Learn Hardcore Portuguese (Portugal): Para ficares mais seguro, fecha a porta com chave.

Portuguese has two infinitive forms: the impersonal infinitive (ficar) and the personal infinitive (ficares, ficarmos, etc.). Here, because you’re specifically telling tu what to do (“so that you become safer”), you use the personal infinitive ficares, which carries the -es ending for “tu.” If you said para ficar, it would be generic (“in order to become safe”) without pinpointing you as the subject.

What exactly is the personal infinitive, and why use it here?

The personal infinitive lets the infinitive verb agree with a specific subject. Its forms for “tu” end in -es, for “nós” in -mos, and so on. You use it when:

The subject of the infinitive is clear and identical to the main clause’s subject.
You want a concise way to express “in order for X to do Y.”
In para ficares mais seguro, the subject tu is understood, so we pick ficares over a full subordinate clause like para que tu fiques.

Why is fecha used here, and what form of the verb is it?

Fecha is the affirmative imperative (command) of fechar for tu. In European Portuguese, the tu-imperative of regular -ar verbs matches the third-person singular of the present indicative (tu fechas → drop the s → fecha). It directly tells someone familiar (“you”) to lock/close the door.

Why isn’t the pronoun tu used before fecha?

Portuguese commonly omits subject pronouns when the verb ending clearly indicates the subject. Here, fecha inherently signals “tu,” so adding tu (for instance, tu fecha) is grammatically correct but redundant and less idiomatic.

Why do we say com chave instead of com a chave?

After the preposition com (“with”), Portuguese often drops the definite article in set expressions. Com chave literally means “with key,” i.e. “lock it with a key.” You could use com a chave if you want to emphasize a particular, known key, but in everyday speech fecha a porta com chave is shorter and more idiomatic.

What does mais seguro mean here? Could I say mais em segurança?

Mais seguro is an adjective phrase meaning “safer” or “more secure.” Although em segurança (“in safety”) is valid, ficar mais em segurança sounds heavier. Native speakers prefer ficar mais seguro to convey “becoming safer.”

Can I use trancar a porta instead of fechar a porta com chave?

Yes. Trancar means “to lock.” So tranca a porta (tu-form) is a more direct way to say “lock the door.” Fechar a porta com chave is literally “close the door with a key” and equally correct, but trancar a porta is briefer.

Could I have used para que fiques instead of para ficares?

Definitely. Para que fiques mais seguro uses the present subjunctive fiques with the conjunction que, and it’s perfectly correct. However, since the subject is the same in both clauses, para ficares (personal infinitive) is more concise and common in spoken European Portuguese.