aby + Conditional

1. Purpose Clauses
Use aby to explain why an action is done, translating to "so that" or "in order to".

• Učím se, abych rozuměl. (I study so that I understand.)

2. Complement Clauses and Verbs of Motion
When you want, ask, or tell someone else to do something, Czech almost always requires aby (with a few exceptions like nechat). You cannot use an infinitive like in English.

• English: I want you to go.
• Czech: Chci, abys šel. (Literally: I want so that you would go.)

However, for these complement clauses (verbs of wanting, asking, etc.), if the subject is the same, use the infinitive (e.g., Chci jít. = I want to go). Note that general purpose clauses (like in Section 1) often still use aby even with the same subject. Another important rule applies to verbs of motion (like jít or jet): to express purpose when the subject is the same, use a bare infinitive instead of an aby clause (e.g., Jdu nakoupit. = I am going shopping).

3. Forms and Clitics
Because aby contains the conditional auxiliary, it conjugates: abych, abys, aby, abychom, abyste, aby. (Note: In spoken Czech, you will frequently hear the non-standard form abysme instead of abychom, similar to bychom vs bysme. Also, be aware that native speakers often incorrectly write aby jsme or aby jste on the internet, but these are grammatically incorrect spelling mistakes.) It must be followed by the past participle (e.g., dělal, přišla), which must agree in gender and number with the subject of the aby clause (e.g., Chci, abys šel to a man vs. Chci, abys šla to a woman). Do not add another conditional auxiliary like bych.

If the verb is reflexive, the 2nd person singular abys must fuse with the reflexive pronoun: abys + se = aby ses, and abys + si = aby sis. Clitics always go in the second position, immediately after aby. Other object clitics also stack right after aby or its fused forms (e.g., Chci, abys mi to řekl. = I want you to tell it to me).

4. Verbs of Fearing
After verbs like bát se (to be afraid), aby is used with a negated verb to express the fear that something will happen (e.g., Bojím se, aby nespadl. = I am afraid he will fall). Note that using že with a positive verb (e.g., Bojím se, že spadne.) is the everyday default, while aby + negative is a specific, slightly more anxious alternative.

5. Mandatory Comma
In Czech, a comma must always precede subordinate clauses introduced by aby. Unlike English, which often omits the comma before "so that" or doesn't use one with infinitives, you must write it in Czech (e.g., Chci, abys šel.).

6. Independent Clauses
You will also see aby at the beginning of independent clauses (with no main clause) to express wishes, curses, or strong suggestions, as well as in common idioms.

• Aby bylo jasno. (Let's be clear. / Just to be clear.)
• Abys věděl... (Just so you know...)