. A very common future alternative to "will have to" is the impersonal придётся (+ dative + infinitive), which adds a flavour of unwelcome necessity.
Вчера́ мне на́до бы́ло остаться на рабо́те допоздна́.
Yesterday I had to stay late at work. — на́до бы́ло: neuter бы́ло, impersonal past + dative мне.
Она́ была́ должна́ всё объясни́ть, но промолча́ла.
She was supposed to explain everything, but stayed silent. — была́ должна́: быть agrees with она́.
За́втра нам придётся встать о́чень ра́но.
Tomorrow we'll have to get up very early. — придётся + dative нам: the everyday 'will have to'.
Common Mistakes
❌ Мне до́лжен идти́.
Mismatch — до́лжен needs a NOMINATIVE subject it agrees with. With the dative мне, use the impersonal на́до/ну́жно: Мне на́до идти́. Or say Я до́лжен идти́.
✅ Мне на́до идти́. / Я до́лжен идти́.
I have to go.
❌ Я на́до идти́.
Wrong case — на́до is impersonal: the person is DATIVE, not nominative. Use Мне на́до идти́ (or switch to Я до́лжен идти́).
✅ Мне на́до идти́.
I have to go.
❌ Она́ до́лжен рабо́тать.
Agreement error — до́лжен agrees with the subject's gender: a female subject takes должна́.
✅ Она́ должна́ рабо́тать.
She has to work.
❌ Мне ну́жен по́мощь. / Я нужна́ де́ньги.
Agreement error — ну́жен agrees with the THING needed (feminine по́мощь → нужна́; plural де́ньги → нужны́), and the needer is DATIVE (мне).
✅ Мне нужна́ по́мощь. / Мне нужны́ де́ньги.
I need help. / I need money.
❌ Вчера́ мне на́до была́ идти́.
Agreement error — with impersonal на́до, быть stays NEUTER: на́до бы́ло (not была́), regardless of the person.
✅ Вчера́ мне на́до бы́ло идти́.
Yesterday I had to go.
Key Takeaways
- до́лжен / должна́ / должно́ / должны́ — short adjective; nominative subject; agrees with it; + infinitive. Strong personal obligation, and "to owe."
- на́до / ну́жно — impersonal, never change; the person is dative; + infinitive. "Need to / have to."
- ну́жен / нужна́ / ну́жно / нужны́ — short adjective that agrees with the thing needed; the needer is dative; + a noun.
- Past / future ride on быть: impersonal на́до бы́ло / на́до бу́дет (neuter, frozen); до́лжен and ну́жен make быть agree (была́ должна́, бы́ли нужны́). The everyday "will have to" is придётся
- dative.
- Decide by the case of the person: nominative → до́лжен; dative → на́до / ну́жно (action) or ну́жен (thing).
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- Dative with Impersonal Modals (можно, нужно, нельзя, пора)A2 — Russian expresses most modality about people with a frozen pattern: dative person + impersonal word + infinitive. Мне на́до идти́ (I have to go), Вам мо́жно войти́ (you may come in), Ему́ нельзя́ кури́ть (he mustn't smoke), Нам пора́ е́хать (it's time for us to go), Тебе́ тру́дно поня́ть (it's hard for you to understand). Past/future insert frozen neuter бы́ло/бу́дет (Мне на́до бы́ло уйти́). The experiencer is the DATIVE — there's no nominative 'I'. Plus the agreeing ну́жен/нужна́/ну́жно/нужны́ for needing a thing (Мне нужна́ по́мощь, Мне нужны́ де́ньги).
- Expressing 'Have To' and 'Need To': A SummaryA2 — A compact A2 cheat-sheet of the high-frequency ways to say must / need / it's time in Russian. До́лжен agrees with a nominative subject; на́до/ну́жно are impersonal with a dative experiencer; ну́жен agrees with the needed thing; пора́ means 'it's time'. One comparison table, plus past and future.
- Past-Tense Gender and Number AgreementA2 — The Russian past tense agrees with its subject in gender (singular) and number — он чита́л, она́ чита́ла, оно́ чита́ло, они́ чита́ли. The traps: я/ты take the gender of the real speaker or addressee; polite Вы always takes plural -ли even for one person; кто forces masculine and что forces neuter regardless of the real referent. This page works through every agreement target.
- Dative: The Indirect ObjectA2 — The dative's core job is the indirect object — the recipient or beneficiary, answering кому? (to whom?). The frame is subject (nom) + verb + thing (acc) + recipient (dat): Я дал дру́гу кни́гу (I gave my friend a book), Она́ написа́ла письмо́ ма́ме. The trap for English speakers is a closed list of verbs that take the dative where English uses a plain direct object — помога́ть (help), звони́ть (phone), сове́товать (advise), ве́рить (believe), меша́ть (bother), ра́доваться (be glad about) — so 'I help my brother' is Я помога́ю бра́ту (dat), not *брата.
- The Obligation Spectrum: должен, надо, нужно, обязан, приходитсяB2 — English flattens obligation into 'must / have to / should / need to', but Russian spreads it across a graded set that differs in both SYNTAX and FORCE. До́лжен (nominative, personal duty), на́до/ну́жно (dative, practical need), прихо́дится/пришло́сь (dative, unavoidable external compulsion: Мне пришло́сь уйти́), обя́зан (formal obligation), сле́дует (advisable), сто́ит (it's worth). Choosing among them tells the listener WHY the obligation exists.
- Dative Subjects: Feelings, Age, NecessityA2 — In a signature Russian construction the logical subject — the person experiencing a state — stands in the DATIVE, not the nominative, and there is often no nominative subject and no real verb at all. Feelings: Мне хо́лодно (I'm cold), Ему́ ску́чно (he's bored). Age: Мне два́дцать лет (I'm 20). Necessity/permission: Мне на́до идти́ (I have to go), Здесь нельзя́ кури́ть (you can't smoke here). Liking: Мне нра́вится му́зыка (music is pleasing to me — the liked thing is the nominative subject!). The verb, when present, is frozen neuter. This is where English speakers most resist Russian, and mastering it is the gateway to sounding native.