Learn Hardcore Portuguese (Portugal): Se abrirmos a porta sem a chave, o alarme dispara. - If we open the door without the key, the alarm goes off.

Abrirmos is actually the personal infinitive of abrir for nós (we), not the present subjunctive. The personal infinitive adds endings to the basic infinitive to show the subject, so abrirmos literally means “that we open.” The present subjunctive form for “we open” would be abramos, which is not used here.

Why don’t we include nós before abrirmos?

Portuguese is a pro-drop language: the verb ending -mos already signals first person plural (“we”). Including nós (“we”) is grammatically correct but usually unnecessary unless you want extra emphasis (e.g. Se nós abrirmos…).

Could we use Se abramos instead of Se abrirmos?

No. In modern European Portuguese, a real (“zero”) conditional with se takes the present indicative or the personal infinitive, never the present subjunctive (abramos). Hence Se abrirmos… is the correct form.

Why is there a comma before o alarme dispara?

When the if-clause (a subordinate clause) comes first, standard punctuation in Portuguese places a comma before the main clause. If you flipped the order—O alarme dispara se abrirmos a porta sem a chave—you would omit the comma.

Why use a porta and a chave with definite articles?

Portuguese typically uses definite articles before nouns where English might not. To say “the door” you need a porta, and “the key” is a chave. If you wanted to say “a door” or “a key” in Portuguese, you’d use uma porta or uma chave respectively.

Can we drop the article and say sem chave?

You could say sem chave to mean “without any key” in a very general sense. But here it’s the specific key for that door, so you need sem a chave (“without the key”).

Why is dispara used for the alarm?

In Portuguese, disparar can mean “to trigger” or “to go off” when referring to alarms (as well as guns or cameras). So o alarme dispara means “the alarm goes off.”

Why is the present tense used instead of future or past?

This sentence expresses a general truth or real condition (“if X happens, Y always happens”). In Portuguese, such zero-conditionals use the present indicative in both clauses—just like English zero-conditionals (“If we heat water to 100 °C, it boils”).