Learn Hardcore Croatian: Kad se osjećaš tužno, nazovi me.

osjećati on its own = to feel (sense, perceive) something
- Osjećam vjetar. – I feel the wind.
osjećati se = to feel (a certain way, emotionally/physically)
- Osjećam se tužno. – I feel sad.

So in this sentence, se is needed:

✅ Kad se osjećaš tužno, nazovi me.
(When you feel sad, call me.)

Without se, it sounds incomplete or wrong in standard Croatian here:

❌ Kad osjećaš tužno, nazovi me. – not correct in this meaning.

Can I say osjećaš se tužno instead of se osjećaš tužno?

Yes, both word orders are possible:

Kad se osjećaš tužno, nazovi me.
Kad osjećaš se tužno, nazovi me.

However, in everyday speech the version with se immediately after kad (or after the subject) is more common and sounds smoother:

Kad se osjećaš tužno… – most natural
Kad osjećaš se tužno… – grammatically OK, but less usual

Croatian clitics (short words like se, me, te, ga, je) like to appear very early in the clause (typically in the “second position”). So Kad se osjećaš… fits the usual pattern better.

Why is it tužno and not tužan or tužna?

tužan, tužna, tužno are adjective forms: sad (masc., fem., neut.)
tužno can also function as an adverb: sadly / in a sad way

In osjećati se + adverb, Croatian often uses the adverb form:

Osjećam se tužno. – I feel sad. (literally “I feel sadly.”)

You can also use the adjective with biti (to be):

Ja sam tužan. (masc.) / Ja sam tužna. (fem.) – I am sad.

So:

Kad se osjećaš tužno… – focuses on the inner feeling, with the adverb.
Kad si tužan / tužna… – uses the adjective and the verb to be.

Both ways are natural; this sentence just uses the adverbial pattern.

Could I say Kad si tužan, nazovi me instead? Is there a difference?

Yes, that is perfectly correct and very natural:

Kad si tužan, nazovi me. (to a male)
Kad si tužna, nazovi me. (to a female)

Difference in nuance:

Kad se osjećaš tužno… – literally “when you feel sadly”; emphasizes the feeling process.
Kad si tužan/tužna… – “when you are sad”; describes your state more directly.

In practice, both are widely used; the meaning is almost the same in everyday speech.

Is osjećaš an informal “you”? How would I say this formally (polite “you”)?

Yes. osjećaš is 2nd person singular – familiar “you” (talking to one person you know well). The polite form in Croatian uses 2nd person plural:

Informal (to one person):
Kad se osjećaš tužno, nazovi me.
Formal / polite (to one person, or to several people):
Kad se osjećate tužno, nazovite me.

Changes:

osjećaš → osjećate
nazovi → nazovite (plural imperative)

The rest of the sentence stays the same.

What is the difference between nazovi me and zovi me?

Both come from the verb zvati / nazvati (to call), but they differ in aspect:

zovi me – from zvati (imperfective)
- can imply repeated or ongoing calling
- e.g. Zovi me svaku večer. – Call me every evening.
nazovi me – from nazvati (perfective)
- refers to one complete act of calling
- e.g. Kad se osjećaš tužno, nazovi me. – When you feel sad, (make a call to) me.

In your sentence, nazovi me is ideal because it sounds like “Give me a ring (once) when that happens.”

Can I change the word order and say Nazovi me kad se osjećaš tužno?

Yes, absolutely. Both are correct:

Kad se osjećaš tužno, nazovi me.
Nazovi me kad se osjećaš tužno.

The meaning is the same.

The difference is just in emphasis and flow:

Starting with Kad… highlights the condition/time.
Starting with Nazovi me… puts more focus on the request/command.

Both sound natural in spoken and written Croatian.

Why is the comma used here? Is it always needed with kad?

In Kad se osjećaš tužno, nazovi me. there are two clauses:

Kad se osjećaš tužno – subordinate clause (time condition: when you feel sad)
nazovi me – main clause (command: call me)

Croatian normally uses a comma to separate a subordinate clause from the main clause:

Subordinate first:
Kad se osjećaš tužno, nazovi me. – comma is standard.
Main clause first:
Nazovi me kad se osjećaš tužno. – usually no comma.

So:

Kad … , [main clause]. → comma
[Main clause] kad … → often no comma in modern usage.

Can kad here also mean “if”, like “If you feel sad, call me”?

Yes, in many contexts kad (when) and ako (if) can overlap in meaning.

Here:

Kad se osjećaš tužno, nazovi me.
can be understood both as:
- When you feel sad, call me. (whenever that happens)
- If you feel sad, call me. (on the condition that you do)

If you want to emphasize condition more clearly, you could use ako:

Ako se osjećaš tužno, nazovi me. – clearly “If you feel sad, call me.”

But the original with kad is very natural and commonly used in this “if/whenever” sense.

Why is the present tense used in both parts? Could I use the future tense instead?

Croatian often uses the present tense in time/conditional clauses with kad to talk about the future, just like English:

Kad se osjećaš tužno, nazovi me.
= When you feel sad (in the future), call me.

Both verbs are in present tense, but the whole sentence refers to future situations.

You could use future in the main clause:

Kad se budeš osjećao tužno, nazvat ćeš me.
(When you feel sad, you will call me.)

This is grammatically correct but sounds more formal and less like a simple friendly instruction. For a natural, everyday request, the imperative + present in the kad-clause is best:

Kad se osjećaš tužno, nazovi me.