Understanding the difference between koji and što is one of the most common hurdles for non-native speakers learning Croatian, Serbian, or Bosnian. Both often translate to “which,” “that,” or “who” in English, but they are not always interchangeable.
Mastering Koji vs Što comes down to three main rules: identifying whether you are describing, determining, or referring to an entire sentence.
Table of Contents
Rule 1: Describing vs. Determining
1. Describing (Extra Information) → Use KOJI
When you are simply adding extra detail about a noun without trying to separate it from a group, koji is your only option.
- Example: Moj brat, koji je vozač taksija, me planira posjetiti.(My brother, who is a taxi driver, plans to visit me.)
- Why: You are giving additional info about your brother, not singling him out from a list of brothers. Što cannot be used here.
2. Determining (Specific Selection) → Use KOJI or ŠTO
When you need to single out a specific person or object from a group (“the one that…”), you can use either word, though koji remains more common.
- Example: Vidjela sam tvoju prijateljicu koja ide sa mnom na fakultet.
- Alternative: Vidjela sam tvoju prijateljicu što ide sa mnom na fakultet.
Pro-Tip: Pairing što or koji with demonstrative pronouns (taj, onaj) makes determining sentences sound much more natural and prevents confusion with causal što (e.g., “Tužan sam što nisi došla” = I am sad because you didn’t come).
- Example: Daj mi tu knjigu što stoji na stolu.
Rule 2: Case Declensions and Pronoun Insertion with Koji vs Što
Because koji changes based on gender, number, and case, it naturally handles complex grammar. If you swap koji for što in a non-subject role, you must add an extra pronoun to signal the case.
| Structure | Example Sentence | Meaning |
| Using Koji | Jesam li ti pričala o onoj ženi koju sam vidjela ranije? | Did I tell you about the woman I saw earlier? (the woman is the object = accusative) |
| Using Što (+ pronoun) | Jesam li ti pričala o onoj ženi što sam je vidjela ranije? | Did I tell you about the woman I saw earlier? |
| Subject Exception | Došao je onaj čovjek što puno priča. | The man who talks a lot arrived. (No extra pronoun needed, the man is the subject) |
Genders, cases, numbers… If you want to learn more about the basic Bosnian grammar and don’t know where to start, check out my free guide here!
Rule 3: Word vs. Whole Sentence
What does your relative pronoun refer back to?
- Referring to a specific noun: Use koji.
- Onaj poštar je došao, koji me je usrećio. (The mailman—the specific guy who makes me happy—came.)
- Referring to an entire action/clause: Use što.
- Poštar je došao, što me je usrećio. (The fact that the mailman came is what made me happy.)
The Absolute Exception: Indefinite Pronouns
There is one major scenario where koji fails and što is strictly required. After indefinite or neutral pronouns (ono, sve, nešto, ništa, to), always default to što:
- Ono što želim je mir. (What I want is peace.)
- Sve što kažeš je istina. (Everything you say is true.)
- Ništa što si rekao nema smisla. (Nothing you said makes sense.)
(Note: If the pronoun takes a specific preposition/case, decline što accordingly: “Nisi mi rekao ništa o čemu nisam već razmišljala.”)
If you’re not familiar with those pronouns, I recommend reading this post about demonstrative pronouns in Bosnian.
Quick Summary Cheat Sheet
- Giving extra context? Use Koji.
- Referring to an entire sentence’s action? Use Što.
- Following sve, ništa, nešto, ono, to? Use Što.
- Picking one specific item out of many? Use Koji (or Što + pointer word).
- In doubt? Koji is almost always the safer bet.
Which of these rules do you find trickiest to put into practice when speaking?
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Practice Exercise: Test Your Knowledge
Choose between koji (in its correct form) or što to complete each sentence. Find your answers below.
- Sve __________ si mi kupio je predivno! (Everything that you bought me is beautiful!)
- To je čovjek __________ sam sreo jučer na ulici. (That is the man whom I met yesterday on the street.)
- Pao je snijeg, __________ je iznenadilo sve vozače. (It snowed, which surprised all the drivers.)
- Moj susjed, __________ radi u bolnici, kupio je novi auto. (My neighbor, who works in the hospital, bought a new car.)
- Imaš li nešto __________ mi može pomoći? (Do you have something that can help me?)
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Answer Key & Explanations
- što — Follows the indefinite pronoun sve (Rule: sve + što).
- kojeg — Refers to a specific masculine noun (čovjek) serving as an object in the accusative case.
- što — Refers to the entire preceding action/sentence (Pao je snijeg), not a single noun.
- koji — Provides extra descriptive detail about the neighbor without singling him out from a group.
- što — Follows the indefinite pronoun nešto.
Can I always use koji instead of što to stay safe?
Almost always, but not after indefinite pronouns (sve, ništa, nešto, ono, to). In those specific cases, using koji is grammatically incorrect.
Why do native speakers sometimes use što when koji seems more appropriate?
In everyday spoken Bosnian, što is often used as a casual, invariant relative pronoun for specific nouns (e.g., “čovjek što sam ga vidio”). While widespread in casual speech, this requires adding extra personal pronouns (ga, je, im) and is generally avoided in standard written Bosnian.
How do I know which case form of koji to use (koji, kojeg, kojem)?
Gender and number come from the noun you are describing, but the case comes from the job koji does inside its own clause (subject = nominative koji, direct object = accusative kojeg, indirect object = dative kojem).
How does a preposition affect koji vs. što?
Prepositions must directly attach to a word that changes cases. Because koji inflects, it pairs with prepositions (e.g., u kojem, s kojim). Invariable što cannot pair with prepositions directly unless declined into forms like čemu or čime.