English packs a whole scale of obligation into three flimsy words — must, should, ought to — and leaves you to guess the strength from context. Croatian makes the strength explicit by choosing a different verb: morati for hard obligation ("must, have to"), trebati for the softer "should" (and the unrelated "need"), and valjati for an impersonal, faintly proverbial "one ought to". This is a decision page: it gives compact present tables, but the weight is on which verb to reach for and — the part that genuinely changes meaning — how the negatives split apart, because ne moram, ne smijem and ne trebam are three different statements. For the full paradigms (l-participle, perfect, future, conditional), follow the links to morati and trebati.
The obligation scale in one line
| Verb | Strength | English gloss | Register / note |
|---|---|---|---|
| morati | strong, non-negotiable | must, have to | neutral, everyday |
| trebati | weaker, advisable | should, ought to (also: need) | neutral, everyday |
| valjati | general principle / norm | one ought to, it's good to | (formal) / proverbial |
The sorting rule: if the obligation is binding — a duty, a deadline, a law — use morati. If it's advice you could decline — "you should rest" — use trebati. If you're stating a general truth or norm with no particular subject ("one ought to keep one's word"), reach for the impersonal valjati.
Present tense, side by side
| Person | morati (must) | trebati (should/need) | valjati (ought, impers.) |
|---|---|---|---|
| ja | moram | trebam | — |
| ti | moraš | trebaš | — |
| on/ona/ono | mora | treba | valja |
| mi | moramo | trebamo | — |
| vi | morate | trebate | — |
| oni/one/ona | moraju | trebaju | — |
All three are regular a-class verbs in form. The difference is in how personal they are. Morati is fully personal (every person form is used). Valjati is impersonal — in this "ought" sense it only ever appears in the 3sg valja + infinitive, with no real subject. Trebati is the slippery one: it has a personal use ("need", with all persons) and an impersonal use ("should", typically 3sg treba + infinitive/da), which the next section unpacks.
morati — strong obligation
Moram do ponoći predati prijavu, inače propada rok.
I have to submit the application by midnight, otherwise the deadline lapses. — binding obligation.
Moraš to vidjeti vlastitim očima, ne mogu ti opisati.
You have to see it with your own eyes, I can't describe it to you. — emphatic 'must'.
trebati — weaker "should", and the personal "need"
Trebati leads a double life. Personal "need" takes an accusative object — Trebam odmor ("I need a rest"), with you as the subject. Impersonal "should/ought" uses treba + infinitive or da — Treba učiti ("One should study / studying is needed"). And the everyday personal "should" — Trebaš učiti ("You should study") — agrees with the subject. The contrast Trebaš učiti vs Treba učiti is exactly personal-advice vs general-norm.
Trebao bi se više odmarati, izgledaš iscrpljeno.
You should rest more, you look exhausted. — soft advice; note the conditional 'trebao bi' softens it further.
Treba dvaput provjeriti prije nego što pošalješ.
One should double-check before sending. — impersonal 'treba' + infinitive.
Trebam tvoju pomoć s ovim.
I need your help with this. — personal 'need' + accusative 'pomoć'.
valjati — the impersonal "one ought"
Valjati in the obligation sense is impersonal and somewhat formal or proverbial: Valja održati riječ ("One ought to keep one's word"). It states a norm, not a personal duty, and is at home in maxims and elevated prose. (Its other, everyday meaning is "to be worth / be any good" — Ne valja ti taj plan, "That plan of yours is no good" — but that's a separate sense.)
Valja dvaput mjeriti, a jednom rezati.
One ought to measure twice and cut once. — proverbial 'valja' + infinitive.
Valja imati na umu da pravila vrijede za sve.
One ought to bear in mind that the rules apply to everyone. — (formal) impersonal.
The negatives — where it really matters
This is the heart of the matter, and the place English transfers go wrong. English "mustn't" and "don't have to" look like a pair but mean opposites, and Croatian forces you to get it right by using different verbs.
| Negative | Means | Because… |
|---|---|---|
| ne moram | I don't have to (no obligation) | the duty simply isn't there |
| ne smijem | I mustn't (it's forbidden) | a rule forbids it — a different verb, smjeti |
| ne trebam | I don't need to (it's unnecessary) | the action isn't called for |
The crucial trap: English "you mustn't" is a prohibition, and Croatian expresses prohibition with ne smjeti, not with negated morati. Ne moraš means the opposite — "you're under no obligation". So ne smiješ (forbidden) and ne moraš (free not to) are near-opposites despite the English overlap. The verb of permission, smjeti, lives on the can-verbs page; the obligation/permission interplay is detailed at the obligation cluster.
Ne moraš doći ako ti se ne da, nije obavezno.
You don't have to come if you don't feel like it, it's not compulsory. — absence of obligation: 'ne moraš'.
Ne smiješ ovdje parkirati, odvest će ti auto.
You mustn't park here, they'll tow your car. — prohibition: 'ne smiješ', NOT 'ne moraš'.
Ne trebaš mi ništa donositi, dođi samo ti.
You don't need to bring me anything, just come yourself. — unnecessary: 'ne trebaš'.
How to choose, in practice
- Is it a binding duty, deadline, or law (you have no real choice)? → morati (moram / moraš).
- Is it advice the person could decline ("you should…")? → trebati, often softened with the conditional trebao bi (trebaš / trebao bi).
- Is it a general norm or maxim with no real subject ("one ought to…")? → valjati (valja
- infinitive), formal/proverbial.
- For the negative, decide what you mean first: no obligation → ne moram; forbidden → ne smijem; unnecessary → ne trebam.
Ne moraš ostati do kraja, ali ne smiješ otići bez pozdrava.
You don't have to stay till the end, but you mustn't leave without saying goodbye. — 'ne moraš' (no obligation) vs 'ne smiješ' (forbidden), in one sentence.
Common Mistakes
❌ Ne moraš pušiti ovdje. (meaning: it's forbidden)
Meaning slip — 'ne moraš' = 'you don't have to'; for a prohibition use 'ne smiješ pušiti'.
✅ Ne smiješ pušiti ovdje.
You mustn't smoke here.
❌ Trebam učiti za ispit. (meaning: studying is needed in general)
If you mean the general 'one should study', use impersonal 'treba učiti'. 'Trebam učiti' is the personal 'I need/ought to study' — fine if that's what you mean, but not the impersonal norm.
✅ Treba učiti za ispit.
One should study for the exam. — impersonal norm.
❌ Valjam održati riječ.
Form error — in the 'ought' sense 'valjati' is impersonal: only 'valja' + infinitive, never a 1sg '*valjam'.
✅ Valja održati riječ.
One ought to keep one's word.
❌ Moram tvoju pomoć.
Wrong verb — 'must' (morati) takes an action, not an object. To 'need' a thing, use 'trebati' + accusative: 'Trebam tvoju pomoć'.
✅ Trebam tvoju pomoć.
I need your help.
❌ Ne smiješ raditi danas, slobodan si.
Meaning slip — 'you're off today' means no obligation ('ne moraš raditi'), not a prohibition. 'Ne smiješ raditi' would mean working is forbidden.
✅ Ne moraš raditi danas, slobodan si.
You don't have to work today, you're off.
Key Takeaways
- morati = strong obligation (must/have to); trebati = weaker "should" (and personal "need" + accusative); valjati = impersonal "one ought" (valja
- infinitive, formal/proverbial).
- Trebaš učiti (personal "you should") vs Treba učiti (impersonal "one should") — same verb, different person and reach.
- The negatives are NOT interchangeable: ne moram (don't have to) vs ne smijem (mustn't, forbidden — a different verb, smjeti) vs ne trebam (don't need).
- English "mustn't" ≠ negated morati: prohibition is ne smjeti; ne morati is the absence of obligation.
- Valjati "ought" is impersonal only — never a personal *valjam. Full paradigms live on the dedicated pages.
Now practice Croatian
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Croatian→Related Topics
- morati (must/have to)A2 — Obligation modal 'must'.
- trebati (to need / should)B1 — The two-faced trebati: personal 'need' and impersonal 'should'.
- smjeti / moći / znati (can: permission/ability/skill)B1 — The three Croatian verbs English collapses into 'can' — moći (ability/possibility), smjeti (permission), znati (acquired skill) — with the decision logic and the three negatives that actually differ in meaning.
- Obligation: morati, trebati, valjaA2 — Expressing 'must', 'should', and 'need to'.
- da + present vs the InfinitiveB1 — When to use the infinitive and when to use a da + present clause after modal and volition verbs — the same-subject choice, the different-subject rule, and the register split.
- Accusative: The Direct ObjectA1 — The accusative as the default object of transitive verbs.