Questions & Answers about Njegova knjiga je stara.
Why is it Njegova knjiga and not Njegov knjiga?
Croatian possessive pronouns agree in gender, number, and case with the noun they modify — not with the possessor. Since knjiga (book) is feminine singular, you must use the feminine form njegova, even though njegov is the masculine form.
Why does the adjective end with -a in stara?
Adjectives in Croatian also agree with their nouns in gender, number, and case. Here stara is in the nominative singular feminine form to match knjiga, which is a feminine noun.
What case is knjiga in, and how do I recognize it?
knjiga is in the nominative singular case — that’s the base form of a noun used for the subject of a sentence. You recognize it by its ending -a (typical for many feminine nouns in the nominative singular) and by the fact that it’s the subject of je stara.
Why is the verb je needed here? Can I say Njegova knjiga stara?
je is the third-person singular present tense of the verb biti (to be) and functions as a linking verb. In standard Croatian you need je for “X is Y.” Omitting je would be ungrammatical (or at best colloquial in certain dialects).