Learn Hardcore Romanian: Trebuie să vorbesc cu Ana diseară.

Literally, trebuie means “it is necessary,” and să is the marker that introduces a subordinate verb in the subjunctive.
Idiomatic translation: Trebuie să vorbesc… = “I have to speak…” or “I must speak….”

Why does vorbesc follow să, and what mood is it?

After să, Romanian uses the present subjunctive. The form of the subjunctive for eu (“I”) is identical to the present indicative, so vorbesc looks the same in both moods but here it’s subjunctive.

Why can’t we omit să and say Trebuie vorbesc cu Ana diseară?

In Romanian, most verbs of necessity, desire, doubt, etc., require să before another verb to form the subjunctive. Omitting să would be ungrammatical.

What does the preposition cu express in vorbesc cu Ana?

cu means “with” here. To say “to speak with someone,” you use a vorbi cu cineva. You cannot use la or pe in this context—cu marks the person you’re conversing with.

What does diseară mean, and is astă-seară the same thing?

diseară = “tonight” / “this evening.”
astă-seară (often written astă seară) also means “this evening/tonight.”
Nuances: diseară is one word and slightly more neutral; astă-seară is a bit more explicit (“this particular evening”), but in everyday speech they’re interchangeable.

Can the word order change? For example, could I say Diseară trebuie să vorbesc cu Ana?

Yes. Romanian has relatively flexible word order for emphasis:

Trebuie să vorbesc cu Ana diseară. (neutral)
Diseară trebuie să vorbesc cu Ana. (emphasizes when)
Trebuie diseară să vorbesc cu Ana. (also possible, less common)

Why is there no article before Ana? Could we say cu o Ana?

Proper names in Romanian don’t normally take a definite or indefinite article. You only use an indefinite article (o) with a common noun, e.g. o Ana would mean “an Ana” – one of several people named Ana (very unusual unless you’re in a classroom full of Anas!).

What are other ways to express obligation instead of Trebuie să?

Several alternatives convey a similar idea:
• Am nevoie să vorbesc cu Ana diseară. (“I need to speak with Ana tonight.”)
• Este necesar să vorbesc cu Ana diseară. (“It’s necessary that I speak with Ana tonight.”)
• Am de vorbit cu Ana diseară. (more colloquial: “I’ve got to talk with Ana tonight.”)
Each has a slightly different tone, but all express a requirement or need.