Ovo je daska koju merimo mernom trakom.

this

Breakdown of Ovo je daska koju merimo mernom trakom.

• biti: to be
• koji: that (relative pronoun)
• meriti: to measure

Questions & Answers about Ovo je daska koju merimo mernom trakom.

What is the role of koju here, and why is it koju instead of koja?

Koju is the relative pronoun which/that introducing the clause koju merimo mernom trakom.

Why koju?

• It refers back to daska.
• Daska is feminine singular, so the relative pronoun must also be feminine singular.
• Inside the relative clause, it is the direct object of merimo (we measure), so it takes the accusative case.

So:

• nominative feminine singular: koja
• accusative feminine singular: koju

That is why Serbian uses koju, not koja.

Why is daska in the nominative, but koju is not?

Because they have different jobs in the sentence.

• Daska is part of the main clause: Ovo je daska = This is a board/plank.
  • Here daska is the predicate noun after je, so it appears in the nominative.
• Koju belongs to the relative clause: koju merimo mernom trakom = which/that we are measuring with a measuring tape
  • In that clause, koju is the object of merimo, so it is in the accusative.

So even though refers to , its case is determined by its function in its own clause.