moci / moct — can, to be able to | Czech Grammar

Moci ("can, to be able to") is the Czech verb for general possibility and ability — "Can I come in?", "I can't make it today." It is the modal that pairs with a bare infinitive, and it is notorious for two things: a stem that flips between h and ž depending on the form, and a sharp split between the literary infinitive moci and the everyday spoken one moct. Get the alternation straight and the rest falls into place. This page lays out the full paradigm in both registers and shows where moci stops and its rivals umět and smět begin.

Two infinitives, one verb

The infinitive itself has two forms:

moci — the literary/written form (formal).
moct — the colloquial spoken form (informal), now overwhelmingly the more common one in speech.

They are the same verb; pick the register. You will read nemohu přijít in an email and hear nemůžu přijít on the phone.

The present tense

Here is the famous alternation. The verb has an older h-stem (mohu, mohou) that survives in literary Czech, and a newer ž-stem (můžu, můžou) that dominates everyday speech. The middle forms (můžeš, může, můžeme, můžete) are the same in both registers.

Person	Literary (formal)	Spoken (informal)	Meaning
já	mohu	můžu	I can
ty	můžeš	můžeš	you can (sg.)
on / ona / ono	může	může	he / she / it can
my	můžeme	můžeme	we can
vy	můžete	můžete	you can (pl./formal)
oni	mohou	můžou	they can

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The alternation isn't random — it's a sound change called palatalization, the same one that turns kniha (book) into knize. The original consonant is h (you still see it in mohu, mohou and in the past mohl); before the front vowel e it softened to ž (můžeš, může). Modern spoken Czech then extended the ž back into the já and oni forms, giving můžu, můžou. So: h survives in the bookish edges and the past; ž rules the middle and the street.

Můžu se na něco zeptat?

Can I ask you something?

Bohužel dnes nemůžu, mám jiný program.

Unfortunately I can't today, I've got other plans.

Můžeme začít, až budeš připravený.

We can start whenever you're ready.

Negation is the prefix ne-: spoken nemůžu, nemůžeš... nemůžou; literary nemohu... nemohou.

moci takes a dependent infinitive

Moci is a modal verb: it does not take a noun object but a dependent infinitive — the action you are or aren't able to do. The infinitive is bare, with no "to"-word in between.

Můžu jít s vámi?

Can I go with you?

Nemůžu najít klíče.

I can't find my keys.

Konečně si můžeme odpočinout.

We can finally rest.

The past tense

The past reverts cleanly to the h-stem and forms the l-participle: mohl, mohla, mohlo, mohli / mohly, plus the auxiliary jsem / jsi / jsme / jste. Note the bare consonant cluster — it is mohl, with no helping vowel, not mohel.

Subject	Participle	First-person example
masc. sg.	mohl	mohl jsem (I could / was able to)
fem. sg.	mohla	mohla jsem
neut. sg.	mohlo	mohlo
masc. anim. pl.	mohli	mohli jsme
fem. pl.	mohly	mohly jsme

Nemohl jsem usnout, byl venku hrozný hluk.

I couldn't fall asleep, there was a terrible noise outside. (male speaker)

Mohli jsme vyhrát, ale udělali jsme hloupé chyby.

We could have won, but we made silly mistakes.

The future tense

Moci is imperfective, so the future is the analytic budu-future, built on the literary infinitive moci (the standard written form here): budu moci, budeš moci... budou moci. In speech, people often sidestep it by using the perfective of the main verb instead, or by saying budu moct.

Až dodělám práci, budu moci přijít.

Once I finish work, I'll be able to come.

The imperative of moci is essentially avoided — "be able to!" makes little sense as a command. To tell someone they're allowed or to invite them, Czech reaches for other verbs (e.g. smět, or just Klidně... "feel free to...").

The conditional: polite requests

The conditional of moci is one of the politest, most useful things you can learn. It combines the h-participle with the conditional auxiliary bych / bys / by / bychom / byste / by, and it is the standard frame for courteous requests — the Czech equivalent of "Could you...?".

Mohl byste mi pomoct?

Could you help me? (addressing a man, formally)

Mohla bys mi půjčit nabíječku?

Could you lend me a charger? (addressing a woman, informally)

Mohli bychom se sejít zítra?

Could we meet tomorrow?

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The participle still agrees with the person you're addressing: Mohl byste...? to a man, Mohla byste...? to a woman. This is the everyday polite-request formula — softer and more natural than the blunt Můžete...? See polite requests for the full toolkit.

moci vs. umět vs. smět

Czech splits English "can" into three verbs, and choosing the right one is essential:

moci / moct — general possibility or circumstance allowing something. Nemůžu přijít = "I can't come" (something's in the way).
umět — a learned skill or know-how. Umím plavat = "I can swim" (I know how). You would never use moci for a skill.
smět — permission. Smím vstoupit? = "May I come in?" (am I allowed?).

Umím řídit, ale dneska nemůžu — nemám auto.

I can drive, but today I can't — I don't have a car.

That single sentence shows the split perfectly: umím for the skill (I know how to drive), nemůžu for the circumstance (no car available today).

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A subtle but important point: the negative nemůžu / nemohu covers both "I can't" (it's impossible) and "I may not" (I'm not allowed) — context decides which. Tady nemůžeš parkovat can mean either "you can't park here" (no space) or "you're not allowed to park here" (it's forbidden). If you need to make "not allowed" explicit, use nesmíš ("you must not / may not").

Common mistakes

❌ Můžu plavat, naučil jsem se to jako dítě.

Wrong verb — for a skill you know, use umět, not moci.

✅ Umím plavat, naučil jsem se to jako dítě.

I can swim, I learned it as a kid. (male speaker)

For an acquired ability, the verb is umět. Moci is for circumstance, not skill.

❌ Včera jsem mohel přijít.

Incorrect — the participle is mohl, with no inserted vowel.

✅ Včera jsem mohl přijít.

Yesterday I could have come. (male speaker)

The masculine participle is the bare cluster mohl, not mohel.

❌ Já mužu přijít.

Incorrect spelling — it's můžu, with ů and ž.

✅ Já můžu přijít.

I can come.

Mind the diacritics: the spoken form is můžu, with the ring over the u (ů) and the háček on the z (ž).

❌ Můžeš mi pomoct?

Grammatical, but blunt as a request to a stranger or superior.

✅ Mohl byste mi pomoct?

Could you help me? (polite, to a man)

Můžeš...? is fine among friends, but for politeness use the conditional Mohl byste...? / Mohla byste...?.

Key takeaways

Two infinitives: moci (literary), moct (spoken) — same verb.
Present alternates h/ž: literary mohu... mohou, spoken můžu... můžou; middle forms (můžeš, může, můžeme, můžete) shared.
Takes a dependent infinitive: Můžu jít?; past reverts to the h-stem: mohl (not mohel).
Future budu moci; imperative is avoided; conditional Mohl/Mohla byste...? = polite "Could you...?".
Distinguish moci (circumstance) from umět (skill) and smět (permission); negative nemůžu covers both "can't" and "may not."

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