sebe

The full reflexive pronoun does not have a nominative form and never changes for person, gender, or number. It only changes based on the grammatical case required by the sentence:

• Genitive / Accusative: sebe (se)
• Dative: sobě (si)
• Locative: sobě
• Instrumental: sebou

1. After Prepositions (Mandatory)
You cannot put short clitics after a preposition. You must always use the full form. Note that se is the short form of sebe (Genitive/Accusative) and si is the short form of sobě (Dative). For example, mluvit o sobě (to talk about oneself) or udělat to pro sebe (to do it for oneself).

2. Spatial Prepositions (English Interference)
In English, personal pronouns are used for spatial relationships referring to the subject (e.g., "behind you", "around him"). However, Czech strictly requires the reflexive pronoun when the object refers back to the subject. For example, use za sebou (behind oneself), kolem sebe (around oneself), před sebou (in front of oneself), or vedle sebe (next to oneself).

3. Emphasis and Contrast
When you want to contrast "oneself" with someone else, you use the full form. For example: Vidím sebe, ne tebe. (I see myself, not you.)

4. Accompaniment (s sebou)
When taking something "with you" or having something "on you", Czech uses the preposition s + the instrumental form sebou for all persons (e.g., Mám s sebou peníze. - I have money with me). Note the spelling: the Czech Language Institute dictates it is written s sebou (not se sebou) when expressing accompaniment, such as ordering coffee "to go" (káva s sebou). Because it is pronounced together as a single word ([sebou] or [ssebou]), it is often misspelled even by native speakers.

5. Other Instrumental Uses (se sebou / sebou)
The choice between se sebou and the bare instrumental sebou depends purely on the grammatical valency (case government) of the specific verb or adjective. If the word requires the preposition s, you use se sebou (e.g., být spokojený se sebou - to be satisfied with oneself). If the word governs the bare instrumental case, you use sebou (e.g., být si jistý sám sebou - to be sure of oneself). The bare instrumental is also used for sudden physical movements (e.g., trhnout sebou - to flinch) and in fixed idioms (e.g., to se rozumí samo sebou - that goes without saying).

6. Reciprocity (Each Other)
In the plural, the full reflexive pronoun is frequently used to express reciprocity ("each other" or "one another"). For example: mluvit o sobě (to talk about each other) or bavit se mezi sebou (to chat among themselves).