Impersonal trebati

In the last lesson you met sviđa mi se: the thing you like is the grammatical subject, and you — the person doing the liking — stand in the dative. Serbian says I need in exactly the same way. The thing you need is the subject, the verb trebati agrees with it, and the person who needs it is in the dative: Treba mi lampa — literally "a lamp is-needed to-me".

Treba mi + the thing you need

Because the thing needed is the subject, the verb changes with it, not with you. One thing: treba. Several things: trebaju. In the past the l-participle takes the gender and number of the thing, just as it did with sviđati se.

The needer takes the dative clitics you already know — mi, ti, mu, joj, nam, vam, im — sitting in second position, or a full dative noun: Marku treba nova stolica (Marko needs a new chair). For emphasis or contrast use the stressed pronoun: Meni treba tiganj, a tebi šerpa.

• Negation: Ne treba mi ništa. (I don't need anything.) — ne goes before the verb as usual.
• Question: Šta ti treba? (What do you need?) / Treba li vam kesa? (Do you need a bag?)
• Nothing at all: Ne trebaju mi nove čaše. — plural thing, plural verb, still negated with ne.

Treba da + verb: what someone ought to do

The same verb does a second job. Put treba in front of a da-clause and it means should / ought to / it is necessary that. Here treba is fixed — it is always the bare 3rd person singular, whoever is meant to act. The person shows only in the verb after da:

In the past treba becomes the neuter trebalo je: Trebalo je da kupimo veći ormar (we should have bought a bigger wardrobe). Negated, ne treba da means there is no need to / shouldn't: Ne treba da trošiš toliko novca (you shouldn't spend that much money).

Do not confuse treba da with morati. Moram da platim is I must pay — no choice. Treba da platim is softer: I ought to, it would be right to. If you would say "should" in English, treba da is the word; if you would say "must" or "have to", it is morati.

In everyday speech you will hear trebati conjugated like an ordinary verb — Trebam da kupim lampu, Trebaš da odeš, even Trebam novu lampu with a plain accusative object. Understand it when you hear it, but write and say the standard form: treba da kupim, treba mi lampa.

Telling the two apart

What follows treba decides the meaning. A noun after it (with a dative person) is someone needs something; da + a verb after it is someone should do something. Treba mi metla — I need a broom. Treba da kupim metlu — I should buy a broom.