Verb Reference: Треба / Потрібно / Можна (necessity) | Ukrainian Grammar

Type: impersonal predicatives (предикати́вні прислі́вники / категорі́я ста́ну) — single invariable words, not conjugating verbs Core members: тре́ба, потрі́бно, мо́жна, не мо́жна, слід, ва́рто Frame: dative experiencer + infinitive — Мені́ тре́ба йти "I have to go"

This is the most important page in the whole "modality" corner for a beginner, because it teaches the single most common way Ukrainian says need, may, and must not — and that way is not a verb you conjugate. Words like тре́ба ("[it is] necessary"), мо́жна ("[it is] permitted"), потрі́бно ("[it is] needed") are impersonal predicatives: frozen, invariable forms that never change for person, gender or number. You don't say "I need" by inflecting тре́ба for "I" — there is no first-person form. Instead you put the person in the dative and the action in the infinitive: Мені́ тре́ба... literally "to-me [it-is] necessary...". Because there is no nominative subject, English speakers must unlearn the urge to start the sentence with "I."

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These words do not conjugate — there is no я тре́баю or ти мо́жеш-style paradigm. The only thing that changes is the tense, and that is carried by the verb бу́ти tacked on: тре́ба було́ (past), тре́ба бу́де (future). Everything else stays a fixed block: dative + предикатив + infinitive.

The core frame: dative + predicative + infinitive

Memorise the slot order: (experiencer in the dative) + (predicative) + (infinitive). The dative names who has the need or permission; the predicative names the modal flavour; the infinitive names the action. The dative slot is optional — drop it and you get a general, "one"-style statement (Тут не мо́жна кури́ти "One mustn't smoke here").

Predicative	Meaning	Frame
тре́ба	need to, have to, must (necessity)	dative + infinitive
потрі́бно	need to, it is necessary (a touch more formal than тре́ба)	dative + infinitive
мо́жна	may, one can, it is allowed	(+ dative) + infinitive
не мо́жна	must not, may not (prohibition)	(+ dative) + infinitive
слід	should, ought to (advice; mildly formal)	dative + infinitive
ва́рто	it is worth (-while), should	(+ dative) + infinitive
необхі́дно	it is essential / indispensable (formal)	dative + infinitive

Note the stress: all are root-stressed except the single-syllable слід (unmarked, монослог). тре́ба and мо́жна are the everyday, neutral choices; потрі́бно and необхі́дно lean (formal); слід is (formal) advice; ва́рто is fully neutral.

Мені́ тре́ба ще сього́дні зайти́ в апте́ку — у нас закінчи́лися лі́ки.

I need to drop by the pharmacy today — we've run out of medicine. (dative Мені́ + тре́ба + infinitive зайти́; no nominative 'I'.)

Вам потрі́бно запо́внити цю фо́рму до кінця́ ти́жня.

You need to fill out this form by the end of the week. (потрі́бно with the dative Вам; slightly more official than тре́ба.)

Тут мо́жна фотографува́ти? — Так, але без спа́лаху.

Can one take photos here? 'Yes, but without flash.' (мо́жна with no dative = a general 'is it allowed'.)

"May" vs "must not": мо́жна and не мо́жна

Мо́жна asks for or grants permission ("may I / one may"); its negation не мо́жна is a flat prohibition ("you mustn't / it's forbidden"). Pay attention here: не мо́жна is not merely "one cannot" in the ability sense — for "I'm unable to," Ukrainian uses the conjugating verb не мо́жу (from могти́). Не мо́жна is about rules and permission, not physical ability.

Мо́жна мені́ сі́сти бі́ля вікна́?

May I sit by the window? (мо́жна + dative мені́ + infinitive — the polite 'may I'.)

На черво́не сві́тло перехо́дити не мо́жна.

You must not cross on a red light. (не мо́жна = prohibition, a rule — not 'unable'.)

Ді́тям не мо́жна так пі́зно лягати спа́ти.

Children shouldn't go to bed that late. (dative Ді́тям + не мо́жна — the rule applies to them.)

слід and ва́рто: "should" and "worth it"

For softer advice — "you ought to," "it would be a good idea to" — Ukrainian reaches for слід (a touch formal, common in written advice and instructions) and ва́рто ("it's worth it"). Both keep the same dative-plus-infinitive frame. Слід is the modal closest to English "should"; ва́рто adds the nuance "the action is worthwhile."

Тобі́ слід відпочи́ти — ти ма́єш вто́млений ви́гляд.

You should get some rest — you look tired. (слід + dative Тобі́ + infinitive; gentle advice.)

Ва́рто заброньова́ти столи́к зазда́легідь, там за́вжди бага́то люде́й.

It's worth booking a table in advance; it's always crowded there. (ва́рто = 'it's worthwhile'; no dative needed here.)

Tense: there is no conjugation — бу́ти carries it

This is the heart of the page. Since the predicatives are frozen, you cannot push them into the past or future by changing their endings. Instead you add the neuter past or future of бу́ти as a separate word: тре́ба було́ "it was necessary," тре́ба бу́де "it will be necessary." The бу́ти form is always neuter / 3rd person (було́ / бу́де), because the whole construction is impersonal — there is no subject for it to agree with.

Tense	Form	Example
Present	тре́ба / потрі́бно / мо́жна (bare)	Мені́ тре́ба йти.
Past	було́	Мені́ тре́ба було́ йти.
Future	бу́де	Мені́ тре́ба бу́де йти.
Conditional	було́ б	Тобі́ тре́ба було́ б відпочи́ти.

Word order is flexible — тре́ба було́ and було́ тре́ба both occur — but тре́ба було́ is the more usual order. The same trick works for мо́жна (мо́жна було́ "it was allowed," мо́жна бу́де "it will be allowed"), слід (слід було́), and ва́рто (ва́рто було́ "it would have been worth it / one should have").

Мені́ тре́ба було́ ще вчо́ра попере́дити їх, а я забу́в.

I should have warned them yesterday, but I forgot. (past: тре́ба + було́, the бу́ти form stays neuter.)

За́втра нам тре́ба бу́де ра́но встава́ти — потяг о шо́стій.

Tomorrow we'll have to get up early — the train is at six. (future: тре́ба + бу́де + dative нам.)

Ра́ніше тут мо́жна було́ паркува́ти безкошто́вно.

It used to be possible to park here for free. (мо́жна було́ — past permission via бу́ти.)

When a NOUN is needed: потрі́бен / потрі́бна (the agreeing exception)

Here is the one place the system breaks the "invariable" rule, and it catches everyone. When what you need is a thing (a noun) rather than an action (an infinitive), Ukrainian switches from the frozen потрі́бно to the adjective-style потрі́бен, which agrees with that noun in gender and number — and the thing needed lands in the nominative, not the accusative. Literally it's "to-me is-needed a-dictionary," with "dictionary" as the grammatical subject.

Gender / number of the thing needed	Form of потрібен	Example
masculine	потрі́бен	Мені́ потрі́бен сло́вник.
feminine	потрі́бна	Мені́ потрі́бна допомо́га.
neuter	потрі́бне	Мені́ потрі́бне рі́шення.
plural	потрі́бні	Мені́ потрі́бні окуля́ри.

So the rule is clean: need to do something → потрі́бно/тре́ба + infinitive (frozen); need a thing → потрі́бен + nominative noun (agreeing). With тре́ба, by contrast, the thing needed slips into the genitive (Мені́ тре́ба сло́вника), which is the older, more colloquial pattern.

Мені́ потрі́бен твій но́мер телефо́ну — як з тобо́ю зв’яза́тися?

I need your phone number — how do I reach you? (потрі́бен agrees with masculine но́мер; the thing is nominative.)

Нам потрі́бні нові́ ме́блі, ці вже зо́всім старі́.

We need new furniture; this stuff is really old. (plural потрі́бні agreeing with ме́блі.)

Тобі́ ще тре́ба ма́сла? — Так, купи́, будь ла́ска.

Do you still need butter? 'Yes, buy some, please.' (with тре́ба the noun goes GENITIVE: ма́сла.)

How the predicatives differ from му́сити and пови́нен

Ukrainian also has two conjugating / agreeing ways to say "must," and it's worth knowing the contrast so you pick the right register. Му́сити is a real verb — it conjugates (я му́шу, ти му́сиш...) and expresses strong obligation or compulsion ("I am forced to"). Пови́нен is a short adjective — it agrees with its subject in gender and number (він пови́нен, вона́ пови́нна, вони́ пови́нні) and means "ought to / is supposed to." Both take a nominative subject, unlike the dative-frame predicatives. The full contrast lives on тре́ба / му́сити / пови́нен.

Construction	Type	Subject case	Flavour
тре́ба + inf.	invariable predicative	dative	plain necessity, neutral
му́сити + inf.	conjugating verb	nominative	strong compulsion, "forced to"
пови́нен + inf.	agreeing short adjective	nominative	obligation, "supposed to"

Мені́ тре́ба йти, але я не му́шу — про́сто хо́чу.

I need to go, but I'm not forced to — I just want to. (тре́ба = plain need; не му́шу = not compelled — note the nominative 'я' with the verb.)

Source-language comparison

For an English speaker, the leap is structural. English "I must / I have to / I need to" all start with a subject ("I") and a verb. Ukrainian тре́ба does neither: it has no subject and no verb to conjugate, and the "I" becomes the dative мені́ — the person is the recipient of a necessity that exists impersonally, "out there." This is the same dative-experiencer logic behind Мені́ хо́лодно ("I'm cold," lit. "to-me [it-is] cold") and Мені́ подо́бається ("I like it," lit. "to-me it-is-pleasing"). Once you see тре́ба as one more member of that impersonal-dative family, it stops feeling alien.

For a Russian speaker: standard Ukrainian is тре́ба, not на́до; *мо́жна, not *мо́жно; and "we have to" is нам тре́ба. Keep the apostrophe in зв’яза́тися and say в Украї́ні, not "на".

Common Mistakes

❌ Я тре́ба йти.

Wrong case — the experiencer is the DATIVE, never the nominative: Мені́ тре́ба йти. There is no nominative subject with тре́ба.

✅ Мені́ тре́ба йти.

I need to go.

❌ Мені́ тре́баю купи́ти хліб.

тре́ба does NOT conjugate — there is no *тре́баю. It is a frozen predicative: Мені́ тре́ба купи́ти хліб.

✅ Мені́ тре́ба купи́ти хліб.

I need to buy bread.

❌ Мені́ тре́бало піти́ ра́ніше.

To put it in the past you don't inflect тре́ба — you add neuter було́: Мені́ тре́ба було́ піти́ ра́ніше.

✅ Мені́ тре́ба було́ піти́ ра́ніше.

I should have left earlier.

❌ Мені́ потрі́бно нови́й телефо́н.

For a NOUN you need the agreeing потрі́бен + nominative: Мені́ потрі́бен нови́й телефо́н. потрі́бно is for an infinitive, not a thing.

✅ Мені́ потрі́бен нови́й телефо́н.

I need a new phone.

❌ Я не мо́жна кури́ти тут.

не мо́жна is impersonal — no nominative subject. Either Тут не мо́жна кури́ти ('one mustn't smoke here') or, for inability, Я не мо́жу кури́ти.

✅ Тут не мо́жна кури́ти.

You must not smoke here.

Key Takeaways

тре́ба, потрі́бно, мо́жна, не мо́жна, слід, ва́рто are invariable impersonal predicatives — they never conjugate.
The frame is dative experiencer + predicative + infinitive: Мені́ тре́ба йти. No nominative subject.
Tense comes from бу́ти, always neuter: тре́ба було́ (past), тре́ба бу́де (future), тре́ба було́ б (conditional).
мо́жна = permission ("may"); не мо́жна = prohibition ("must not"), not inability (that's не мо́жу).
For a noun, switch to the agreeing потрі́бен / потрі́бна / потрі́бне / потрі́бні
- nominative (Мені́ потрі́бен сло́вник); with тре́ба the noun goes genitive (тре́ба ма́сла).
Contrast with the conjugating му́сити and the agreeing пови́нен, which both take a nominative subject.

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