Musieć is the verb of must / have to — obligation, necessity, and strong inference ("that must be a mistake"). It is imperfective only and always takes a bare infinitive. Two things to nail: the spelling alternation s → sz in the muszę / muszą forms, and — far more important — the negation trap. In English "must not" forbids; in Polish nie musieć does the opposite — it removes obligation. Nie muszę iść means "I don't have to go," not "I must not go." This is arguably the single most dangerous false friend in Polish modality, and the bulk of this page is about getting it right.
Present tense — the s / sz alternation
| Person | Form | English |
|---|---|---|
| ja | muszę | I must / have to |
| ty | musisz | you must |
| on / ona / ono | musi | he / she / it must |
| my | musimy | we must |
| wy | musicie | you (pl.) must |
| oni / one | muszą | they must |
The stem mus- softens to musz- in exactly the two forms with the back-vowel nasal endings: muszę (1sg) and muszą (3pl). Everywhere else it stays plain s: musisz, musi, musimy, musicie. So the 1sg/3pl pair stands apart with sz — and they are told apart, as always, by the nasal vowel: muszę (-ę, "I"), muszą (-ą, "they").
Muszę już iść, bo spóźnię się na pociąg.
I have to go now, or I'll miss the train.
Musisz to zobaczyć na własne oczy.
You have to see it with your own eyes.
Wszyscy muszą mieć bilet przy wejściu.
Everyone has to have a ticket at the entrance.
Past tense
| Subject | Past form | English |
|---|---|---|
| ja (m. / f.) | musiałem / musiałam | I had to |
| ty (m. / f.) | musiałeś / musiałaś | you had to |
| on / ona / ono | musiał / musiała / musiało | he / she / it had to |
| my (vir. / non-vir.) | musieliśmy / musiałyśmy | we had to |
| wy (vir. / non-vir.) | musieliście / musiałyście | you (pl.) had to |
| oni / one | musieli / musiały | they had to |
Same vowel swap as chcieć: the virile plural is musieli (with -e-), against the singular musiał and non-virile musiały (with -a-).
Musiałam wziąć dzień wolny, bo dziecko zachorowało.
I had to take a day off because my child got sick. (woman speaking)
Musieliśmy długo czekać na autobus.
We had to wait a long time for the bus. (men/mixed → musieli-)
Future and conditional
The future is the imperfective compound: będę musiał / musiała ("I'll have to"), będziesz musiał / musiała, and so on:
Będę musiał zostać dłużej w pracy.
I'll have to stay longer at work. (man speaking)
The conditional musiałbym / musiałabym softens to "I'd have to / I would need to," common in hypotheticals:
Musiałbym to najpierw sprawdzić w kalendarzu.
I'd have to check it in my calendar first. (man speaking)
There is no imperative of musieć — you don't command someone to be obliged. To impose an obligation you switch to musisz as a statement, or to trzeba / a direct imperative.
Usage 1 — obligation and necessity
The core sense: something is required, by circumstances, rules, or your own will. Always musieć + infinitive:
Muszę oddać tę książkę do biblioteki do piątku.
I have to return this book to the library by Friday.
Nie wiem dlaczego, ale po prostu muszę to zrobić.
I don't know why, but I just have to do it.
A close relative is the impersonal trzeba ("one must / it's necessary"), used when there's no specific subject: Trzeba kupić chleb "We need to buy bread." See musieć vs trzeba vs powinien.
Usage 2 — strong inference ("must be")
Exactly like English, musieć also expresses confident deduction — "it must be the case":
To musi być jakaś pomyłka.
That must be some kind of mistake.
Musisz być wykończony po takiej podróży.
You must be exhausted after a trip like that.
Skoro nie odbiera, musi być na spotkaniu.
Since he's not picking up, he must be in a meeting.
The negation trap — nie musieć ≠ "must not"
Now the heart of the page. In English, negating "must" creates a prohibition: "you mustn't go." In Polish, negating musieć removes the obligation: nie musieć = "not have to," "don't need to." The two languages point in opposite directions.
Nie musisz dziś przychodzić, poradzimy sobie.
You don't have to come today, we'll manage. (NO obligation — not a prohibition)
Nie muszę tego tłumaczyć, prawda?
I don't have to explain this, do I?
So how do you actually say "you must not go" — a prohibition? Polish uses a different construction entirely. The two standard options:
- nie wolno (+ dative person) + infinitive — "it is not allowed / forbidden": Nie wolno ci tam wchodzić "You're not allowed in there."
- nie możesz / nie może… + infinitive — "you can't / may not": Nie możesz tego dotykać "You mustn't touch that."
Nie wolno tu palić.
No smoking here. (prohibition — NOT nie musieć)
Nie wolno ci nikomu o tym mówić.
You must not tell anyone about it. (lit. 'it is not allowed to you')
Nie możesz wychodzić, dopóki nie skończysz.
You can't leave until you finish.
Here is the whole obligation square in one view:
| English | Polish | Meaning |
|---|---|---|
| You must go. | Musisz iść. | obligation present |
| You don't have to go. | Nie musisz iść. | obligation absent (you may, but needn't) |
| You must not go. | Nie wolno ci iść. / Nie możesz iść. | prohibition |
| You may go. | Możesz iść. / Wolno ci iść. | permission |
For the może / wolno / można side of this square, see the modality page.
Common Mistakes
❌ Ja musę iść.
Incorrect — the 1sg softens to muszę (with sz), not 'musę'.
✅ Muszę iść.
I have to go.
❌ Nie musisz palić tutaj. — meaning to forbid smoking
Incorrect — this says 'you don't have to smoke here', not a prohibition.
✅ Nie wolno tu palić.
You must not smoke here.
❌ Musę zrobić zakupy. — wanting 'one needs to'
If there's no specific subject, the impersonal trzeba is more natural.
✅ Trzeba zrobić zakupy.
We need to do the shopping.
❌ Oni musiały czekać. — when 'they' includes men
Incorrect — a group with men takes the virile musieli, not musiały.
✅ Oni musieli czekać.
They had to wait.
❌ Musisz nie iść na to spotkanie.
Unnatural — to say 'you mustn't go', negate the modality, not the infinitive.
✅ Nie możesz iść na to spotkanie.
You mustn't go to that meeting.
Key Takeaways
- Present: muszę, musisz, musi, musimy, musicie, muszą — sz only in muszę / muszą.
- Past: musiał / musiała, virile plural musieli (with -e-) vs non-virile musiały; future będę musiał / musiała; no imperative.
- Two senses: obligation (muszę iść) and strong inference (to musi być pomyłka); always
- infinitive
- nie musieć = "not have to" (no obligation), never "must not."
- A prohibition is nie wolno (ci) + infinitive or nie możesz — not nie musisz.
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Start learning Polish→Related Topics
- Obligation: musieć, trzeba, miećA2 — How Polish expresses necessity and obligation — personal musieć, impersonal trzeba, the softer mieć + infinitive, and powinien — plus the negation trap where nie musieć means 'don't have to', not 'mustn't'.
- musieć vs trzeba vs powinien: Must, Should, Have ToB1 — How to express obligation in Polish — the personal must (musieć), the impersonal one-must (trzeba), the weaker should (powinien), and the negation trap where the negatives don't mirror the positives.
- Basic Negation with nieA1 — How to negate Polish verbs and other words with nie — placed directly before the negated word, with no auxiliary 'do', and how moving nie changes the meaning.
- móc — can, be ableA2 — Full reference for the irregular verb móc ('can, be able, may'): present mogę/możesz…/mogą, past mógł/mogła/mogli/mogły, conditional mógłbym — with the g/ż split, the ó↔o vowel drop, and móc vs umieć.
- chcieć — to wantA2 — Full reference for the irregular verb chcieć ('to want'): present chcę/chcesz…/chcą, past chciał/chciała/chcieli/chciały, conditional chciałbym — plus chcę + żeby for 'I want you to…' and the polite chciałbym for ordering.