Learn Finnish: Vankilasta paettiin yöllä. - Someone escaped from prison at night.

Paeta (to escape) is a type 6 verb. To make the past passive for verbs of types 4, 5, and 6, we take the verb stem (drop the -ta or -tä from the infinitive to get pae-) and add the past passive ending -ttiin. This gives us paettiin.

The translation says someone escaped, but isn't paettiin the passive voice?

Yes! In Finnish, the passive voice doesn't just mean an action was done to something; it specifically means the action was done by an unspecified person. Translating it as someone did the action is often the most natural way to express this in English.

Why do we use the -sta ending for vankilasta?

The elative ending -sta means out of or from inside something. Because a prison (vankila) is a closed building, the escape happened from inside it. If they had escaped from an open area like a yard, we would typically use the outer location case -lta (from).

Why does yö (night) have the -llä ending?

The adessive case ending -llä (on/at) is often used with parts of the day to indicate when an action happened. Just like aamulla means in the morning, yöllä is the standard way to say at night or during the night.