не + Verb / нисам / немам / нећу

Negation in Serbian is straightforward once you know the division between regular verbal negation and fused negative verbs.

1. Regular Verbal Negation
The negative particle не is placed directly before the verb. This rule applies to finite conjugated verbs as well as infinitives (e.g., не знати) and verbal adverbs (e.g., не знајући). Note that when participles function as descriptive adjectives, they follow the adjective spelling rule and fuse with не- (e.g., непознат, невиђен). Even though verbal не is pronounced together with the following verb as one phonological unit (with stress often shifting forward onto не), it must always be spelled as two separate words:
• не радим (I do not work — never нерадим)
• не видим (I do not see — never невидим)

2. Fused Syntactic Negation
Standard Serbian orthography fuses the negative particle не directly into the verb forms only in four specific verbs (distinct from verbs that carry an inherent lexical prefix):
• нисам (negative present of бити: нисам, ниси, није, нисмо, нисте, нису): Used for identity and descriptions (Ја нисам уморан) and as the auxiliary for the past tense (перфекат, e.g., нисам видео). Non-present forms of бити are written separately (e.g., conditional не бих, future II не будем).
• немам (negative present forms of имати: немам, немаш, нема, немамо, немате, немају): Also appears in the infinitive немати. Note that in standard Serbian, the past tense of имати is negated analytically using the negative auxiliary нисам with the regular participle (нисам имао / имала, није имао). The present forms express lack of possession (немам новца) and existential absence (нема + genitive, meaning 'there is no...').
• нећу (negative present of хтети: нећу, нећеш, неће, нећемо, нећете, неће): Expresses refusal or unwillingness (нећу то) and functions as the auxiliary for negative future statements (негација у футуру I, e.g., нећу радити). Non-present forms are spelled separately (e.g., infinitive не хтети).
• немој (defective negative imperative verb: немој, немојмо, немојте): Used to give negative commands and requests (немој то да радиш).

3. Lexicalized Prefix Verbs
Do not confuse the fused negative verbs above with verbs that contain не- as an inseparable derivational prefix, such as нестати (to disappear) or недостајати (to lack, to miss). In these verbs, не- is part of the dictionary root itself, not the syntactic negation particle не.

4. Double Negation (Negative Concord)
Unlike standard English, Serbian requires negative concord. Words like нико (nobody) or ништа (nothing) must be paired with a negated verb: Нико не зна ('Nobody knows', literally 'Nobody doesn't know').