aby — Purpose and Wish Clauses

English packs an enormous amount into the little word to: "I study to speak Czech," "I want you to come," "tell him to wait." Czech refuses almost all of these infinitives and forces them into a subordinate clause introduced by aby. This one conjunction covers purpose ("so that"), wishes, and reported commands — and it hides a conditional auxiliary inside itself, which is why it changes shape depending on the subject. Master aby and a whole swath of natural Czech opens up.

aby is a + by: it conjugates

aby is not a frozen word. It is the conjunction a ("and / so") welded onto the conditional auxiliary by. Because the auxiliary inflects for person, so does aby — exactly like the present conditional you already know:

The form you pick is governed by the subject of the aby-clause, not by the main verb. After aby the main verb appears as its l-participle (the same one used in the past tense and the conditional), agreeing in gender and number:

Use 1: purpose ("so that / in order to")

The core meaning of aby is purpose: the second clause states the goal of the first. English uses "so that," "in order to," or a bare infinitive of purpose; Czech uses aby.

When the subject of both clauses is the same person, English happily uses an infinitive ("I get up early to catch the train"). Czech still prefers the full aby-clause with a matching person form (abych stihl). There is a competing pattern — a bare infinitive after some verbs of motion (Jdu nakoupit "I'm going to shop") — but for stating purpose with intention, aby is the safe, general choice.

Use 2: reported commands and requests

This is the construction English speakers most often get wrong. After verbs of wanting, asking, telling, begging, advising, requiring, English uses an object + infinitive: "I want you to come," "tell him to wait." Czech cannot do this. It turns the second person into the subject of an aby-clause.

Look closely at Chci, abys přišel. The English "I want you to come" makes "you" the object of "want." Czech makes "you" the subject of the abys-clause — which is exactly why the conjunction is abys (2nd singular), agreeing with the person who is to do the coming, not with "I." The wanter (Chci = I) and the doer (abys = you) are different people, and the clause boundary is where they split.

Use 3: after verbs of fearing, preventing, and taking care

A cluster of verbs about negative outcomes — fearing, preventing, watching out — also takes aby, often with negation. Here Czech is quite logical: you act so that the bad thing does not happen.

Notice aby ses in the second example. Because the verb is reflexive and the subject is 2nd-person singular, the -s of abys fuses with the reflexive: abys + se → aby ses, and abys + si → aby sis. This is the same fusion that gives kdyby ses and by ses, and it is obligatory — never ❌ abys se. The spelling details live on the bys/by spelling page.

Use 4: wishes and "may it be so"

aby can open a standalone wish, like English "May you…" or "(I hope) that…". This is common in toasts, blessings, and curses.

These have the same flavour as the kéž-wishes covered under wishes and preferences with the conditional, but with aby the wish often carries a faint note of warning or purpose.

Word order inside the aby-clause

Within the aby-clause, aby itself takes first position, and any further clitics (reflexive se/si, object pronouns) line up right after it, just as they would after any clause-opener. The l-participle floats to the end.

In aby mi to vysvětlil, the dative mi and accusative to slot in immediately after aby, in the fixed clitic order — the same logic as after bych in second position. And don't forget the comma: a subordinate aby-clause is always set off by a comma in Czech, even where English would omit it.

Common mistakes

Key takeaways

• aby = a
  • the conditional auxiliary by; it conjugates for person: abych, abys, aby, abychom, abyste, aby — chosen by the subject of the aby-clause.
• The main verb after aby is the l-participle, agreeing in gender and number; never add a separate bych.
• It expresses purpose ("so that"), reported commands/requests ("I want you to come" → Chci, abys přišel), fearing/preventing, and wishes.
• English object + infinitive ("want you to come," "tell him to wait") becomes a Czech aby-clause, not an infinitive.
• 2nd-person singular + reflexive fuses: aby ses, aby sis. Always set the clause off with a comma. For the broader family of conditional subordinators, see aby and kdyby clauses.