muset — Must, Have To | Czech Grammar

muset is the Czech verb for obligation — "must", "have to", "have got to". It is grammatically simple: it is followed straight by an infinitive, with no preposition in between. The hard part is not the form but one piece of meaning: the negative nemuset does not mean "must not". It means "don't have to". Getting this wrong is one of the most common and most consequential errors English speakers make, because it flips a permission into the absence of an obligation. This page is about using muset correctly and steering clear of that trap. (For the full paradigm across every tense, see the reference card.)

The present, in brief

You only need a quick look at the present here:

Person	Affirmative	Negative
já	musím	nemusím
ty	musíš	nemusíš
on/ona/ono	musí	nemusí
my	musíme	nemusíme
vy	musíte	nemusíte
oni/ony	musí (musejí)	nemusí (nemusejí)

It is an ordinary -í- class verb. What matters from here on is what these forms mean and what comes after them.

muset + infinitive

muset is a modal verb, so it takes a bare infinitive as its complement — exactly like English "must", but unlike "have to", there is no linking word.

Musím už jít, mám sraz v sedm.

I have to go now, I've got a meeting at seven.

Musíš pracovat o víkendu, nebo můžeš zůstat doma?

Do you have to work this weekend, or can you stay home?

The obligation can come from outside (a rule, a boss, circumstances) — this is the everyday "have to". In the past you simply use the past of muset: Musel jsem dlouho čekat "I had to wait a long time".

The aspect of the infinitive after muset

muset does not choose your aspect for you — the infinitive does, exactly as it would in a normal clause. Use the perfective when the obligation is to complete one specific thing, and the imperfective when it is to carry out an activity, a habit, or an open-ended process.

Musím to dodělat dnes, zítra to odevzdávám.

I have to finish it today, I'm handing it in tomorrow.

Musím každý den cvičit, jinak mě bolí záda.

I have to exercise every day, otherwise my back hurts.

In the first sentence dodělat (perfective) frames the homework as one job to be completed; in the second cvičit (imperfective) frames the exercise as a recurring activity. The same logic you already use for choosing aspect applies unchanged here.

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Think of muset as transparent to aspect: it stacks the meaning "obligation" on top of whatever the infinitive already says about completion. Pick the infinitive's aspect first, then add muset.

The crucial split: nemuset vs nesmět

Here is the heart of the page. English "must" has an asymmetric negative: "you must not" is a prohibition, not the negation of an obligation. Czech is more logical and splits the two meanings between two different verbs:

Czech	Literal logic	English
Musím jít.	obligation present	I must / have to go.
Nemusím jít.	obligation absent	I don't have to go (but I may).
Nesmím jít.	permission absent	I must not / am not allowed to go.

So nemuset is "free of obligation" and nesmět is "denied permission". They are not interchangeable, and confusing them can reverse your meaning in a way that matters — telling a child nemusíš tam chodit ("you don't have to go there") when you meant nesmíš tam chodit ("you're not allowed to go there") gives exactly the wrong instruction.

Nemusíš na mě čekat, přijdu klidně sám.

You don't have to wait for me, I'll happily come on my own.

Tady nesmíš kouřit, je to nemocnice.

You're not allowed to smoke here, it's a hospital.

Nemusíme spěchat, máme spoustu času.

We don't have to rush, we've got plenty of time.

Děti dnes nesmějí ven, venku je bouřka.

The kids aren't allowed out today, there's a storm outside.

nesmět is smět "to be allowed" with the negative prefix; it is treated fully on its own page. For now, lock in the pairing: prohibition = nesmět, not nemuset.

A bonus meaning: muset of probability

Like English "must", muset also expresses a confident inference — "it must be the case that…". This is the epistemic use, and it too takes an infinitive (very often the infinitive of být).

To musí být nějaký omyl, takovou částku jsem neobjednal.

That must be some mistake, I didn't order such an amount.

Musíš být po té cestě hrozně unavený.

You must be terribly tired after that trip.

Common Mistakes

❌ Nemusíš tam chodit!

Wrong if you mean a prohibition ('you must not go there') — nemusíš only says 'you don't have to'; to forbid, use nesmíš.

✅ Nesmíš tam chodit!

You must not go there!

❌ Nemusím jít.

Wrong if you mean 'I'm not allowed to go' — this actually says 'I don't have to go'; for 'not allowed' use nesmím.

✅ Nesmím jít.

I'm not allowed to go.

❌ Musím k tomu pracovat o víkendu.

Incorrect — muset takes a bare infinitive, with no preposition like the English 'have to'.

✅ Musím pracovat o víkendu.

I have to work this weekend.

❌ Musím jdu domů hned teď.

Incorrect — muset is followed by the infinitive jít, not a conjugated verb.

✅ Musím jít domů hned teď.

I have to go home right now.

❌ Musím to dělat do pěti hodin, pak končím.

Incorrect when you mean to complete it — a one-off deadline calls for the perfective udělat, not the imperfective dělat.

✅ Musím to udělat do pěti hodin, pak končím.

I have to get it done by five, then I'm finishing.

Key Takeaways

muset = "must / have to"; it takes a bare infinitive, no preposition.
The infinitive keeps its own aspect — perfective for a completed task, imperfective for an activity or habit.
nemuset = "don't have to" (no obligation), never "must not".
For a prohibition, use nesmět (nesmíš tam chodit), not nemuset.
muset can also mean a confident inference: To musí být omyl "That must be a mistake".

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