Learn Hardcore Portuguese (Portugal): A carruagem estava cheia, mas esse assento ficou livre de repente. - The carriage was full, but that seat suddenly became free.

The imperfect sets background or ongoing states in the past. A carruagem estava cheia paints the scene as “the carriage was (in general) full.” The preterite would make it a bounded, completed state: A carruagem esteve cheia = “it was full (for a certain period).” In your sentence, the “full carriage” is background for the sudden event that follows, so the imperfect is the natural choice.

Why ficou livre and not estava livre?

Ficar often means “to become/turn” (a change of state). With de repente, ficou livre highlights the moment a seat changed from occupied to available. Estava livre would simply describe the state (it was free), not the sudden change.

Could I use tornou-se or passou a estar instead of ficou?

Yes, but they change the tone:

Tornou-se livre sounds more formal or literary.
Passou a estar livre suggests a transition but is wordier and slightly less abrupt than ficou livre. For everyday speech, ficou livre is the idiomatic choice.

What’s the nuance between livre, vazio, disponível, and vago for seats?

Livre = free/available to use (natural for seats).
Vazio = empty; no one is sitting there, but it might still be reserved.
Disponível = available (more formal/neutral).
Vago = vacant; common in set phrases like lugar vago (vacant seat), also used for positions/jobs.

Assento vs lugar vs cadeira: which should I use?

Assento = the physical seat.
Lugar = seat as a place/slot, often tied to a booking (e.g., lugar marcado = reserved seat).
Cadeira = chair (a standalone piece of furniture). On trains in Portugal, both assento and lugar are common; here assento is perfect.

What exactly does carruagem mean in Portugal? How does it compare to comboio and vagão?

Comboio = train.
Carruagem = a coach/car of the train (the carriage).
Vagão is Brazilian; it’s understood but not the usual word in Portugal. Use carruagem in European Portuguese.

Why esse and not este or aquele? How do I choose demonstratives in European Portuguese?

In European Portuguese:

Este = near the speaker or about to be introduced.
Esse = near the listener or just mentioned in discourse.
Aquele = far from both or outside the immediate context. Here, esse assento implies “that seat (you can see/you’re near/you know the one we mean).” If it were far across the carriage, aquele assento could fit.

Could I say aquele assento in this sentence?

Yes, if the seat is distant from both speaker and listener or being pointed out across the carriage. Esse suggests it’s nearer to the listener or already topical; aquele pushes it further away.

Is the comma before mas required?

Yes. In Portuguese, adversative conjunctions like mas (“but”) normally take a comma before them: …, mas …

Can de repente move around in the sentence?

Yes. All of these are fine, with slightly different rhythm/emphasis:

De repente, esse assento ficou livre.
Esse assento, de repente, ficou livre.
Esse assento ficou livre de repente. (your version; very natural)

Any colloquial ways to say the carriage was really full?

Yes:

A carruagem estava à pinha.
A carruagem estava apinhada.
A carruagem estava a abarrotar. All sound very natural in Portugal.

Pronunciation tips for European Portuguese in this sentence?

Approximate cues:

carruagem: the rr is a guttural sound; final -gem = “zheng.”
cheia: initial ch = “sh,” diphthong like “shay-ah.”
mas esse: the final s in mas links as a “z” before a vowel, so it sounds like “mahz ES-se.”
de often reduces to a very quick, weak vowel (like “d(uh)”).
livre: final e is not “ee”; it’s a short, relaxed vowel (“LEEV-r(uh)”). These are rough guides; local accents vary.

Why is cheia feminine, while livre doesn’t change here?

Carruagem is feminine, so the adjective agrees: carruagem cheia.
Assento is masculine singular, and livre (singular) is the same for masculine and feminine (plural: livres). So assento livre is correct.

Any spelling pitfalls I should watch for?

Assento (seat) has double s. Don’t confuse it with acento (accent mark).
Carruagem has rr (guttural sound) and ends with -gem (pronounced “zheng”).
De repente is two words.

Are there good synonyms for ficou livre?

Yes, depending on tone:

ficou vago
ficou desocupado
passou a estar livre Avoid libertou-se here (that’s “freed itself”). And liberou is Brazilian usage; in Portugal you’d say ficou livre or desocupou-se (e.g., O lugar desocupou-se).

Is mas the only option for “but”?

No. Alternatives include:

porém (more formal, often after a semicolon or comma)
no entanto (formal/neutral; typically starts a new clause)
só que (informal/colloquial) Example: A carruagem estava cheia; porém, esse assento ficou livre de repente.

Can I use a cleft construction for emphasis, like “It was suddenly that…”?

Yes: Foi de repente que esse assento ficou livre. This front-focuses the abruptness of the event and is idiomatic in European Portuguese.

Could I drop the article and say “Carruagem estava cheia…”?

No. In standard Portuguese you need the article: A carruagem estava cheia. Dropping it sounds like a headline or a note, not normal speech.