Ja sam juče poslala pismo prijateljici.

I sent a letter to a female friend yesterday.

Breakdown of Ja sam juče poslala pismo prijateljici.

• ja: I
• prijateljica: female friend
• juče: yesterday
• pismo: letter

Questions & Answers about Ja sam juče poslala pismo prijateljici.

Why is Ja included? I thought Serbian often drops subject pronouns.

Yes, Serbian often drops subject pronouns because the verb already shows the person.

So Ja sam juče poslala... can often be shortened to:

Juče sam poslala pismo prijateljici.

Including ja usually adds a little emphasis or contrast, like:

• I sent the letter yesterday.
• I was the one who sent it.

So ja is not wrong at all—it just is not always necessary.

What does sam mean here?

Sam is the 1st person singular present form of biti (to be), and here it is used as an auxiliary verb to form the past tense.

So the past tense here is built like this:

• sam = auxiliary
• poslala = past participle

Together:

• sam poslala = I sent

This is the normal way Serbian forms the past tense.

Why is it poslala and not poslao?

Because poslala shows that the speaker is female.

In Serbian past tense, the participle agrees with the subject in gender and number.

For ja:

• male speaker: