Learn Hardcore Portuguese (Brazil): Hoje à noite estou livre, então prometo que vou ouvir você e não vou ficar muito sério. - Tonight I am free, so I promise that I will listen to you and I will not be too serious.

Hoje à noite = specifically tonight, the night of today.
Esta noite = this night, which can mean tonight but is used less often in Brazil in everyday speech.

In Brazilian Portuguese, hoje à noite is the most natural and common way to say “tonight”.
Esta noite is not wrong, but it can sound a bit more formal, written, or literary depending on context.

Why is it estou livre and not sou livre in this sentence?

Portuguese distinguishes between:

ser = more permanent or defining characteristics
estar = temporary states, situations, or locations

Here, being free tonight is a temporary situation, not a permanent characteristic of the person. So:

Hoje à noite estou livre = Tonight I’m free (temporarily)
Eu sou livre would mean I am free (as a person, not enslaved, independent, etc.) — a more permanent idea.

That’s why estou livre is the natural choice.

Could I say Estarei livre hoje à noite instead of Hoje à noite estou livre?

Yes, you can say Estarei livre hoje à noite, and it is grammatically correct. The difference is nuance and style:

Hoje à noite estou livre: uses the present to talk about a scheduled future; very common in conversation, sounds natural and relaxed.
Estarei livre hoje à noite: uses the simple future; sounds a bit more formal or planned/assured.

In casual spoken Brazilian Portuguese, the version with the present (estou livre) or with ir + infinitive is much more common.

Why is it vou ouvir instead of the future form ouvirei?

Brazilian Portuguese usually prefers the structure:

ir (in present) + infinitive → vou ouvir (I’m going to listen)

instead of the synthetic future:

ouvirei (I will listen)

Both are grammatically correct, but:

Vou ouvir is the everyday, natural spoken form for future actions.
Ouvirei sounds formal, written, or a bit stiff in modern Brazilian Portuguese.

So prometo que vou ouvir você is exactly what people actually say.

In English we say “listen to you”. Why is it ouvir você with no preposition?

The verb patterns are different in Portuguese:

English: listen to someone
Portuguese: ouvir alguém (no preposition)

So you say:

Vou ouvir você = I’m going to listen to you
not vou ouvir a você in standard Brazilian usage.

(You might see ouvir a alguém in very formal or old-fashioned language, but it’s not common in everyday Brazilian speech.)

Could I say vou te ouvir instead of vou ouvir você? Is there any difference?

Yes, you can say vou te ouvir, and it’s very common.

Vou ouvir você – slightly more neutral/explicit; uses the stressed pronoun você.
Vou te ouvir – sounds very natural and conversational; uses the unstressed object pronoun te.

In Brazilian Portuguese:

With você, you normally use você as the object as well: ouvir você.
But many speakers also say te ouvir even when they use você as the subject; this is common in informal speech and varies by region.

Both vou ouvir você and vou te ouvir are acceptable and sound natural in Brazil, especially in casual contexts.

What does então do in this sentence? Could I use por isso or porque instead?

In the sentence:

…estou livre, então prometo que vou ouvir você…

então works as a connector meaning “so” / “therefore” / “in that case”.

Possible alternatives and nuances:

por isso = for that reason / because of that, a bit more explicit and slightly more formal than então:
- …estou livre, por isso prometo que vou ouvir você…
porque = because and usually introduces a reason clause, not a consequence clause. To use porque, you’d normally invert the order:
- Prometo que vou ouvir você porque estou livre.
  (I promise I’ll listen to you because I’m free.)

So então here is a natural, conversational way to connect cause and consequence, similar to English “so”.

Why is it não vou ficar muito sério instead of não vou ser muito sério?

In Portuguese:

ser sério = to be a serious person (character trait)
ficar sério = to become / get serious (change of state or temporary attitude)

The speaker is talking about their mood/attitude tonight, not their permanent personality. So they choose:

não vou ficar muito sério = I’m not going to get too serious / act too serious.

Não vou ser muito sério would sound more like “I’m not going to be a very serious person,” which is less natural in this context.

Does ficar muito sério here mean “be very serious” or “become very serious”?

It can suggest both “get serious” and “stay/act serious”, depending on context.

In this sentence, the idea is roughly:

I promise I’ll listen to you and I won’t (get / be) too serious about it.

So it implies not adopting a very serious attitude, maybe staying relaxed or light-hearted. Ficar often carries the sense of entering or maintaining a state, not a permanent trait.

Is muito sério correct if I mean “too serious”? Should it be sério demais?

Both are possible, but there is a nuance:

muito sério = very serious (strong degree, but neutral)
sério demais = too serious (excessive, more than desirable)

In everyday speech, people often use muito in a somewhat flexible way, and não vou ficar muito sério can be understood as:

I’m not going to be very/too serious (don’t worry).

If you clearly want the idea of “too serious (excessively)”, não vou ficar sério demais is more precise:

…e não vou ficar sério demais.

Is this sentence formal or informal? Does it sound natural in conversation?

The sentence is informal–neutral and sounds very natural in conversation, especially in Brazilian Portuguese:

Use of você (standard informal “you” in Brazil)
Use of vou + infinitive instead of the more formal future form
Overall friendly tone

You could easily say this to a friend, partner, or family member. It’s not slangy, so it wouldn’t be out of place in most everyday contexts.

How would I change the sentence if I were talking to more than one person (you all)?

You mainly need to change você to vocês:

Hoje à noite estou livre, então prometo que vou ouvir vocês e não vou ficar muito sério.

This means:

Tonight I’m free, so I promise I’ll listen to you all and I won’t be too serious.

Everything else (verb forms, etc.) stays the same here, because vou ouvir already matches eu (I), not vocês.

Why is there a comma before então? Is it required?

The comma before então separates two clauses:

Hoje à noite estou livre,
então prometo que vou ouvir você…

In writing, it’s standard and recommended to put a comma before connectors like então, por isso, mas, when they link independent clauses.

In speech, you naturally pause a little there, which matches the comma. So:

Hoje à noite estou livre, então…

is the normal punctuation.

Can I omit eu in (eu) prometo? Why doesn’t the sentence show the subject pronoun?

Yes, omitting eu is normal and correct.

In Portuguese, the verb ending shows the subject, so you don’t always need the pronoun:

(Eu) prometo que vou ouvir você…

Prometo is a 1st person singular form, so it already tells you the subject is eu. Adding eu is only necessary when you want to emphasize “I”:

Eu prometo que vou ouvir você = I promise I’ll listen to you (as opposed to someone else).

In your sentence, leaving out eu keeps it smooth and natural.