чега / чему / чиме

When asking questions about inanimate things, the standard interrogative pronoun in contemporary Serbian is шта for the nominative and accusative. However, for all oblique cases (genitive, dative, locative, and instrumental), it inflects using the stems че- and чи-. These oblique forms (чега, чему, чиме) directly preserve the ancient Slavic stem, whereas шта developed later in the nominative/accusative.

In contemporary standard Serbian, the base form шта is used in the accusative case, including when governed by prepositions: e.g., За шта је ово? (What is this for?), На шта мислиш? (What do you have in mind?). Note that in modern Serbian, што primarily functions as an interrogative adverb meaning why (synonymous with зашто; e.g., Што не спаваш?) or as a relative conjunction (што), rather than as the object pronoun after prepositions.

For the other cases, you must use the declined oblique forms:

1. Genitive: чега
Governed by prepositions such as од (from/of), без (without), пре (before), or verbs that take genitive complements such as плашити се (to fear).
Example: Од чега је направљен овај колач? (What is this cake made of?)

2. Dative and Locative: чему
In standard Serbian, the dative and locative pronouns share the form чему, but they follow fundamentally different syntactic rules:

• Locative: Crucially, the locative can never appear on its own without a preposition. It is always triggered by a preposition such as о (about), по (according to / after), or у (in). For example: О чему размишљаш? (What are you thinking about?).
• Dative: Unlike the locative, the dative can appear bare (without any preposition) when asking about purpose, function, or rhetorical futility (e.g., Чему служи ова алатка? – What does this tool serve? / What is it used for?; Чему све ово? – What is all this for?), or as a verbal complement (e.g., радовати се чему, чудити се чему). Directional inquiries use adverbs like куда or prepositional phrases (ка чему).

3. Instrumental: чиме (or чим)
Used to ask about the instrument, means, or method used to complete an action. When asking about an instrument or means of transportation, Serbian uses the bare instrumental without prepositions: Чиме путујеш? (What do you travel by / By what means do you travel?).
The longer form чиме is heavily preferred—especially at the beginning of a question—to avoid confusion with the temporal conjunction чим (meaning as soon as). The shorter form чим is occasionally heard in casual speech within prepositional phrases (e.g., С чим иде овај сос?).
The preposition са is used when asking about accompaniment, addition, or ingredients (e.g., Са чиме једеш палачинке? – What do you eat pancakes with?). Other prepositions can also govern the instrumental pronoun depending on spatial or relational nuances, such as под (Под чиме?) or за (За чиме чезнеш? – What are you longing for?).

4. Word Order: Preposition Fronting
Serbian strictly forbids preposition stranding (leaving a preposition at the end of a sentence like in English). The preposition must always stand directly before the pronoun: О чему причате? (never *Шта причате о?).