Kad nekoga zoveš, koristiš vokativ: "Luka, dođi ovamo!"

Kad means when. In this sentence, it has a general meaning: whenever / when you call someone.

Kad and kada mean the same thing. The difference is mostly style:

• kad = very common in everyday speech
• kada = a bit fuller or more formal

So Kad nekoga zoveš... and Kada nekoga zoveš... both work.

Nekoga is the accusative form of netko, meaning someone.

The verb zvati takes a direct object, so:

• zoveš nekoga = you call someone

In casual speech, you may also hear nekog, but nekoga is the full standard form.

It can mean either one. Croatian zvati is broader than English call.

Here, because the sentence talks about the vocative and gives the example Luka, dođi ovamo!, it means calling out to someone / addressing someone by name.

For phone calls, Croatian also often uses:

• nazvati nekoga = to call someone
• telefonirati nekome = to phone someone

This is a generic you, just like in English grammar explanations.

So:

• Kad nekoga zoveš, koristiš vokativ
  means
• When you call someone, you use the vocative

It does not refer to one specific person. Croatian often uses 2nd person singular this way.

The vocative (vokativ) is the case used when you speak directly to someone or something.

Examples:

• Ana, dođi!
• Ivane, slušaj!
• Prijatelju, pomozi mi!

So the point of the sentence is: when you address someone by name, Croatian uses the vocative.

Often it does, but not always.

Some nouns and names have a vocative form that looks different from the nominative:

• Ivan → Ivane
• prijatelj → prijatelju

But some names are very commonly used with a vocative that looks the same as the nominative:

• Luka → Luka
• Marko → Marko
• Marija → Marija

So Luka is still functioning as a vocative here, even though the form does not visibly change.

No, not all of them.

A useful way to think about it is:

1. Some names change in the vocative:
   • Ivan → Ivane
   • Petar → Petre
2. Some names stay the same:
   • Luka → Luka
   • Marko → Marko
   • Marija → Marija

Also, in modern everyday speech, some speakers use special vocative forms less often than older textbooks might suggest, especially with personal names.

Because Luka is being used in direct address.

In Croatian, as in English, when you say someone's name to address them directly, you normally separate it with a comma:

• Luka, dođi ovamo!

The comma shows that you are talking to Luka.

Dođi is the 2nd person singular imperative of doći, meaning to come.

So:

• dođi = come!

That is why Luka, dođi ovamo! means Luka, come here!

A useful related form:

• dođite = come! for more than one person, or for polite you

Because dođi expresses movement toward the speaker.

• ovamo = to here / over here
• ovdje = here as a location

So:

• Dođi ovamo. = Come here.
• Knjiga je ovdje. = The book is here.

With a verb of movement like doći, ovamo is very natural.

Yes. Both are natural.

Croatian word order is fairly flexible, so:

• Kad nekoga zoveš...
• Kad zoveš nekoga...

both mean When you call someone...

The difference is mostly about style or emphasis, not basic meaning.

Because Croatian usually leaves out the subject pronoun when the verb ending already shows who the subject is.

Here:

• zoveš already means you call
• koristiš already means you use

So ti is unnecessary unless you want special emphasis:

• Ti koristiš vokativ, a ja ne. = You use the vocative, and I don't.