a trebui (must / have to) | Romanian Grammar

A trebui is how Romanian says "must," "have to," and "need to." It has one defining peculiarity that sets it apart from every other verb you will learn: in its core obligation use it is impersonal and invariable — the form is trebuie for I, you, we, they, everyone. There is no eu trebuiesc, no noi trebuim. The subject of the obligation lives entirely inside the following să-clause. Once you accept that trebuie never changes, this verb becomes one of the easiest high-frequency words in the language — and its imperfect form, trebuia să, unlocks a nuance ("should have / was supposed to") that learners almost never produce.

The present: invariable trebuie + să

For obligation, trebuie takes a să-clause whose verb is conjugated for the real subject. Trebuie itself does not move.

Meaning	Romanian
I have to leave	Trebuie să plec
you have to leave	Trebuie să pleci
he/she has to leave	Trebuie să plece
we have to leave	Trebuie să plecăm
you (pl.) have to leave	Trebuie să plecați
they have to leave	Trebuie să plece

Notice the single column on the left: trebuie is identical in every row. All the person information is carried by the verb after să (plec, pleci, plece, plecăm...).

Trebuie să plec, am întârziat deja.

I have to go, I'm already late.

Trebuie să mergem la medic mâine.

We have to go to the doctor tomorrow.

Ei trebuie să vină până la prânz.

They have to come by noon.

💡

trebuie does not conjugate for the obligation sense. The person is shown by the verb inside the să-clause, never by trebuie. If you find yourself wanting to write trebuim or trebuiesc, stop — the form is trebuie and the agreement happens after să.

Past obligation: a trebuit să

For a completed obligation in the past — something you had to do and did — use the perfect compus a trebuit să. The auxiliary a / am / a is invariable here too, matching the impersonal nature of the verb.

A trebuit să plec mai devreme de la petrecere.

I had to leave the party early.

Au trebuit să anuleze concertul din cauza furtunii.

They had to cancel the concert because of the storm.

In careful standard Romanian you will see a trebuit as invariable even with plural subjects, though au trebuit (agreeing in number) is widespread and accepted in practice. Either way, the obligation was met: a trebuit să plec means I genuinely left.

The high-value form: imperfect trebuia să

This is the form learners rarely produce, and it is worth real attention. The imperfect trebuia să expresses an obligation that was standing, ongoing, or — crucially — unfulfilled. It is Romanian's main way to say "I was supposed to" and "I should have."

Trebuia să-l sun, dar am uitat complet.

I was supposed to call him, but I completely forgot.

Trebuia să știi asta de la început.

You should have known this from the start.

Trebuia să fim acolo la ora șapte, dar trenul a întârziat.

We were supposed to be there at seven, but the train was late.

The contrast with a trebuit să is sharp and meaningful:

Form	Meaning	Was it done?
A trebuit să plec.	I had to leave.	Yes — and I left.
Trebuia să plec.	I was supposed to leave / I should have left.	Implied no — I didn't (or it's left open).

💡

trebuia să + verb is your tool for regret and reproach: Trebuia să mă asculți ("You should have listened to me"), Trebuia să verific de două ori ("I should have double-checked"). English needs "should have"; Romanian gets there with one imperfect form. Learn this and your speech instantly sounds more native.

Probability: "must be" (logical deduction)

Just like English "must," trebuie să also expresses confident inference — not obligation but deduction. The clue is usually a stative verb (fie, aibă, fi) after să.

Trebuie să fie acasă, văd lumina aprinsă.

He must be home, I can see the light on.

Trebuie să fi plecat deja, mașina nu mai e aici.

They must have already left, the car's gone.

The form trebuie să fi + participle is the "must have done" of deduction — distinct from the obligation past a trebuit să.

Personal need: îmi trebuie + noun

When you need a thing (not an action), Romanian shifts to a different, dative construction: îmi trebuie + noun, literally "to me is needed." Here the verb does agree — with the thing needed, not with the person.

Îmi trebuie două ouă pentru rețetă.

I need two eggs for the recipe.

Cât timp îți trebuie ca să termini?

How much time do you need to finish?

Ne trebuie o mașină mai mare.

We need a bigger car.

So trebuie has two faces: the invariable modal with să + action (trebuie să plec), and the dative possessive with a clitic + noun (îmi trebuie ceva). They never collide because one is followed by să, the other by a noun.

Common Mistakes

❌ Eu trebuiesc să plec.

Incorrect — trebuie is invariable; there is no first-person form.

✅ Trebuie să plec.

I have to leave.

❌ Noi trebuim să mergem.

Incorrect — no plural conjugation of trebuie for obligation.

✅ Trebuie să mergem.

We have to go.

❌ A trebuit să-l sun, dar am uitat.

Incorrect for an unfulfilled plan — a trebuit implies the action happened.

✅ Trebuia să-l sun, dar am uitat.

I was supposed to call him, but I forgot.

❌ Îmi trebuie să o carte.

Incorrect — with a noun there is no să and no extra article.

✅ Îmi trebuie o carte.

I need a book.

Key Takeaways

For obligation, trebuie is invariable — the person is shown by the verb after să.
Past a trebuit să = an obligation that was fulfilled; imperfect trebuia să = "was supposed to / should have," usually unfulfilled.
trebuie să fie / să fi + participle also expresses logical deduction ("must be / must have").
To need a thing, switch to the dative îmi/îți/ne trebuie + noun.

Now practice Romanian

Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.

Start learning Romanian→