Eu prometo ajudar a Ana hoje à noite.

I promise to help Ana tonight.

Breakdown of Eu prometo ajudar a Ana hoje à noite.

• eu: I
• Ana: Ana
• hoje: today
• a noite: the night
• ajudar: to help
• prometer: to promise

Questions & Answers about Eu prometo ajudar a Ana hoje à noite.

Why is there an a before Ana? Isn’t Ana just a proper name?

That a is not the feminine article but the preposition required by the verb ajudar. In European Portuguese, ajudar is normally transitive-indirect, so it takes a + (person). Proper names don’t need an extra article, so you have a Ana (preposition + name), not à Ana (which would be preposition + article).

Can I drop the preposition and say ajudo Ana instead of ajudo a Ana?

In BP you’ll sometimes hear ajudo Ana, but in Portugal the standard is ajudar a + object. So you say ajudo a Ana, prometo ajudar a Ana, etc. Omitting that a in PT-PT will sound non-standard.

Why is there a grave accent on à in hoje à noite?

À is the contraction of the preposition a + the feminine definite article a (because noite is feminine). So:
a (prep.) + a (art.) → à
That’s why you see it in à tarde, à noite.

Why do we say hoje à noite instead of hoje de noite or just hoje noite?

European Portuguese expresses “at night” with à noite. To pin it to today you insert hoje in front: hoje à noite = “this evening/tonight”. You cannot say hoje noite (ungrammatical), and hoje de noite is not used in Portugal (though you may hear de noite alone meaning “by night”).

Could I start the sentence with the time expression? For example, Hoje à noite prometo ajudar a Ana?

Yes. Portuguese allows flexible word order. Moving hoje à noite to the front simply shifts the emphasis to “tonight,” but the meaning stays the same:
Hoje à noite prometo ajudar a Ana.

Do I have to include the subject pronoun Eu? Could I just say Prometo ajudar a Ana hoje à noite?

You can drop Eu because Portuguese is a pro-drop language. The verb ending -o in prometo already tells you the subject is I. Adding Eu is only for emphasis or clarity.

Why is prometo in the present tense and not prometerei (future)?

In colloquial European Portuguese the simple present often expresses a near-future promise or intention. While prometerei ajudar a Ana is grammatically correct, it sounds more formal or literary. Prometo ajudar a Ana hoje à noite is what you’d use in everyday speech.

Why isn’t there a que after prometo (like “I promise that…”)?

Some Portuguese verbs (including prometer) can take an infinitive directly as a complement, so no que is needed:
prometo + ajudar
If you really want que, you’d say prometo que vou ajudar a Ana hoje à noite, but the infinitive construction is more natural here.

How would I replace a Ana with a pronoun to say, “I promise to help her tonight”?

You have two main options in PT-PT:
1) Enclitic direct-object pronoun after the infinitive:
prometo ajudá-la hoje à noite
2) Indirect-object pronoun before the infinitive (more formal):
prometo lhe ajudar hoje à noite
Both mean “I promise to help her tonight,” though option 1 is the most common in speech.