smět — May, Be Allowed

Czech has a dedicated verb for permission: smět, "to be allowed to, may." It is a modal verb, so it takes a bare infinitive after it — Smím vstoupit? ("May I come in?"). On its own, smět is fairly low-frequency in the affirmative; in everyday speech people often reach for moci ("can") instead. But its negative, nesmět, is one of the most important verbs in the language, because it is how Czech says "must not" — and that is exactly where English speakers go wrong. The single most damaging mistake on this page is using nemuset ("don't have to") when you mean nesmět ("must not"). Get this one distinction right and you will avoid producing sentences that mean the opposite of what you intend.

The present tense of smět

smět conjugates like rozumět and umět: a long í runs through the singular and the -ě- surfaces in the third-person plural smějí. The one form to watch is smějí (and its negative nesmějí) — note the ě, not a bare í.

smět + infinitive

Like every Czech modal, smět governs a bare infinitive — no preposition, no to-equivalent. The conjugated smět carries the person and tense; the infinitive supplies the action.

For how the infinitive's aspect is chosen after a modal, see Aspect after Modal Verbs.

The polite Smím prosit?

A fixed, charming use of smět survives in formal etiquette: Smím prosit? — literally "May I beg?", but functionally "May I have this dance?". You will hear it at a ball or a wedding when someone invites a partner onto the floor. It is unmistakably (formal) and slightly old-fashioned, which is exactly its appeal.

nesmět — "must not", the prohibition verb

Here is the heart of the page. The negative nesmět does not mean "may not" in the weak English sense of "perhaps not." It means "must not / is forbidden to / is not allowed to" — a hard prohibition. It is the exact mirror image of muset ("must"): muset imposes an obligation to do something; nesmět imposes an obligation not to do it.

The double negative in Nesmíš to říct nikomu is obligatory in Czech: the verb is negated and the pronoun is negated (nikomu, "to nobody"). This concord of negatives is normal Czech grammar, not a mistake.

The trap: nesmět vs nemuset

English collapses two very different ideas into one shape, "don't have to" / "mustn't," and learners carry that confusion into Czech. Czech keeps them strictly apart:

• nemuset = "don't have to" — the obligation is removed; the action is optional.
• nesmět = "must not" — the action is forbidden.

These two sentences look almost identical but are worlds apart: the first releases you from a duty, the second forbids you from acting. For a fuller treatment of this contrast, see muset vs nesmět: 'Must' and 'Must Not'.

smět vs moci for permission

Both smět and moci can ask for or grant permission, but they pull in different directions:

• smět is purely about permission — whether something is allowed by a rule, an authority, or politeness.
• moci ("can, be able to") is primarily about ability and possibility, but in everyday speech it doubles as a softer, more casual way to ask permission.

So Smím otevřít okno? foregrounds the rule ("Am I permitted to open the window?"), while the more colloquial Můžu otevřít okno? ("Can I open the window?") is what most people actually say at the dinner table. In strict or institutional contexts — signs, regulations, formal requests — smět is the precise choice.

For the full range of moci, see moci / moct — Can, May, Be Able.

Past and conditional

The past tense uses the l-participle směl / směla / smělo (plural směli / směly / směla) with the auxiliary, exactly like any other verb. The conditional adds by / bych.

Here the neuter-plural and feminine-plural participle nesměly agrees with a group spoken of as děti taken as feminine/mixed; with an all-masculine-animate group it would be nesměli, and a purely neuter plural subject would take -a (ta zvířata sem nesměla — "those animals were not allowed in here"). See Plural Agreement: -li, -ly, -la.

Common Mistakes

The classic error: reaching for nemusíš to translate "you mustn't." Nemusíš kouřit literally tells someone they are free not to smoke — the opposite of a no-smoking rule.

Czech modals take a bare infinitive. Do not add a preposition to mimic the English to.

Each person needs its own ending: my takes smíme, never smí.

Smím prosit? is a complete, fixed formula; tacking on another prosím is redundant.

Key Takeaways

• smět = "may, be allowed to"; present smím, smíš, smí, smíme, smíte, smějí, always with a bare infinitive.
• nesmět = "must not / is forbidden to" — a true prohibition, the mirror of muset.
• Never use nemuset ("don't have to") to express a prohibition; that releases the obligation instead of imposing one.
• For casual permission, Czechs often prefer moci (Můžu…?); smět is the precise, rule-focused option.
• Remember the polite fixed phrase Smím prosit? at a dance.