Bare dative of direction

At the end of the day you say one of the most useful sentences in Serbian: Idem kući. — "I'm going home." Notice what is not there. No preposition. English needs a little word before most destinations ("to the office", "to the station"), and Serbian usually needs one too — but not here. kući on its own already means "home, homewards".

The form is the dative singular of kuća (house), which you already know how to make. What is special is that this one dative has frozen solid: it stands alone as an adverb of direction, it never changes, and it never takes a preposition.

Three ways English says "home"

English uses the same word "home" for the place you are heading to and the place you already are. Serbian keeps them apart, and adds a third phrase for the building itself.

Idem kući means you are heading home for the evening — back to your own life, wherever that is. Idem u kuću da uzmem ključeve means you are stepping indoors, out of the garden or off the terrace. And Ceo dan sam kod kuće says where you are, not where you are going.

Before you translate "home", ask one question: goal or place? A goal after a verb of motion is kući. A place is kod kuće. Save u kuću and u kući for when you genuinely mean the building. Never write u kući for "going home" — that says you are sitting inside it.

The verbs it lives with

kući attaches to any verb of movement, in any tense. The verb does all the work of saying which direction — arriving, leaving, setting off, coming back — and kući just names the destination.

• ići — Idem kući, vidimo se sutra. I'm going home, see you tomorrow.
• doći — Dođi kući ranije. Come home earlier.
• stići — Stigao sam kući u osam. I got home at eight.
• otići — Otišla je kući taksijem. She went home by taxi.
• krenuti — Krenuli smo kući posle ponoći. We set off home after midnight.
• vratiti se — Vratio sam se kući kasno. I came back home late.

vratiti se keeps its se, and the clitics queue up in second position as always: Vratio sam se kući, Vraćam se kući, Vratiću se kući. Put kući at the end and the rest falls into place.

One more thing worth knowing: kući is not the only frozen adverbial of its kind, but it is by far the commonest, and it is the one you will hear twenty times a day in Belgrade. Learn it as a word, not as a case ending.