-у / -и

The locative case (локатив) primarily answers the questions где? (where?) for static location and о коме? / о чему? (about whom? / about what?) for topic or subject matter. Note that in Serbian, locative singular forms are completely identical in endings to dative singular forms.

1. Strict Requirement for Prepositions
Unlike other cases in Serbian, the locative never appears alone without a preposition. In Standard Serbian, it is governed by five primary prepositions:

• у (+ locative): 'in', 'inside', 'at' (enclosed spaces, towns, countries). Example: у стану (in the apartment), у Србији (in Serbia).
• на (+ locative): 'on', 'at' (surfaces, open areas, specific institutions). Example: на столу (on the table), на факултету (at the faculty).
• о (+ locative): 'about' (talking or thinking about someone/something). Example: о филму (about the film), о сврси (about the purpose).
• по (+ locative): 'along', 'around', 'all over'. Example: по граду (around town), по столу (all over the table).
• при (+ locative): 'by', 'near', 'at the time of'. Example: при руци (at hand), при улазу (near the entrance).

2. Singular Endings by Stem Class and Gender

• Consonant-stem masculine nouns: Regular masculine nouns ending in a consonant take -у: град → у граду. If the stem contains a fleeting а (непостојано а) or undergoes vocalization (л → о), the stem adjusts before adding the ending: ветар → на ветру; сто (stem стол-) → на столу; посао (stem посл-) → на послу.
• Neuter nouns: Nouns ending in -о or -е drop their nominative ending and take -у: село → у селу; позориште → у позоришту.
• Feminine nouns ending in -а: Drop -а and add -и: школа → у школи; кућа → у кући. Nouns of the feminine consonant class also take -и: ствар → у ствари.
• Masculine nouns ending in -а: Masculine nouns such as тата, судија, or колега decline like feminine nouns in -а and take -и: о тати, о судији, о колеги.

3. Consonant Alternation (Sibilarization)
When a feminine noun stem ends in к, г, х, these sounds usually shift to ц, з, с before the ending -и:

• к → ц: библиотека → у библиотеци; апотека → у апотеци; рука → у руци.
• г → з: књига → у књизи.
• х → с: сврха → о сврси.

Note: Hypocoristics and proper names (e.g., бака → баки, Милка → Милки) and certain consonant clusters (e.g., тачка → тачки) do not shift.

4. Static Location vs. Motion
Do not confuse static location with destination. To indicate movement towards a goal (answering куда? / where to?), Serbian uses the prepositions у and на with the accusative case instead.