Infinitive vs aby-Clause

English lets one little word — to — do an astonishing amount of work: "I want to go," "I want you to go," "I told him to wait." Czech splits these apart with a single, learnable rule. When the person who wants/asks/tries and the person who does the action are the same, Czech uses a bare infinitive (Chci jít "I want to go"). When they are different people, the infinitive is impossible — Czech forces a subordinate clause introduced by aby (Chci, abys šel "I want you to go"). Get this distinction reflexive and a huge range of natural Czech opens up; miss it and you produce sentences no Czech speaker would ever say.

The one rule that governs everything

After verbs of wanting, trying, asking, advising, ordering, allowing, forbidding, fearing — and verbs of purpose generally — Czech asks one question before letting you build the complement:

Is the subject of the second verb the same person as the subject of the main verb?

• Same subject → infinitive. Chci jít. "I want to go." (I want; I go.)
• Different subject → aby + conditional. Chci, abys šel. "I want you to go." (I want; you go.)

This is where English transfer goes badly wrong. English says "I want you to go" with an infinitive that has its own subject ("you"). Czech has no such construction. An infinitive in Czech cannot carry its own subject — so as soon as the doer changes, the infinitive collapses and aby steps in.

Same subject: the bare infinitive

When you do the wanting and you also do the action, the infinitive is exactly right — clean, short, no conjunction.

In every one of these, a single person is doing both verbs. The infinitive simply hangs off the main verb the way it does after a modal.

Different subject: aby + conditional

The instant the second verb has a different doer, you must build an aby-clause. aby is the conjunction a fused with the conditional auxiliary by, so it conjugates for person: abych, abys, aby, abychom, abyste, aby. The verb inside takes the -l participle (the past-tense form), because aby contains a conditional.

Compare the pairs directly and the system clicks into place:

For the full mechanics of aby — how the auxiliary inflects, where it sits, how negation works — see the dedicated aby — purpose and wish clauses page. Here the focus is the choice: infinitive or aby.

Verbs that fall under this rule

The same-subject / different-subject split governs a large, coherent family of verbs. It is worth seeing them grouped, because once you recognize the family you can predict the behavior of a verb you have never met.

Wanting and intending: chtít "to want", přát si "to wish", toužit "to long".

Trying and managing: snažit se "to try", pokoušet se "to attempt", podařit se "to manage". With the same subject these prefer the infinitive; snažit se can also take aby with a different subject, in the causative sense "try to get someone to…".

Asking, advising, ordering, forbidding — these almost always have a different subject (you ask someone else to act), so they overwhelmingly take aby:

Fearing and worrying: bát se "to fear". Same subject → infinitive (Bojím se letět "I'm afraid to fly"); but when you fear that something else will happen, Czech uses aby with negation in its own special way — Bojím se, aby nespadl "I'm afraid he might fall."

Why the infinitive simply cannot take its own subject

The deep reason is structural. A Czech infinitive carries aspect but never person — there is no way to mark who performs it. So in Chci jít, the only available subject is "I", inherited from chci. To say that someone else goes, you need a verb form that can mark person, and that is exactly what the conjugated verb inside an aby-clause provides. English tolerates a "subject" on its infinitive ("I want him to go") because English infinitives are looser; Czech does not, so it reaches for a full clause.

This also explains why even Czech's closest Romance cousins differ: Spanish and French do allow some "want + infinitive with object" patterns, and Latin had the accusative-and-infinitive construction outright. Czech does not. There is no Chci tě jít — that string is simply ungrammatical.

A note on purpose: "in order to"

The same logic extends to purpose. "I'm studying to pass the exam" — same subject (I study, I pass) — can use the infinitive of purpose or, very commonly, abych:

When the purpose involves a different doer, only aby works:

For purpose specifically, aby is usually preferred even with the same subject — the bare "infinitive of purpose" exists but feels terse and is mostly limited to motion verbs (Jdu nakoupit "I'm going to do the shopping").

Common Mistakes

Key Takeaways

• Same subject → infinitive (Chci jít); different subject → aby + conditional (Chci, abys šel).
• The trigger is who does the second action, not the meaning of the main verb — chtít swings both ways.
• A Czech infinitive cannot carry its own subject, so Chci tě jít is impossible. English "want someone to do" always becomes an aby-clause.
• Inside aby, the verb is the -l participle: abys šel, abych pomohl — never the infinitive.
• Verbs of asking, advising, ordering, forbidding almost always mean someone else acts, so they take aby by default.