Ostavila sam ključ na stolu.

I left the key on the table.

Breakdown of Ostavila sam ključ na stolu.

• biti: to be
• sto: table
• na: on
• ključ: key

Questions & Answers about Ostavila sam ključ na stolu.

Why is it ostavila and not ostavio?

Because the speaker is female.

In Serbian past tense, the main verb agrees with the gender and number of the subject:

• ostavila sam = I left (said by a woman)
• ostavio sam = I left (said by a man)

So ostavila sam ključ na stolu is something a woman would say.

What does sam do here?

Sam is the 1st person singular form of the auxiliary verb biti (to be) used to form the past tense.

So the past tense here is built like this:

• ostavila = past participle
• sam = I am auxiliary, which helps make the past tense

Together:

• ostavila sam = I left

This is a very common Serbian past-tense pattern.

Why isn’t there a word for I in the sentence?

Because Serbian often drops the subject pronoun when it is already clear from the verb form.

Here, sam already tells you the subject is I, so ja is unnecessary.

• Ostavila sam ključ na stolu. = normal, natural
• = also correct, but adds emphasis to