Relative pronoun koji as clause object

In the last lesson koji was always the one DOING something inside its clause: film koji traje tri sata — the film is what lasts. Now look at a different situation: film koji gledam — "the film that I am watching". Here I am the subject of the small clause, and the film is what I watch. Koji now stands for the DIRECT OBJECT of its own clause, and a direct object in Serbian stands in the accusative.

Two decisions, made separately

Every form of koji answers two questions at once, and they come from two different places:

1. Gender and number come from the noun koji refers to (the antecedent), the noun standing right in front of it: film is masculine singular, knjiga feminine singular, pesme plural.
2. Case comes from the job koji does INSIDE its own clause: subject means nominative, direct object means accusative. The main clause has no say in this.

So in Volim glumicu koju gledam the noun glumicu is accusative because it is the object of volim, but koju is accusative for its own reason: it is the object of gledam. In Glumica koju gledam je lepa the antecedent is nominative and koju is still accusative, because inside its clause nothing has changed — I still watch her.

The accusative forms of koji

The pattern is the one you already know from nouns and adjectives. A feminine singular changes -a to -u. Neuter and inanimate masculine look exactly like the nominative, so film koji gledam has the same koji as film koji traje — only the meaning tells you which job it does. In the plural, masculine and feminine share koje, and neuter keeps koja.

The trap is the masculine animate. A person or an animal in the accusative takes the genitive-looking form, exactly as brat becomes brata. So glumac koji glumi (he acts) but glumac kojeg gledam (I watch him). Writing glumac koji gledam is the mistake to watch for: it says the actor is watching, not you. The longer kojega and the shorter kog mean the same and are both correct; in speech you will also hear koga.

Reading the clause

To pick the form, ask who does what inside the small clause. Pesma koju slušam — who listens? I do. The song is listened to, so koju. Pesma koja svira — who plays? The song does, so koja. If the verb after koji already has its own subject (gledam, čitaš, je napisao), koji is almost always the object.

A relative clause can also sit in the middle of the sentence: Knjiga koju čitaš je moja. — "The book you are reading is mine." Serbian puts a comma before the clause only when it adds a side remark about something already identified, so Knjiga koju čitaš je moja has no comma. Notice also that English often drops the pronoun ("the book you are reading"); Serbian never does.