Learn Hardcore Croatian: Moja sestra ima dugu kosu, a ja imam kratku kosu. - My sister has long hair, and I have short hair.

ima = he/she/it has or (formal) you have
- 3rd person singular (and also 2nd person formal):
  - Moja sestra ima dugu kosu. – My sister has long hair.
imam = I have
- 1st person singular:
  - Ja imam kratku kosu. – I have short hair.

So the form of imati changes depending on who is doing the having (the subject).

Why is it moja sestra and not moj sestra?

In Croatian, possessive adjectives (my, your, his…) agree in gender, number, and case with the noun they describe.

sestra (sister) is feminine singular.
The word for my must also be feminine singular nominative → moja.

So:

moja sestra – my sister (feminine)
moj brat – my brother (masculine)
moje dijete – my child (neuter)

Moj sestra is wrong because moj is masculine, but sestra is feminine.

Why is it dugu kosu instead of duga kosa?

This is about case.

duga kosa – long hair in the nominative case (subject form)
dugu kosu – long hair in the accusative case (direct object form)

In the sentence:

Moja sestra ima dugu kosu.

The verb ima (has) takes a direct object (what she has).
kosa (hair) is that object, so it has to be in the accusative: kosu.

The adjective duga must agree with kosa/kosu in gender, number, and case:

nominative: duga kosa (subject)
accusative: dugu kosu (object)

So ima dugu kosu is the grammatically correct form after ima.

Why is kosa changed to kosu here? What case is that and when is it used?

kosa (hair) is feminine singular nominative (dictionary form).
In the sentence, it becomes kosu, which is feminine singular accusative.

The accusative case is used mainly for:

direct objects of verbs
- Moja sestra ima dugu kosu. – What does she have? → kosa → accusative kosu
some directions with movement (not relevant here)

So: because hair is the thing possessed (the direct object of ima), it must be in the accusative: kosu.

What does a mean here, and how is it different from i?

In this sentence:

Moja sestra ima dugu kosu, a ja imam kratku kosu.

the a is a conjunction that roughly means:

and, but, or while, showing contrast.

Typical differences:

i = simple and, just adding information
- Moja sestra ima dugu kosu i plave oči. – My sister has long hair and blue eyes.
a = and/but in a contrasting sense
- Moja sestra ima dugu kosu, a ja imam kratku kosu. – My sister has long hair, whereas I have short hair.

So a highlights the difference between your sister’s hair and your hair.

Can I omit ja in a ja imam kratku kosu?

Yes.

Croatian often drops subject pronouns because the verb ending already shows the subject. So you can say:

Moja sestra ima dugu kosu, a imam kratku kosu.

This is grammatically correct and natural.
However, including ja:

a ja imam kratku kosu

adds a bit more emphasis on “I” (contrast: she vs I), which fits the contrast expressed by a.

Why do we repeat kosu in the second part? Can we just say a ja imam kratku?

In full, we have:

Moja sestra ima dugu kosu, a ja imam kratku kosu.

You can omit kosu in the second part because it’s understood from context:

Moja sestra ima dugu kosu, a ja imam kratku.

This is natural and common in speech and writing when the meaning is clear.
However:

the full version with kosu is completely correct and a bit clearer, especially for learners.
omitting kosu makes the sentence slightly more compact and fluent in everyday speech.

Why do dugu and kratku end in -u?

Because these adjectives are:

feminine
singular
accusative case

They have to agree with kosu (feminine singular accusative).

Patterns for a typical feminine adjective like duga (long):

nominative: duga kosa – long hair (as subject)
accusative: dugu kosu – long hair (as object)

Same for kratka (short):

nominative: kratka kosa
accusative: kratku kosu

So the -u ending on dugu/kratku matches the accusative -u on kosu.

Do the adjectives agree with the person (sister / I) or with kosa/kosu?

They agree with kosa/kosu, not with the person.

kosa/kosu is feminine singular
therefore the adjectives (duga/dugu, kratka/kratku) are also feminine singular

Example:

Moj brat ima dugu kosu. – My brother has long hair.
- brat = masculine
- kosa/kosu = feminine
- adjective agrees with kosa/kosu, not with brat → dugu kosu.

So in your sentence, dugu and kratku match kosu (hair), not sestra or ja.

Can I change the word order, like Moja sestra dugu kosu ima?

Croatian word order is fairly flexible, but not all orders sound natural.

Standard and most natural:

Moja sestra ima dugu kosu.

Other possible, but more marked or stylistic, orders:

Moja sestra dugu kosu ima. – possible, but sounds poetic, emphatic, or unusual in everyday speech.
Dugu kosu ima moja sestra. – also possible, stressing dugu kosu or moja sestra.

For a learner, it’s best to stick to:

Subject – verb – object: Moja sestra ima dugu kosu.
A ja imam kratku kosu.

Is there a shorter way to say has long hair / has short hair in Croatian?

The most common and neutral way is exactly what you have:

ima dugu kosu – has long hair
ima kratku kosu – has short hair

There are colloquial or descriptive alternatives but they are less neutral, for example:

dugokosa – long-haired (feminine adjective)
- Moja sestra je dugokosa. – My sister is long‑haired.
kratkokosa – short‑haired (feminine)
- Ja sam kratkokosa. – I am short‑haired.

These are less common in everyday speech than simply ima dugu/kratku kosu, which is the safest and most natural pattern to learn.

Why is there a comma before a?

In Croatian punctuation, a comma is normally used before the conjunction a when it joins two independent clauses:

Moja sestra ima dugu kosu, a ja imam kratku kosu.

Each part could be a full sentence:

Moja sestra ima dugu kosu.
Ja imam kratku kosu.

Because you are connecting two full sentences with a, you put a comma before a, similar to My sister has long hair, and I have short hair in English.