ať / aby

When reporting commands, requests, or instructions, you must pay close attention to syntax and register.

1. Infinitive vs. Subordinate Clause
When reporting commands, requests, or permissions, Czech frequently uses the infinitive even when the subjects are different, especially with verbs like nařídit (to order), zakázat (to forbid), or dovolit (to allow): Lékař mi zakázal kouřit. (The doctor forbade me to smoke.) However, with verbs of communication like říct (to tell) or poprosit (to ask), you must use a subordinate clause with aby or ať: Řekl mi, abych šel. (He told me to go.)

2. Clitic Placement (Crucial Syntax)
Both aby and ať occupy the first position in their clause and act as Wackernagel anchors. This means any unstressed clitics (like se, si, mi, ho) must attach immediately after ať or the inflected form of aby (abych, abys, aby, etc.) in the second position. For example: Řekl mi, ať se nezlobím. (He told me not to be angry.) You can learn more about this in second-position clitics.

3. The 'Ať is only 3rd person' Myth
Beginners often learn ať as a 3rd-person imperative ('let him/them'). However, in reported commands, ať is freely and frequently used for the 1st and 2nd persons as well (e.g., Řekl mi, ať to udělám. - He told me to do it).

4. Mood Changes and the l-participle
Reported commands fundamentally change the mood of the original quote. The original direct quote uses the imperative mood (e.g., Udělej to!), but the reported command changes to present-tense forms (which express future meaning for perfective verbs) with ať (...ať to uděláš) or the conditional with aby. Because aby contains the conditional auxiliary (by), the following verb must be in the l-participle form (e.g., udělal). This forms the conditional mood, which does not inherently carry a past meaning, regardless of the main verb's tense: Řekl mi, abych to udělal.

5. Mandatory Reflexive Contractions and Forms with Aby
When using the 2nd person singular abys with the reflexive pronouns se or si, they must contract. Abys + se becomes aby ses, and abys + si becomes aby sis. For example: Požádal tě, aby ses vrátil. (He asked you to return.) Another massive pitfall for both beginners and native speakers is the 1st person plural: you must use the strictly correct abychom instead of the incorrect aby jsme. While abychom is strictly required in standard written Czech, spoken Czech almost exclusively uses the non-standard abysme, so don't be surprised when hearing native speakers (see standard bychom versus non-standard bysme).

6. Register Matching: Ať vs. Aby
While both conjunctions report commands, they differ in register. Aby is standard and pairs naturally with polite verbs like poprosit (to ask) in formal contexts. Ať is more colloquial and direct, making it better suited for informal commands with verbs like říct (to tell). Using ať with a polite request (e.g., Poprosil mě, ať...) can sound mismatched or overly casual.

7. Choosing the Right Conjunction
Do not confuse reported commands with other types of reported speech. Use že for reported statements (facts), jestli/zda for reported yes/no questions (wh-questions retain their original question words like kdo, co, kde), and aby/ať for reported commands.

8. Negating Aby
When negating a reported command with aby, the negative prefix ne- attaches to the l-participle, never to the conjunction itself. Do not say neabych. For example: Řekl mi, abych to neudělal. (He told me not to do it.)