Learn Hardcore Croatian: Kad se osjećaš drugačije, reci mi kako ti je. - When you feel different, tell me how you are.

Kad and kada are basically the same word. Kada is just the full, slightly more formal or emphatic form. In everyday speech people mostly say kad.

You can use either here:

Kad se osjećaš drugačije, reci mi kako ti je.
Kada se osjećaš drugačije, reci mi kako ti je.

Both are correct and mean the same thing.

Why is se in the middle of kad se osjećaš? What is se doing?

Se is a reflexive pronoun that belongs to the verb osjećati se (to feel as in to feel (a certain way)).

In Croatian, short words like se, mi, ti, je, etc. (called clitics) tend to go very early in the sentence or clause – usually in second position.

So instead of:

✗ Kad osjećaš se… (sounds wrong)

Croatian prefers:

✓ Kad se osjećaš…

Here:

osjećaš = you feel
se = makes it you feel (yourself), i.e. you feel (in yourself), the normal way to say you feel about your emotional/physical state.

What is the infinitive of osjećaš, and does osjećati always use se?

The infinitive is osjećati.

There are two main patterns:

osjećati se = to feel (emotionally or physically, like a state)
- Osjećam se dobro. – I feel good.
- Osjećaš se umorno. – You feel tired.
osjećati + object = to feel (something with your senses or emotions directed at something)
- Osjećam hladnoću. – I feel the cold.
- Osjećaš ljubav. – You feel love.

In your sentence, osjećaš se is used because it’s about how you yourself feel (your condition), not what you feel as an object.

Why is drugačije used here and not drugačiji or drugačka or something like that?

Drugačije in this sentence is an adverb, meaning differently.

Croatian often expresses how you do something with adverbs ending in -e:

dobro – well
loše – badly
drugačije – differently

So:

osjećaš se drugačije = you feel differently (how you feel)

If you used an adjective, you’d be describing a noun, for example:

Drugačiji čovjek. – A different man. (adjective drugačiji describing čovjek)
Osjećaš se drugačijim čovjekom. – You feel like a different man. (here drugačijim agrees with čovjekom)

In your sentence there’s no noun; it’s just you feel differently, so drugačije (adverb) is correct.

Why is it reci mi and not kaži mi or something else? What exactly is reci?

Reci is the imperative (command) form of the verb reći (to say, to tell). It means say (to one person) or tell (one person).

You can also hear kaži from kazati, which is very common in speech:

Reci mi kako ti je.
Kaži mi kako ti je.

Both mean Tell me how you feel / how it is for you.

Minor nuance: reći is a bit more standard/literary, kazati a bit more colloquial in some regions, but in most everyday contexts they are interchangeable here.

What does mi mean in reci mi? Is it me or my?

Here mi means to me, not my.

It’s the dative form of ja (I), used for indirect objects:

Reci mi. – Tell me. (tell to me)
Daj mi knjigu. – Give me the book.
Piši mi. – Write to me.

So:

reci = say / tell
mi = to me

Together: Reci mi… = Tell me…

Why is there a comma before reci mi? Is it required?

Yes, the comma is standard here because the sentence has two clauses:

Kad se osjećaš drugačije – when you feel different(ly) (a dependent clause)
reci mi kako ti je – tell me how you are (the main clause)

In Croatian, when a dependent clause like kad se osjećaš drugačije comes before the main clause, you normally put a comma between them:

Kad dođeš, nazovi me. – When you come, call me.
Ako možeš, pomozi mi. – If you can, help me.

So the comma in Kad se osjećaš drugačije, reci mi kako ti je. is expected and correct.

What does kako ti je literally mean, word by word?

Literally:

kako = how
ti = to you / for you (dative of ti = you, singular informal)
je = is (3rd person singular of biti = to be)

So word for word:
kako ti je = how is it to you / how is it for you

In natural English this becomes:

How are you (feeling)?
How is it for you?

In context with osjećaš se, it clearly means how you feel.

Why is the verb je at the end of kako ti je? Could you say kako je ti?

Je is another clitic (like se, mi, etc.), and Croatian has strong rules for where clitics go. In short questions or clauses starting with a question word like kako, the typical pattern is:

Question word + clitic(s) + rest

So:

Kako ti je? – How are you?
Gdje si bio? – Where were you? (si = you are/were)
Kada si došao? – When did you come?

Kako je ti is wrong; the clitic ti must come early, and je follows it. The correct order here is precisely kako ti je.

Why is it kako ti je and not kako se osjećaš? Do they mean the same thing?

They are very close in meaning, but not identical in nuance:

Kako ti je?
Literally How is it for you?
Very common, general: can mean How are you (doing)?, How are you feeling?, or even How is your situation?
Kako se osjećaš?
Literally How do you feel?
Focuses more explicitly on your internal feeling (physical/emotional state).

In your sentence:

Kad se osjećaš drugačije, reci mi kako ti je.

The first part already uses osjećaš se (feel differently), so the second part can just say kako ti je without repeating osjećaš. It sounds natural and not repetitive.

Is ti in kako ti je the subject you?

Grammatically, no. In kako ti je, ti is dative: to you / for you. The subject is understood/implicit with the verb je (which comes from biti = to be).

However, in English we conceptually translate kako ti je? as How are you?, where you is the subject. Croatian uses a different structure (how is it to you), but the meaning is effectively the same: asking about you and your state.

So:

form: dative (to you)
function in meaning: asking about your condition.

Could I say Kad osjećaš se drugačije instead of Kad se osjećaš drugačije?

No, that sounds wrong to native speakers.

Because se is a clitic, it prefers to stand early in the clause, usually after the first stressed word (here kad). So:

✓ Kad se osjećaš drugačije… (natural)
✗ Kad osjećaš se drugačije… (unnatural)

This rule applies generally:

Kad se vratiš, javi mi se. – When you come back, let me know.
Ako se bojiš, reci mi. – If you’re afraid, tell me.

Clitics like se, mi, ti, ga, je, sam/si/je/smo/ste/su usually avoid the very beginning of the sentence but want to be as early as possible after the first full word.