aby: Purpose and 'want someone to'

aby is one of the busiest words in Czech, and one of the trickiest for English speakers because it does two things that English handles with completely different grammar. It expresses purpose ("so that / in order to") and it introduces the complement of verbs of wanting, asking, advising, and fearing ("I want you to come"). What makes it hard is not the meaning but the form: aby fuses conditional person-endings onto itself — abych, abys, aby, abychom, abyste, aby — and is followed by the l-participle, never a present-tense verb. Master that pattern and a huge slice of Czech subordinate syntax opens up.

The forms: aby carries the person

Just like kdyby, aby is a conjunction with the conditional auxiliary baked in, so it changes shape for person. The verb after it appears as the l-participle (the same form used in the past tense), not the present or infinitive.

The endings are exactly the conditional set (-bych, -bys, -by, -bychom, -byste, -by) glued to a-. If you already know the present conditional, you already know how to inflect aby.

Use 1: Purpose — "so that / in order to"

aby answers the question Proč? / Za jakým účelem? ("Why? / To what end?"). It links an action to the goal behind it.

Here is a key subtlety English speakers miss. When the purpose has the same subject as the main clause ("I study so that I can…"), Czech can still use aby (matched to that subject) — but for many verbs it prefers a plain infinitive of purpose, especially after motion verbs:

The rule of thumb: same subject → infinitive is often smoother; different subject → aby is obligatory. For the full decision, see infinitive vs aby-clause.

Use 2: After verbs of wanting, asking, advising — the big trap

This is where English grammar actively misleads you. In English, "I want you to go" uses an object + infinitive (linguists call it an ECM or raising structure). Czech has no such construction. You cannot say "chci tě jít." When the wanting-verb and the desired action have different subjects, Czech forces an aby-clause:

Compare the same-subject case, where you do use an infinitive because there is only one subject:

So the split is clean: same subject → infinitive (chci přijít); different subject → aby (chci, abys přišel). This same pattern covers a whole family of verbs — asking, advising, insisting, and so on:

Verbs of telling someone to do something turn a command into an aby-clause — the Czech way of doing reported commands, covered on the reported speech page.

Use 3: After verbs of fearing — with negation

Verbs of fearing (bát se, obávat se) take aby too, and here Czech does something that surprises English speakers: the aby-clause is negated even though the meaning is positive worry. "I'm afraid he'll fall" comes out as bojím se, aby nespadl — literally "I'm afraid that he not fall," i.e. "I hope he doesn't fall / I fear he might fall."

The logic is that you are stating the outcome you are trying to avoid, so the clause names the thing you don't want to happen. It feels backwards at first, but it is fully regular after fearing-verbs.

Aspect and word order inside the aby-clause

Because aby takes the l-participle, you still choose aspect — perfective for a completed goal, imperfective for an ongoing one — just as in the past tense. And clitics inside the aby-clause still obey second position, but note: aby itself counts as the first slot, so a reflexive se/si or a short pronoun clings right after it: aby *se to naučil, abych **ti pomohl*.

Common Mistakes

Key Takeaways

• aby fuses the conditional person-endings: abych, abys, aby, abychom, abyste, aby, followed by the l-participle — never a present or infinitive.
• Purpose ("so that / in order to"): Učím se, abych uměl česky. Same subject often prefers the infinitive; different subject requires aby.
• Wanting / asking / advising with a different subject forces aby — English "I want you to go" is Chci, abys šel, with no infinitive available.
• Fearing verbs take a negated aby-clause: Bojím se, aby nespadl = "I'm afraid he'll fall."
• The comma before aby is obligatory, and a following clitic (se/si, short pronoun) hugs aby: aby se to naučil.