biti

Biti is the infinitive of the verb “to be” in the South Slavic languages used in Bosnia and Herzegovina, Croatia, Serbia, and Montenegro. It is an irregular and highly frequent verb, functioning both as a copula (linking subject and predicate) and as an auxiliary in perfect and passive constructions. It also appears in a variety of idiomatic expressions and set phrases.

Etymology and cognates: Biti derives from Proto-Slavic *bytь and is cognate with Russian быть, Polish być, and Czech být. The core meaning is existence or identity, and it provides the grammatical backbone for tense, mood, and voice in these languages.

Conjugation and forms:

- Present indicative: sam, si, je, smo, ste, su (though emphatic forms like jesam, jesi, jeste are found in some speech and stylistic contexts).

- Past tense: typically formed with the present of biti plus a past participle. Examples: ja sam bio (masc), ja sam bila (fem), ono je bilo (neuter); mi smo bili/bile; vi ste bili/bile; oni su bili (masc), one su bile (fem).

- Past participle: bio, bila, bilo; bili, bile, bila, with exact form depending on gender and number.

- Future: two common options. Periphrastic: ja ću biti, ti ćeš biti, on/ona/ono će biti, mi ćemo biti, vi ćete biti, oni će biti. Short future forms also occur in common use: biću, bićeš, biće, bićemo, bićete, biće.

Usage notes:

- Biti as a copula does not require agreement with a predicate adjective in some tenses; the predicate typically agrees in form with the subject.

- As an auxiliary, biti forms the passive voice in combination with a past participle (e.g., knjiga je napisana, “the book was written”).

Biti is foundational across the standard varieties and features notable dialectal variation in mood and aspect.