Must and Need: Должен, Надо, Нужно | Russian Grammar

To say "I must" and "I need to" in Russian, you reach for words that sit in opposite grammatical worlds. До́лжен behaves like an adjective and clings to a nominative subject ("I am obliged"). На́до and ну́жно are impersonal — there is no subject at all, and the person is demoted to the dative ("to-me [it is] necessary"). Get the case wrong and the sentence collapses. This page lays the two patterns side by side, adds the third twist — ну́жен agreeing with the thing you need — and shows how all of them form the past and future.

до́лжен — obligation with a nominative subject

до́лжен means "must / have to / should / am obliged to". Grammatically it is a short adjective, so it agrees with the subject in gender and number, exactly like рад (glad) or гото́в (ready). The subject stays in the nominative — this is the one obligation word that keeps an ordinary "I / she / they" subject.

Subject	Form	Example
masculine (он, я m.)	до́лжен	Я до́лжен идти́.
feminine (она́, я f.)	должна́	Она́ должна́ рабо́тать.
neuter (оно́)	должно́	Всё должно́ быть гото́во.
plural (они́, мы, вы)	должны́	Вы должны́ знать.

It is followed by an infinitive (the thing you must do).

Я до́лжен идти́, меня́ ждут.

I have to go, they're waiting for me. (masculine subject → до́лжен)

Она́ должна́ зако́нчить отчёт сего́дня.

She has to finish the report today. (feminine subject она́ → должна́)

Вы должны́ заполни́ть э́ту фо́рму.

You must fill in this form. (plural/polite вы → должны́)

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Because до́лжен agrees with the subject, you must commit to the speaker's gender even for "I": a man says Я до́лжен, a woman says Я должна́. There is no neutral form for a first-person "I must". This feels alien to English speakers, where must never changes shape.

до́лжен can also mean "owe"

The same word до́лжен, with a person in the dative and a sum, means literally owe money. Context (a number, no infinitive) tells the two apart:

Ты мне до́лжен три́ста рубле́й.

You owe me three hundred rubles. (дать-style debt: до́лжен + dative person + sum, no infinitive)

на́до / ну́жно — impersonal necessity with the dative

на́до and ну́жно both mean "(one) needs to / it's necessary to". They are impersonal: there is no nominative subject, the word never changes form, and the person who has the need goes into the dative. The two are near-synonyms — ну́жно is slightly more neutral, на́до a touch more colloquial — and in everyday speech they're interchangeable.

Мне на́до идти́.

I need to go. (no 'I' subject; я → dative мне + на́до + infinitive)

Нам ну́жно купи́ть хлеб и молоко́.

We need to buy bread and milk. (мы → dative нам + ну́жно + infinitive)

Тебе́ на́до отдохну́ть.

You need to rest. (ты → dative тебе́)

The dative pronouns you'll use constantly: мне (to me), тебе́ (to you), ему́ (to him), ей (to her), нам (to us), вам (to you pl./formal), им (to them). The full pattern of dative experiencers — including мо́жно, нельзя́, пора́, and the evaluative adverbs — is drilled on dative with impersonal modals and the broader dative subject page.

до́лжен vs на́до — the core contrast

The same English "she must / she needs to work" lands in two completely different grammars:

Pattern	Subject case	Example
до́лжен (agreeing adjective)	nominative	Она́ должна́ рабо́тать.
на́до / ну́жно (impersonal)	dative	Ей на́до рабо́тать.

There's a faint nuance: до́лжен leans toward a duty or obligation (something expected of you, a commitment), while на́до/ну́жно leans toward a practical necessity (it's required by the situation). But the overlap is huge, and both are everyday. What you cannot do is mix the cases — Она́ должна́ needs nominative она́, Ей на́до needs dative ей.

Я до́лжен извини́ться — э́то моя́ вина́.

I must apologize — it's my fault. (до́лжен leans 'moral obligation'; nominative я)

Мне на́до купи́ть но́вые ту́фли.

I need to buy new shoes. (на́до leans 'practical need'; dative мне)

ну́жен / нужна́ / ну́жно / нужны́ — needing a thing

Everything above was about needing to do something (an infinitive). To say you need a thing — a noun — Russian flips the grammar one more time. It uses the short adjective ну́жен / нужна́ / ну́жно / нужны́, which agrees with the needed thing (the thing is the nominative subject!), while the needer stays in the dative.

Needed thing	Form	Example
masculine	ну́жен	Мне ну́жен слова́рь.
feminine	нужна́	Мне нужна́ кни́га.
neuter	ну́жно	Мне ну́жно вре́мя.
plural	нужны́	Ему́ нужны́ де́ньги.

Мне нужна́ твоя́ по́мощь.

I need your help. (по́мощь is feminine → нужна́; needer я → dative мне)

Ему́ нужны́ де́ньги на ремо́нт.

He needs money for the repairs. (де́ньги is plural → нужны́; он → dative ему́)

Мне нужны́ очки́ для чте́ния.

I need reading glasses. (очки́ is plural → нужны́)

To English ears this feels backwards: in I need glasses, "I" is the subject and "glasses" the object. Russian makes glasses the subject ("glasses are necessary to me") and the agreement tracks them — hence the plural нужны́ for очки́ and де́ньги. The needer is just a dative bystander.

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Don't confuse the two нужн- patterns. ну́жно + infinitive is frozen (Мне ну́жно идти́). ну́жен / нужна́ / ну́жно / нужны́ + noun agrees with the noun (Мне нужна́ кни́га). If a noun follows, make the word agree with it; if an infinitive follows, leave it as ну́жно.

Past and future

до́лжен forms its past with the verb быть agreeing with the subject — был / была́ / бы́ло / бы́ли — placed after до́лжен:

Я до́лжен был уйти́ ра́ньше.

I had to leave earlier. (masculine: до́лжен был; subject я nominative)

Она́ должна́ была́ позвони́ть.

She was supposed to call. (feminine: должна́ была́)

The future is до́лжен бу́ду / бу́дешь…: Я до́лжен бу́ду рабо́тать — "I'll have to work."

на́до / ну́жно, being impersonal, insert the frozen neuter бы́ло (past) and бу́дет (future) — never agreeing with anyone, because there is no subject:

Мне на́до бы́ло позвони́ть, но я забы́л.

I needed to call but forgot. (impersonal past: frozen neuter бы́ло — never была́, even for a woman)

Нам ну́жно бу́дет встре́титься за́втра.

We'll need to meet tomorrow. (impersonal future: frozen neuter бу́дет)

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This is the deepest past-tense trap. With до́лжен the быть-verb agrees (Она́ должна́ была́). With на́до/ну́жно the быть-verb is frozen neuter (Ей на́до бы́ло), because there's no subject to agree with — never *Ей на́до была́.

A short note on the dative's other jobs

The same dative-experiencer logic powers more than necessity. Age (Мне два́дцать лет — "I'm twenty"), feelings (Ей хо́лодно — "she's cold"), and time-of-day statements all put the person in the dative. The age-and-time uses are on dative for age and time, and the wider obligation vocabulary — сле́дует, обя́зан, прихо́дится — is mapped on the obligation spectrum.

Common Mistakes

❌ Я на́до идти́.

Incorrect — на́до is impersonal; the person is dative. 'I need to go' is Мне на́до идти́.

✅ Мне на́до идти́.

I need to go. (dative мне + на́до)

❌ Мне до́лжен рабо́тать.

Incorrect — до́лжен keeps a nominative subject and agrees with it. 'I must work' is Я до́лжен / должна́ рабо́тать.

✅ Я до́лжен рабо́тать.

I must work. (nominative я + agreeing до́лжен)

❌ Ей на́до была́ позвони́ть.

Incorrect — на́до is impersonal, so the past is frozen neuter бы́ло, never agreeing with 'her'.

✅ Ей на́до бы́ло позвони́ть.

She had to call. (dative ей + frozen neuter бы́ло)

❌ Мне ну́жно кни́га.

Incorrect — for a needed THING the word agrees with it: кни́га is feminine → нужна́.

✅ Мне нужна́ кни́га.

I need a book. (feminine кни́га → нужна́; needer dative мне)

❌ Я должен очки́.

Incorrect — needing a thing isn't должен (that's 'owe'); use ну́жен agreeing with the thing. Очки́ is plural → нужны́.

✅ Мне нужны́ очки́.

I need glasses. (plural очки́ → нужны́; dative мне)

Key Takeaways

до́лжен / должна́ / должно́ / должны́ — short adjective, nominative subject, agrees in gender/number: Я до́лжен идти́, Она́ должна́ рабо́тать, Вы должны́ знать. Also means "owe" with a dative person and a sum.
на́до / ну́жно — impersonal, dative experiencer, no subject, frozen form: Мне на́до идти́, Нам ну́жно купи́ть хлеб.
ну́жен / нужна́ / ну́жно / нужны́ — needing a thing: agrees with the needed noun (the nominative subject), needer stays dative: Мне нужна́ кни́га, Ему́ нужны́ де́ньги.
Past/future: до́лжен takes an agreeing быть (до́лжен был, должна́ была́); на́до/ну́жно take a frozen neuter бы́ло / бу́дет (Ей на́до бы́ло — never была́).
The English instinct is one nominative "I" for every modal. Russian forces the case to match the construction: nominative for до́лжен, dative for на́до/ну́жно, and agreement-with-the-thing for ну́жен.

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