Uses of the Infinitive | Czech Grammar

The infinitive is the verb's "name tag" — the form you find in the dictionary (dělat, jít, číst) — and it does a surprising amount of work in real sentences. It cannot stand as the main verb of a clause on its own, but it slots in after modals, after phase verbs, as a complement to dozens of ordinary verbs, and even as the subject of a sentence. One thing it never does is carry a person or a tense; it does, however, carry aspect, so you still choose between the imperfective and perfective member. This page walks through its principal uses — and the crucial moment when Czech makes you drop the infinitive and switch to an aby-clause instead.

First, the shape

The infinitive ends in -t for almost every verb (dělat, psát, mít), with a small set ending in -ct/-ci (moct/moci, péct/péci) and the archaic literary variant in -ti (dělati, found only in old texts). Whatever the ending, the key fact is that it is invariable: it never changes for person, number, or tense. And unlike English, there is no "to" particle — Czech jít alone means "to go."

Chci spát, jsem úplně vyčerpaný.

I want to sleep, I'm completely exhausted.

This is the infinitive's most frequent home. Modal verbs (chtít want, muset must, moct can, smět may, umět know how to) and phase verbs (začít/začínat begin, přestat/přestávat stop, zůstat stay) are followed directly by a bare infinitive — the action they frame.

Musím jít, mám za chvíli vlak.

I have to go, I've got a train soon.

Začínám chápat, jak to funguje.

I'm beginning to understand how it works.

Přestaň křičet, slyším tě dobře.

Stop shouting, I can hear you fine.

Venku začalo pršet, vezmi si deštník.

It started raining outside, take an umbrella.

Note začalo pršet: the phase verb začít carries the tense and the neuter agreement, while pršet ("to rain") stays in the bare infinitive. For the full inventory of these verbs and the aspect they prefer, see the infinitive after modals and phase verbs.

As a complement of many ordinary verbs

Well beyond the modals, a long list of everyday verbs take an infinitive as their complement — verbs of learning, trying, daring, fearing, intending, and so on. The infinitive names the action involved.

Verb	infinitive	Meaning
učit se	učit se plavat	to learn to swim
bát se	bát se létat	to be afraid to fly
zkusit	zkusit to opravit	to try to fix it
snažit se	snažit se zhubnout	to try to lose weight
potřebovat	potřebovat si odpočinout	to need to rest

Učím se plavat, ale jde mi to pomalu.

I'm learning to swim, but it's slow going.

Bojím se létat, radši jezdím vlakem.

I'm afraid to fly, I'd rather take the train.

As subject or predicate

An infinitive can be the subject of a sentence — naming an activity in the abstract — typically with an impersonal predicate like je těžké ("it's hard"), je zakázáno ("it's forbidden"), or je čas ("it's time"). English does the same with the gerund ("Smoking is forbidden") or a "to"-infinitive ("It's hard to understand").

Kouřit je tu přísně zakázáno.

Smoking is strictly forbidden here.

Je těžké to pochopit napoprvé.

It's hard to understand it the first time.

Je čas jít spát.

It's time to go to sleep.

It can also stand in predicate position, often after a copula, naming what something amounts to or aims at:

Mým snem je cestovat kolem světa.

My dream is to travel around the world.

In fixed impersonal expressions

Czech uses a bare "deliberative" infinitive in a set of fixed, subjectless questions and exclamations — the equivalent of English "What to do?", "Where to go?". There is no subject and no finite verb; the infinitive carries the whole thought.

Co dělat, když nikdo neodpovídá?

What to do when nobody answers?

Kam jít na dobrý oběd v centru?

Where to go for a good lunch downtown?

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These bare-infinitive questions feel slightly rhetorical or musing — you're weighing options aloud. To ask a concrete "what should I do?", Czech adds a modal: Co mám dělat?

The big fork: infinitive vs. aby-clause

Here is the point that catches every learner. Some verbs of wanting, asking, and telling take an infinitive — but only when the doer of the second action is the same as the subject of the first. The moment the doer changes, Czech cannot use an infinitive and must switch to an aby-clause (a subordinate clause with aby + a past-tense form).

The principle is clean:

Same subject → infinitive. Chci jít. — "I want to go" (I want, I go).
Different subject → aby-clause. Chci, abys šel. — "I want you to go" (I want, you go).

Chci jít domů, jsem unavená.

I want to go home, I'm tired. (same subject → infinitive)

Chci, abys šel domů, je pozdě.

I want you to go home, it's late. (different subject → aby-clause)

Prosím tě, abys mi zavolal.

I'm asking you to call me. (different subjects → aby; note the comma)

This is where English misleads you. English says "I want you to go" with what looks like an infinitive ("to go"), so learners reach for Chci tě jít — which is simply not Czech. When the subjects differ, you must use aby. The whole comparison, including the comma rules, is on infinitive vs. aby-clause; the conjunction itself is on aby.

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The infinitive has no subject of its own, so it can only ever mean "the same person again." That single fact explains the whole rule: if you need to name a different doer, the infinitive physically can't hold that information — so Czech reaches for a full clause with aby.

Aspect, but no tense

Because the infinitive carries aspect, you still choose a member of the aspect pair, and the choice colours the meaning even with no tense of its own:

Musím si přečíst tu zprávu.

I have to read that report (all the way through). (perfective — get it done)

Večer rád čtu.

In the evening I like to read. (imperfective — the activity)

Common Mistakes

❌ Chci ty jít domů.

Incorrect — different subjects can't share an infinitive; use an aby-clause.

✅ Chci, abys šel domů.

I want you to go home.

❌ Chci jdu domů. (conjugating the second verb instead of leaving it as an infinitive)

Incorrect — after chtít the second verb must be a bare infinitive, not a finite form; say jít, not jdu.

✅ Chci jít domů.

I want to go home.

❌ Musím k jít. (inserting a 'to' particle)

Incorrect — Czech has no 'to' before the infinitive; jít stands alone.

✅ Musím jít.

I have to go.

❌ Začalo pršelo. (a finite verb after the phase verb)

Incorrect — a phase verb takes an infinitive, not another tensed verb.

✅ Začalo pršet.

It started raining.

Key Takeaways

The infinitive ends in -t (some in -ct/-ci); it carries aspect but no person or tense, and takes no "to" particle.
Its main jobs: after modal/phase verbs, as a complement of many verbs (učit se plavat, bát se létat), as subject/predicate (Kouřit je zakázáno), and in fixed impersonal questions (Co dělat?).
Same subject → infinitive (Chci jít); different subject → aby-clause (Chci, abys šel).
English "want you to go" looks like an infinitive but must become aby in Czech.

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