Must / Should: Треба, Мусити, Повинен, Слід | Ukrainian Grammar

English packs "must," "have to," "need to," "should," and "ought to" into a handful of words that all behave the same way grammatically — I is the subject every time. Ukrainian does the opposite: it has four main necessity words and they differ on two axes at once — the grammar they demand and the force they carry. тре́ба is impersonal and wants a dative person; пови́нен is an adjective that agrees with the subject; му́сити is a full verb that conjugates; слід is a bookish impersonal "one ought." Getting this right means choosing not just the word but the whole sentence frame around it. This page lays out each one, ranks them by strength, and untangles the three different negations, which mean three different things.

тре́ба — neutral "need to," impersonal + dative

Тре́ба is the everyday, neutral word for necessity: "need to, have to, one must." It is impersonal — it never changes form — and the person who needs something stands in the dative, exactly as with мо́жна and мені́ хо́лодно. There is no verb "to be" in the present: you say literally "to-me need to-go."

Мені́ тре́ба йти, бо я запі́знююся на по́тяг.

I need to go, because I'm late for the train. (Dative мені́ + impersonal тре́ба + infinitive.)

Тре́ба купи́ти хлі́ба й молока́ — удо́ма нічо́го нема́є.

We need to buy bread and milk — there's nothing at home. (No dative named: a general 'one needs to.')

Не тре́ба хвилюва́тися, усе́ бу́де гара́зд.

There's no need to worry, everything will be fine. (Negated тре́ба = 'no need.')

For past and future, add the neuter form of "to be" — тре́ба було́ "needed to," тре́ба бу́де "will need to" — and the person stays dative throughout:

Мені́ тре́ба було́ подзвони́ти ра́ніше, ви́бач.

I should have / needed to call earlier, sorry. (Past: neuter було́, person still dative.)

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Build the тре́ба sentence in this order: dative person (мені́, тобі́, нам…) + тре́ба + infinitive. There is no nominative "I" — the same experiencer frame you learned for мені́ хо́лодно and мо́жна. See the dative core uses page for the whole pattern.

му́сити — strong compulsion, a conjugating verb

Му́сити is a real verb — it conjugates for person — and it carries the strongest sense of necessity: "must, have to," often under external pressure or unavoidable circumstance. The subject is a normal nominative (я, ти, ми), unlike тре́ба.

Person	Present	English
я	му́шу	I must
ти	му́сиш	you must (sg.)
він / вона́ / воно́	му́сить	he / she / it must
ми	му́симо	we must
ви	му́сите	you must (pl./formal)
вони́	му́сять	they must

Я му́шу працюва́ти в субо́ту — нема́є кому́ мене́ підміни́ти.

I have to work on Saturday — there's no one to cover for me. (Unavoidable external pressure: му́сити.)

Ми му́сили чека́ти дві годи́ни на ре́йс.

We had to wait two hours for the flight. (Past of му́сити: forced by circumstances.)

Ти не му́сиш цьо́го роби́ти, якщо́ не хо́чеш.

You don't have to do this if you don't want to. (Negated му́сити = 'are not obliged to' — see the negation section.)

пови́нен — obligation, an adjective that AGREES

Пови́нен means "ought to, supposed to, must" in the sense of a duty or obligation. Grammatically it is not a verb but a short adjective-like form, and — this is the crucial, error-prone point — it agrees with the subject in gender and number, just like an adjective:

Subject	Form	Example
masculine sg.	пови́нен	він пови́нен
feminine sg.	пови́нна	вона́ пови́нна
neuter sg.	пови́нне	воно́ пови́нне
plural	пови́нні	ми / ви / вони́ пови́нні

So "I should call" is я пови́нен подзвони́ти if a man is speaking but я пови́нна подзвони́ти if a woman is. The form follows the gender of the subject, not of the speaker abstractly — and learners forget this constantly.

Я пови́нен подзвони́ти кліє́нтові до обі́ду.

I have to call the client before lunch. (Male speaker → пови́нен.)

Вона́ пови́нна зна́ти про це пе́ршою.

She ought to know about this first. (Feminine subject → пови́нна.)

Ви пови́нні запо́внити цю фо́рму до кінця́ ти́жня.

You must fill in this form by the end of the week. (Plural / formal → пови́нні.)

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The single most common пови́нен error is failing to agree it: a woman saying я пови́нен instead of я пови́нна, or ми пови́нен instead of ми пови́нні. Treat пови́нен like an adjective — match it to the subject's gender and number every single time.

слід — bookish "one should, ought to"

Слід is impersonal like тре́ба, takes an infinitive, and means "one should / ought to." It is advisory and noticeably more bookish / formal — common in written advice, instructions, and careful speech, less so in casual chat, where тре́ба or пови́нен do the job. An optional dative names who ought to.

Слід зважа́ти на ду́мку інши́х.

One should take others' opinions into account. (Impersonal advisory слід — measured, bookish register.)

Тобі́ слід відпочи́ти — ти ма́єш стомлений ви́гляд.

You ought to rest — you look tired. (Gentle advice with an optional dative тобі́.)

Перш ніж підпи́сувати, слід уважно прочита́ти умо́ви.

Before signing, one should read the terms carefully. (Formal instruction.)

The strength ladder

All four can render an English "must / should," but they sit at different points on a scale of force:

Weakest → Strongest	Word	Sense	Grammar
advisory	слід	one ought to (bookish)	impersonal + infinitive
neutral need	тре́ба	need to / have to	impersonal + dative + inf.
obligation	пови́нен	ought to / supposed to	agrees: пови́нен/пови́нна/пови́нні
compulsion	му́сити	must, have no choice	conjugates: му́шу/му́сиш…

The same English sentence, "I must call her," therefore has three natural flavours that differ in both force and grammar:

Мені́ тре́ба їй подзвони́ти.

I need to call her. (Neutral necessity — тре́ба, dative subject.)

Я пови́нен їй подзвони́ти.

I'm supposed to / ought to call her. (Obligation/duty — пови́нен, agreeing adjective, male speaker.)

Я му́шу їй подзвони́ти.

I must call her — I have no choice. (Strongest compulsion — му́сити, conjugating verb.)

The three negations mean three different things

This is where learners go badly wrong, because in English "you mustn't" and "you don't have to" sound similar but mean opposites. Ukrainian keeps them sharply distinct:

не тре́ба = "there's no need" (the action is unnecessary, but not forbidden);
не мо́жна = "must not, it's forbidden" (a prohibition — note it negates мо́жна "may," covered on the могти́ vs вмі́ти page);
не му́сиш / не пови́нен = "don't have to, aren't obliged to" (the obligation is lifted, the action is optional).

Не тре́ба мене́ зустріча́ти, я дої́ду сам.

There's no need to meet me, I'll get there myself. (Unnecessary — не тре́ба.)

Тут не мо́жна паркува́тися — оштрафу́ють.

You can't park here — they'll fine you. (Prohibition — не мо́жна.)

Ти не му́сиш іти́ на ту зу́стріч, якщо́ не хо́чеш.

You don't have to go to that meeting if you don't want to. (Obligation lifted — не му́сиш.)

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Drill the opposites: не тре́ба = "don't bother, it's pointless"; не мо́жна = "don't you dare, it's forbidden"; не му́сиш = "you're free not to." Confusing не тре́ба with не мо́жна can turn "you needn't knock" into "you're forbidden to knock."

Source-language comparison

For an English speaker, two things are genuinely new. First, the grammar shifts under your feet depending on the word: with тре́ба and слід there is no subject — the person is dative (Мені́ тре́ба), so you must un-learn the reflex to start with "I." With пови́нен you do have a subject, but the word agrees with it like an adjective (я пови́нен / вона́ пови́нна), which English never asks of "should." Only му́сити behaves like a tidy English modal-with-a-subject. Second, the negation split — English leans on context to tell "mustn't" from "needn't," while Ukrainian lexicalises it: не мо́жна (forbidden) vs не тре́ба / не му́сиш (unnecessary). Build the habit of asking, before you negate, "forbidden or just unnecessary?"

For a Russian speaker, the frame is familiar but the words differ pointedly: Ukrainian тре́ба and слід where Russian uses на́до / ну́жно / сле́дует, му́сити (a живий, common verb in Ukrainian) where Russian leans on до́лжен / прихо́дится, and пови́нен / пови́нна / пови́нні rather than до́лжен / должна́. The agreement pattern transfers; just use the Ukrainian forms.

Common Mistakes

❌ Я тре́ба йти.

Wrong — тре́ба is impersonal; the person must be dative: Мені́ тре́ба йти.

✅ Мені́ тре́ба йти.

I need to go — dative experiencer + impersonal тре́ба.

❌ Вона́ пови́нен подзвони́ти.

Wrong — пови́нен must agree with the feminine subject: Вона́ пови́нна подзвони́ти.

✅ Вона́ пови́нна подзвони́ти.

She has to call — пови́нна agrees with вона́.

❌ Ми пови́нен запла́тити сього́дні.

Wrong — plural subject needs the plural form: Ми пови́нні запла́тити сього́дні.

✅ Ми пови́нні запла́тити сього́дні.

We have to pay today — пови́нні agrees with ми.

❌ Ти не тре́ба сюди́ заходи́ти — це забороне́но.

Wrong on two counts: тре́ба is impersonal (no 'ти'), and a prohibition needs не мо́жна, not не тре́ба: Сюди́ не мо́жна заходи́ти.

✅ Сюди́ не мо́жна заходи́ти.

You mustn't come in here — it's forbidden (не мо́жна).

❌ Я му́сю закінчи́ти сього́дні.

Wrong first-person form — it's му́шу (the с→ш alternation), not мусю: Я му́шу закінчи́ти сього́дні.

✅ Я му́шу закінчи́ти сього́дні.

I must finish today — му́шу is the correct я-form.

Key Takeaways

тре́ба — neutral "need to," impersonal + dative person + infinitive (Мені́ тре́ба йти); no present "to be."
му́сити — strongest compulsion, a conjugating verb (му́шу, му́сиш, му́сить, му́симо, му́сите, му́сять) with a nominative subject.
пови́нен — obligation, an agreeing adjective: пови́нен / пови́нна / пови́нне / пови́нні — match the subject's gender and number.
слід — bookish, advisory "one ought to," impersonal + infinitive.
Strength ladder: слід / тре́ба < пови́нен < му́сити.
Three negations, three meanings: не тре́ба (no need) ≠ не мо́жна (forbidden) ≠ не му́сиш / не пови́нен (not obliged).

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