Mistake: Subtle Preposition and Case Mismatches

The blunt preposition errors fade after A2 — most learners stop saying *u grad for "in town." What survives into B2 is a set of finer mismatches: two prepositions that look interchangeable but split by meaning, a case flip you keep forgetting under na, a preposition whose government you half-remember, and the days of the week. These are the errors that still mark otherwise-fluent speech. This page collects them as wrong→right pairs, each with the governing rule. The basics are on the case-after-prepositions page; here we go one layer deeper, into the abstract prepositions.

zbog (cause) vs radi (purpose)

Both translate loosely as "because of / for the sake of," and both take the genitive, so the case is not the issue — the meaning is. zbog names a cause (why something happened); radi names a purpose (what something is aimed at). Using radi for a cause is the persistent error, because English "because of" pushes you toward whichever word you learned first.

na + location is the locative, not the accusative

You learned the motion/rest flip at A2, but it keeps slipping with na + abstract or institutional places (fakultet, posao, more). Being at university is rest → locative (na fakultetu). The error is leaving the noun in the accusative fakultet, the motion form, when no motion is involved.

The accusative na fakultet is correct only with motion: idem na fakultet ("I'm going to university"). State, location, "being there" → locative.

kod always takes the genitive

Kod ("at someone's place / at the …'s") governs the genitive — full stop, in every meaning. The error is to slip into the dative because English "to the doctor" feels like a direction, or because idem (a motion verb) tempts you toward another case. Kod never bends: genitive every time.

Note that kod covers both "going to someone's place" and "being at someone's place" with the same genitive — unlike u/na, it does not flip with motion. The motion is expressed by the verb; kod itself is invariant.

Transport is the bare instrumental — drop the s

The means of transport takes the bare instrumental with no preposition: vlakom, autom, autobusom. Adding s ("with") turns the vehicle into a travelling companion. This is a known A2 point, but it resurfaces at B2 with less common vehicles and in writing, where the s creeps back in by analogy with English "by."

The s + instrumental is reserved for genuine company (putujem s prijateljem — "I'm travelling with a friend"), never for the vehicle.

Days of the week are the accusative, not the locative

"On Monday" tempts the locative (it feels like a "time when," and u + locative marks many time expressions). But a day of the week after u takes the accusative: u ponedjeljak, u srijedu, u petak. The locative u ponedjeljku is wrong for "on Monday."

Compare months and years, which DO take u + locative (u srpnju — "in July," u ovoj godini — "this year"). The accusative is specific to days of the week and to clock-time-ish expressions; the locative covers the larger units. This split is exactly the kind of detail that distinguishes a B2 speaker from a fluent one.

Key Takeaways

• zbog (cause) vs radi (purpose) — both + genitive, but zbog kiše = "because of rain," radi posla = "for the sake of work." Don't use radi for a cause.
• na + location = locative (na fakultetu, na moru) for rest; the accusative (na fakultet) is only for motion. The flip keeps slipping at B2 with institutions and abstract places.
• kod always takes the genitive (kod doktora, kod bake) — in every meaning, motion or rest; it never bends to the dative.
• Transport is the bare instrumental (vlakom, autom) — no s; the s
  • instrumental is for human company only.
• Days of the week are accusative after u (u ponedjeljak, u srijedu); months and years take the locative (u srpnju). Days are targets, not containers.