Learn Hardcore Croatian: Moj kolega i ja učimo u istoj učionici. - My male colleague and I study in the same classroom.

The subject is moj kolega i ja (my colleague and I), which is we in English.
In Croatian, the verb must agree with the subject in person and number:

učim – I study (1st person singular)
učiš – you study (singular)
uči – he/she/it studies (3rd person singular)
učimo – we study (1st person plural) ✅
učite – you study (plural/formal)
uče – they study (3rd person plural)

Because the subject includes ja (I), it becomes we, so the correct form is učimo.

Why is it moj kolega i ja and not ja i moj kolega?

Both moj kolega i ja and ja i moj kolega are grammatically correct.

In careful or formal Croatian (similar to English), it is more polite to put yourself last:
- Moj kolega i ja učimo… – preferred in writing and formal speech.
In casual speech, you will also hear:
- Ja i moj kolega učimo…

So the textbook-style, neutral form is Moj kolega i ja…, but you can understand and sometimes use Ja i moj kolega… as well.

Why is it ja and not mene in moj kolega i ja?

Ja is the nominative form (used for the subject of the sentence).
Mene is not nominative; it’s used for objects (accusative/genitive) and after prepositions.

Since moj kolega i ja is the subject (the ones doing the studying), you must use ja:

✅ Moj kolega i ja učimo… – My colleague and I study…
❌ Moj kolega i mene učimo… – ungrammatical

What case is moj kolega in, and why?

Moj kolega is in the nominative singular.

The nominative is the case used for the subject of the sentence – the person/thing doing the action.
Here, the subject is moj kolega i ja, so kolega must be in the nominative.

You could think of it as the “dictionary form” of the noun, the one you normally look up.

Why is kolega (colleague) masculine if it ends in -a, which usually marks feminine nouns?

Kolega is one of a small group of masculine nouns ending in -a. These refer to males but look like feminine words:

kolega – (male) colleague
vojvoda – duke
gazda – (male) boss, landlord

Important points:

The meaning is masculine (a male person).
The agreement is masculine:
- moj kolega (my colleague – masc.)
- dragi kolega (dear colleague – masc.)
But the case endings mostly follow the feminine pattern (like učionica → učionici).

The female form of kolega is kolegica (colleague, female).

What is the difference between učiti and studirati?

Both can translate as to study, but they are used differently:

učiti
- to learn, to study (for an exam, homework, material)
- common in school context, for specific content
- Moj kolega i ja učimo u istoj učionici. – We are (learning/studying) in the same classroom.
studirati
- to study a field of study at university
- used with the name of a subject or faculty
- Studiram biologiju. – I study biology.
- Ona studira na fakultetu. – She is at university (studies there).

In your sentence, učiti is correct because you mean actually sitting in a classroom and doing schoolwork/learning.

Why is it u istoj učionici and not u ista učionica?

Two reasons: case and agreement.

Preposition u with a static location uses the locative case:
- u učionici – in the classroom (locative)
- u učionicu – into the classroom (accusative, motion towards)
Here, you are inside the classroom, not moving into it, so you use the locative:
učionica → učionici.
The adjective isti (same) must agree with učionica in gender, number, and case:
- učionica – feminine, singular, locative
- so isti becomes istoj (feminine, singular, locative)

So you get:

u istoj učionici = in the same classroom ✅
u ista učionica – wrong case and no agreement ❌

What exactly is the form istoj in u istoj učionici?

Iistoj is the feminine singular locative form of the adjective isti (same).

Basic nominative forms of isti are:

isti – masculine singular
ista – feminine singular
isto – neuter singular

In u istoj učionici:

učionici is feminine singular, locative.
The adjective isti must match that, so it becomes istoj.

So istoj literally means “same” in the form required by u učionici (in the classroom).

Why is učionica changed to učionici?

This is again the locative case.

The base noun is učionica (classroom, feminine). For many feminine nouns ending in -a, the locative singular (and dative singular) ending is -i:

učionica (Nominative) → učionici (Locative)
škola (school) → školi (in/at school)
kuća (house) → kući (at home / at the house)

Because of u (in) with a location, učionica must be in the locative: učionici.

What is the rule for the preposition u? When do I use locative, and when accusative?

U can take locative or accusative, depending on the meaning:

Locative – when something/someone is in a place (static position):
- u učionici – in the classroom
- u gradu – in the city
- u parku – in the park
Your sentence: učimo u istoj učionici – you are already in the classroom.
Accusative – when there is motion into a place (direction):
- idem u učionicu – I’m going into the classroom
- trči u park – he runs into the park
- vozim u grad – I’m driving to the city

So: Where? → locative, Where to? → accusative with u.

Why aren’t there words like the or a in the Croatian sentence?

Croatian has no articles like English a/an or the.

Instead, definiteness and specificity are understood from:

context,
word order,
pronouns and adjectives (like taj – that, ovaj – this, isti – same, etc.).

So:

učionica can mean a classroom or the classroom, depending on context.
Here, u istoj učionici is naturally understood as in the same classroom from istoj (same) and the context of two people sharing it.

Can I drop moj or ja and still be correct?

You can sometimes drop words, but you must keep the grammar consistent.

Dropping moj:
- ✅ Kolega i ja učimo u istoj učionici. – My colleague and I study in the same classroom.
  Here kolega is still understood as my colleague from context (if already known).
Dropping ja:
- You should not usually drop ja and keep the plural verb, because then it looks like the subject is only kolega (singular) but the verb is učimo (we).
- ✅ Moj kolega i ja učimo… – correct (subject is plural: he + I)
- ❌ Moj kolega učimo… – wrong (singular noun with plural verb)

In Croatian you often drop subject pronouns when the verb form alone is enough (e.g. Učimo. – We are studying.), but once you name one part of the subject (moj kolega), it’s better to keep ja as well.

What is the difference between kolega and prijatelj, and between učionica and razred?

Two separate pairs:

kolega vs prijatelj
- kolega – colleague, someone you work or study with (same school, job, profession).
- prijatelj – friend (personal friend, closer relationship).
So moj kolega means my colleague, not necessarily my friend.
učionica vs razred
- učionica – the classroom (the physical room).
- razred – can mean:
  - a class/grade (group of students),
  - or a year in school (e.g. 7th grade).
Your sentence is about the room, so učionica (→ učionici in locative) is the right choice.