Learn Portuguese (Portugal): A perseverança é crucial a fim de proteger as ruínas. - Perseverance is crucial in order to protect the ruins.

In Portuguese, abstract nouns (like perseverança, amor, or liberdade) require a definite article when used in a general or universal sense. While English drops the article for general abstract concepts, Portuguese keeps it.

I know para means "in order to". How is a fim de different?

A fim de and para both express purpose and can often be used interchangeably before an infinitive. However, a fim de is a bit more formal and emphatic. It directly translates to "in order to" or "with the explicit purpose of," whereas para is your everyday "to."

This lesson focuses on the personal infinitive. Why is proteger left in the impersonal (unconjugated) infinitive here?

We leave it impersonal because the subject performing the action is general (meaning "for anyone to protect the ruins"). If we wanted to specify exactly who needs to protect them—for example, "in order for us to protect the ruins"—we would conjugate it into the personal infinitive: a fim de protegermos as ruínas.

I sometimes see afim written as one word. Could I write afim de here?

No, though that is a very common spelling mistake even among native speakers! A fim de (three words) is a prepositional phrase meaning "in order to." Afim (one word) is an adjective meaning "similar" or "related" (sharing the same root as the English word "affinity").