The Infinitive: -t, -ti, -ci

When you look a Czech verb up in a dictionary, the form you'll find is the infinitive — the verb's "name," stripped of any person, tense, or gender. dělat ("to do"), mluvit ("to speak"), číst ("to read"): these are the citation forms, and they are where every conjugation table begins. The infinitive is the neutral, uninflected shape of the verb, and learning to recognise it instantly is the foundation for everything that follows.

The good news for English speakers is that the infinitive is one of the few places where Czech is simpler than your language, not harder. English uses a two-word infinitive — the particle to plus the verb (to read, to work). Czech has no such particle at all. The whole infinitive is a single word, and the "to" is baked into the ending. Where English says to read, Czech says simply číst.

The thing to keep in mind from the very start is that the infinitive carries aspect but nothing else. dělat is the imperfective infinitive and udělat the perfective one — two different infinitives for the same English "to do." But neither one tells you who is doing it, when, or in what gender. Those are added later by conjugation. The infinitive is the pure lexical idea of the verb, marked only for whether the action is viewed as a process or as a finished whole.

The three infinitive endings

-t — the everyday ending

The overwhelming majority of Czech verbs end in -t. This is the form you will meet thousands of times and the one you should treat as the default.

-ti — the literary and archaic variant

You will occasionally come across infinitives ending in -ti instead of -t: dělati, mluviti, býti. This is an older form, now (literary) or (archaic): you'll see it in the King James-style register of older books, in poetry, in legal and ceremonial language, and frozen into a few set phrases. In modern speech and ordinary writing it is always -t. You should be able to recognise -ti when you read it, but never produce it in everyday Czech.

-ci — a small, irregular group

A handful of high-frequency verbs end in -ci (sometimes spelled -ct colloquially). The most important are:

These are genuinely irregular and you simply have to memorise them. There is no productive rule that generates new -ci verbs — the group is closed and small. In informal speech you will often hear říct for říci and moct for moci; both colloquial (informal) variants are completely standard in conversation.

What the infinitive is used for

After modal and phase verbs

This is the infinitive's bread-and-butter job. Modal verbs (can, must, want, may) and phase verbs (begin, continue, stop) take a second verb in the infinitive. This is exactly parallel to English I want to go, except there's no to.

Notice that the modal verb takes all the grammatical work — musím is "I must," first person — and the infinitive stays uninflected: pracovat, not a conjugated form. Only one verb in the chain gets conjugated; the other stays in the infinitive.

As the complement of many verbs

Beyond the modals, a large set of ordinary verbs take an infinitive complement: učit se ("to learn to"), umět ("to know how to"), zapomenout ("to forget to"), bát se ("to be afraid to"), and many more.

As a subject-like complement

The infinitive can behave almost like a noun, naming an activity that the sentence then says something about. English does the same with to + verb or -ing: to learn is important / learning is important.

In impersonal constructions

Czech uses the infinitive in many impersonal phrases — instructions, questions, offers — where English would need a full clause with a subject.

A warning that pays off later: the infinitive stem ≠ the present stem

It is tempting to assume that if you know the infinitive, you can predict every other form just by chopping off the ending. For many verbs that works — but for an important class it does not, and being aware of this now will save you confusion later. Some verbs build their present tense on a different stem from the infinitive.

The classic example is nést ("to carry"). The infinitive stem looks like nés-, but the present tense is nese-: nesu, neseš, nese, not anything based on nés-. The infinitive and the present run on two different stems of the same verb.

There's no clean shortcut here: which verbs have a divergent present stem is something you absorb class by class as you work through the present-tense pages. The point for now is simply to expect it, so that when nést turns into nesu you recognise it as normal Czech and not a typo.

Common Mistakes

Key Takeaways

• The infinitive is the dictionary form, ending almost always in -t (dělat, mluvit, číst).
• -ti is literary/archaic (recognise only); -ci marks a small irregular group (moci, říci, péci).
• The infinitive carries aspect (dělat vs udělat) but no person, tense, or gender.
• Czech has no "to" particle — the infinitive is a single word.
• It is used after modal and phase verbs, as a verb complement, as a subject-like phrase, and in impersonal constructions.
• The infinitive stem is not always the present stem (nést → nesu), so learn the present form separately.