Learn Hardcore Croatian: Jučer sam već bio poslao životopis, ali sam ga morao promijeniti prije roka. - Yesterday I had already sent the CV, but I had to change it before the deadline.

So in your sentence, the pluperfect emphasizes that the sending of the CV was already completed before some other past reference point (the need to change it before the deadline).

In everyday speech, Croatians often just use the perfect (sam poslao) and let context or words like već (already) show that the action was earlier, but the pluperfect is still correct and used, especially in writing or when you want to be very clear about the sequence of past events.

Are sam and bio both forms of biti (to be)? Why do we need both?

Yes, both come from biti (to be), but they have different grammatical roles here:

sam = present tense auxiliary of biti, 1st person singular (I am).
bio = past participle (so‑called l‑participle) of biti (been).

In the pluperfect, Croatian uses two pieces from biti plus the past participle of the main verb:

sam (present of biti) + bio (l‑participle of biti) + poslao (l‑participle of poslati).

So structurally:

ja sam bio poslao = I had sent
literally: I am been sent (grammatically: I had been-sent).

For a woman speaking, it would be:

ja sam bila poslala (feminine forms bila, poslala).

Could I just say Jučer sam već poslao životopis without bio? Does the meaning change?

Yes, you can say:

Jučer sam već poslao životopis.

This is very natural and probably more common in everyday speech than using the pluperfect.

Meaning-wise, in context, it usually still means Yesterday I had already sent the CV – the combination of jučer (yesterday) and već (already) makes the “earlier in the past” idea clear enough.

So:

With bio: more explicit “past before another past”, somewhat more formal/written or emphatic.
Without bio: normal perfect tense, very common in speech; context supplies the “earlier” meaning.

Why is the word order Jučer sam već bio poslao? Can I move sam somewhere else?

The auxiliary sam is a clitic (an unstressed short word) and in Croatian clitics normally stand in second position in the clause.

In Jučer sam već bio poslao životopis:

Jučer = first stressed element of the clause.
sam = clitic goes into second position.
već bio poslao = the rest of the verb phrase.

Some variants are possible, e.g.:

Jučer sam već poslao životopis.
Jučer sam poslao već životopis (possible but less natural).

But you cannot normally move sam later, e.g.:

✗ Jučer već bio poslao sam životopis – wrong/clumsy word order.
✗ Jučer već sam bio poslao životopis – also incorrect, because sam is no longer directly in second position.

The key rule to remember: in a simple clause, sam / si / je / smo / ste / su tend to come immediately after the first stressed word or phrase.

What does ga refer to in ali sam ga morao promijeniti, and why is it ga?

Ga is a clitic object pronoun meaning “him/it” in the accusative singular masculine.

In this sentence, ga refers back to životopis:

životopis is masculine, singular → the right pronoun is ga.
ali sam ga morao promijeniti = but I had to change it.

Word order with clitics:

ali sam ga morao promijeniti – correct and natural.
You normally can’t put it at the end like in English:
✗ ali sam morao promijeniti ga – sounds wrong/foreign.

Why is it prije roka, not prije rok?

Because prije (before) is a preposition that takes the genitive case.

rok (nominative) → roka (genitive).
prije roka literally = before of-deadline → before the deadline.

Other examples with prije:

prije posla – before work
prije ručka – before lunch
prije utakmice – before the match

What’s the difference between poslati and slati? Why is it poslao here and not slao?

Croatian has aspect pairs:

slati – imperfective (ongoing, repeated action) → past: slao sam
poslati – perfective (single, completed action) → past: poslao sam

In this sentence, we talk about one completed act of sending:

bio poslao = had (already) sent (completed result).

Using slao would suggest a process or repeated sending, e.g.:

Jučer sam slao puno životopisa.
Yesterday I was sending / sent a lot of CVs (repeatedly/as a process).

Here we just care about the fact that the CV was already sent, so the perfective poslati → poslao is appropriate.

What’s the difference between promijeniti and mijenjati?

Again, aspect:

mijenjati – imperfective (to be changing, to change repeatedly).
promijeniti – perfective (to change completely / once).

In morao promijeniti, the speaker had to perform one complete change of the CV:

morao sam promijeniti životopis = I had to (completely) change the CV (to a new version).

If you said:

morao sam mijenjati životopis,
it would sound more like I had to be changing the CV (a lot / repeatedly / as an ongoing process).

So promijeniti fits better with the idea of one-off, finished change before the deadline.

Why is it morao promijeniti, not something like morao da promijeni?

In standard Croatian, morati is followed directly by an infinitive:

moram ići – I must go
moraš učiti – you must study
morao sam promijeniti – I had to change

Constructions like morati da + present tense (morao da promijeni) are characteristic of Serbian (and some dialects), but are not standard Croatian.

So:

ali sam ga morao promijeniti prije roka – standard Croatian.
✗ ali sam ga morao da promijenim prije roka – Serbian pattern, not standard in Croatia.

Why is the first clause in pluperfect (sam bio poslao) but the second in perfect (sam morao promijeniti)? Shouldn’t they match?

They don’t have to match, because they refer to two different positions in time:

Jučer sam već bio poslao životopis
– the sending happened earlier, before some later past situation.
ali sam ga morao promijeniti prije roka
– the needing to change (and the change itself) is that later past situation, but still in the past relative to now.

So the timeline is:

First: CV was (already) sent. → pluperfect (bio poslao) marks “earlier past”.
Then: Before the deadline, he realized/decided he had to change it. → perfect (sam morao) is enough.

In practice, Croatians often simplify and use the perfect for both, relying on već and context:

Jučer sam već poslao životopis, ali sam ga morao promijeniti prije roka.
This is very natural and commonly used.

Can I move već to another place, like Jučer već sam bio poslao životopis?

You cannot move već in a way that pushes sam out of second position.

✗ Jučer već sam bio poslao životopis – sounds wrong, because sam is no longer the second element.

Natural options include:

Jučer sam već bio poslao životopis… (given version)
Jučer sam već poslao životopis… (without bio, also natural)

Other positions for već are possible but can sound marked or awkward depending on context. Safest pattern to remember:

[First word/phrase] + sam
- već
  - main verb
    → Jučer sam već poslao / bio poslao životopis.

How would this sentence change if the speaker is female?

Only the past participles change to the feminine forms; sam / morala still show 1st person singular:

Jučer sam već bila poslala životopis, ali sam ga morala promijeniti prije roka.

Changes:

bio poslao (masc.) → bila poslala (fem.)
morao (masc.) → morala (fem.)

Everything else stays the same.