muset — must, to have to | Czech Grammar

Muset is the everyday Czech word for "must" and "to have to." It is a modal verb: it does not describe an action on its own but combines with a second verb in the infinitive — Musím jít ("I have to go"). The single most important thing on this page is what happens under negation, because it is exactly the opposite of what English learners expect. Get that one point right and you have mastered the verb.

Conjugation class

Muset belongs to the Class IV (-í-) pattern of prosit / trpět verbs: the present-tense endings are -ím, -íš, -í, -íme, -íte, -í. You will also meet the spelling musit in older or more bookish texts; it is the same verb, fully interchangeable, but muset is the standard modern form and the one you should write.

Person	Present
já	musím
ty	musíš
on / ona / ono	musí
my	musíme
vy	musíte
oni / ony / ona	musí / musejí

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The third-person plural has two living forms: the shorter musí and the fuller musejí (sometimes spelled musí / musejí). Both are standard and you will hear both; musí is more common in speech, musejí is a touch more careful. Pick either — just be consistent within a sentence.

Musím pracovat do pěti.

I have to work until five.

Musíš si odpočinout, vypadáš unaveně.

You have to get some rest, you look tired.

Děti musí být doma do osmi.

The kids have to be home by eight.

The key point: nemuset is NOT "must not"

This is where almost every English speaker slips. In English, the negation of "must" looks like it should mean the opposite of the obligation, but English actually splits the meaning across two phrases:

"you don't have to" = there is no obligation (it's optional)
"you must not" = there is a prohibition (it's forbidden)

Czech keeps these completely separate, using two different verbs:

nemuset = don't have to / needn't (no obligation) — the plain negation of muset
nesmět = mustn't / not be allowed to (prohibition) — the negation of smět, "to be allowed"

So nemusíš jít does not mean "you mustn't go." It means "you don't have to go" — going is entirely up to you. If you want to forbid someone from going, you need nesmíš jít.

Nemusíš jít, jestli nechceš.

You don't have to go if you don't want to.

Nesmíš jít, je to zakázané.

You mustn't go, it's forbidden.

Zítra nemusím vstávat brzy, je sobota.

Tomorrow I don't have to get up early, it's Saturday.

Tady nesmíte kouřit.

You're not allowed to smoke here.

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A reliable test: if you could replace the English with "don't have to / needn't," use nemuset. If you could replace it with "is forbidden / not allowed," use nesmět. Confusing them produces real misunderstandings — telling a guest Nemusíte si sundat boty means "you needn't take your shoes off," not "you mustn't."

Past tense

The past uses the l-participle of muset plus the present-tense auxiliary být (jsem, jsi, …), which is dropped in the third person. The participle agrees in gender and number with the subject.

Subject	Past form
já (m.) / (f.)	musel jsem / musela jsem
ty (m.) / (f.)	musel jsi / musela jsi
on / ona / ono	musel / musela / muselo
my (m.) / (f.)	museli jsme / musely jsme
vy (m.) / (f.)	museli jste / musely jste
oni / ony / ona	museli / musely / musela

Včera jsem musel zůstat v práci dlouho.

Yesterday I had to stay at work late. (male speaker)

Museli jsme přestoupit v Brně.

We had to change trains in Brno.

Nemusela jsem nic platit, bylo to zdarma.

I didn't have to pay anything, it was free. (female speaker)

Future tense

Because muset is imperfective, its future is formed analytically with the future of být (budu, budeš, …) plus the infinitive muset.

Person	Future
já	budu muset
ty	budeš muset
on / ona / ono	bude muset
my	budeme muset
vy	budete muset
oni / ony / ona	budou muset

Budeme muset počkat na příští vlak.

We'll have to wait for the next train.

Bude muset začít znovu od začátku.

He'll have to start again from the beginning.

Conditional

The conditional (musel bych, "I would have to") softens the obligation or makes it hypothetical. It combines the l-participle with the conditional auxiliary bych, bys, by, ….

Musel bych se nejdřív zeptat šéfa.

I'd have to ask the boss first. (male speaker)

To bys musela vědět ty, ne já.

That's something you'd have to know, not me. (female addressee)

What follows muset

Muset always takes a dependent infinitive — the second verb is never finite. The aspect of that infinitive carries its own meaning: a perfective infinitive points to a single completed action, an imperfective one to a process or a general state of affairs.

Musím napsat ten e-mail ještě dnes.

I have to write that email today. (perfective: get it done)

Musím psát každý den, jinak se to nenaučím.

I have to write every day, otherwise I won't learn it. (imperfective: ongoing habit)

Common mistakes

❌ Nemusíš kouřit tady — chtěl jsem říct, že je to zakázané.

Wrong if you mean a prohibition: nemusíš = 'you needn't', not 'you mustn't'.

✅ Nesmíš tady kouřit.

Correct: nesmět expresses a prohibition.

❌ Musím že jdu.

Wrong: muset never takes a 'že' clause.

✅ Musím jít.

Correct: muset takes a bare infinitive.

❌ Já musím pracoval včera.

Wrong: mixing present musím with a past participle.

✅ Včera jsem musel pracovat.

Correct: the past is musel + auxiliary, and the second verb stays infinitive.

❌ Ona musíš odejít.

Wrong: musíš is the 'ty' form; the verb must agree with 'ona'.

✅ Ona musí odejít.

Correct: third person singular is musí.

Key takeaways

muset = "have to / must"; it always takes an infinitive.
The 3rd-person plural is musí or musejí — both standard.
nemuset = "don't have to" (no obligation), never "mustn't."
To say "mustn't / not allowed," use nesmět: see muset vs nesmět.

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