-е / -у / -о

While the vocative is the canonical grammatical case for addressing someone, its real-world use depends on noun class, accent patterns, and register. Colloquial and urban speech often employs nominative forms instead of inflected vocatives.

1. The ending -е
• Regular masculine nouns ending in hard consonants take -е: брат → брате, Милан → Милане. For foreign masculine personal names, -е is primarily added to stems ending in dental, labial, or nasal consonants (e.g., Роберт → Роберте, Дејвид → Дејвиде, Џон → Џоне), though modern usage equally favors retaining the nominative form (Дејвид!, Роберт!). Names ending in velars (-к, -г, -х) or affricates resist palatalization and do not take -е.
• Triggers palatalization (палатализација) on velars and affricates before -е:
  - к → ч: човек → човече, дечак → дечаче
  - г → ж: друг → друже, бог → боже
  - х → ш: дух → душе
  - ц → ч: отац → оче, стриц → стриче
  - Note that regular masculine stems in -з retain з before -е (мраз → мразе, образ → образе). The shift з → ж is limited to historical titles and specific loanwords such as кнез → кнеже, витез → витеже, and маркиз → маркиже.
• Feminine personal names and female agent nouns ending in -ица systematically take -е: учитељица → учитељице, Милица → Милице.
• Masculine hypocoristic names ending in -ица regularly take -е in standard Serbian, exactly like feminine nouns in -ица: Перица → Перице!, Јовица → Јовице!.
• By contrast, common-gender nouns in -ица allow doublets in both -е and -о: кукавице / кукавицо, пијанице / пијаницо, where the variant in -о carries a stronger pejorative or expressive coloring.

2. The ending -у
• Masculine stems ending in soft/palatal consonants (ј, љ, њ, ћ, ђ, ч, џ, ш, ж) take -у: пријатељ → пријатељу, младић → младићу, муж → мужу, змај → змају, миш → мишу. Foreign names ending in palatals behave similarly: Џорџ → Џорџу.
• Ethnonyms ending in -з (especially in -ез and -уз) regularly take -у: Енглез → Енглезу!, Француз → Французу!, Кинез → Кинезу!.
• Domestic masculine personal names ending in -ш standardly and predominantly take -е (Милоше!, Уроше!, Радоше!), while forms in -у (Милошу, Урошу) function as recognized colloquial or secondary doublets.
• Certain masculine animal names in -ак preceded by dentals or palatals systematically take -у instead of undergoing palatalization to -е, avoiding homophony with young animals: мачак → мачку! (preventing confusion with маче "kitten") and патак → патку! (avoiding паче "duckling").
• Certain foreign names ending in velars take -у to avoid palatalization: Салих → Салиху, Тарик → Тарику.
• Stems ending in -р: regular non-palatal stems take -е (прозор → прозоре, ветар → ветре). By contrast, historically soft stems (like цар → царе!) and agent nouns in -ар (and some in -ир) either take -у or allow variation between -у and -е: господар → господару, лекар → лекару / лекаре, рибар → рибару / рибаре.

3. The ending -о and Nominative Retentions
• Feminine and masculine nouns of the a-declension generally take -о: мајка → мајко, сестра → сестро, судија → судијо.
• Disyllabic personal names in -а with a long-rising tone inflect with -о: Пера → Перо, Јова → Јово, Мара → Маро, Нада → Надо. Conversely, disyllabic names with falling accents (short-falling like Ана!, Маја!, Пеђа!, or unshifted long-falling like Лука!) standardly retain the nominative form in contemporary usage (alongside traditional variants like Луко!).
• Familiar kinship terms like мама, тата, тетка, ујна, and стрина standardly stay identical to the nominative when addressing family members (calling someone стрино or бабо often carries an impolite or pejorative overtone).
• Multisyllabic personal names ending in -а (e.g., female names like Јелена, Марија, and male names like Никола, Немања) standardly retain their nominative forms in contemporary Serbian.
• Foreign masculine names ending in velars (-к, -г, -х) or affricates regularly retain their nominative form (zero ending) in standard direct address to avoid palatalization: Џек!, Марк!, Ерик!, Бах!, as do many other foreign masculine names in modern everyday speech.