Learn Italian: I bambini si sono addormentati prima che la favola finisse. - The children fell asleep before the fairy tale ended.

The tense in the second part of the sentence depends on the first part. Because the main action happened in the past (si sono addormentati), the sequence of tenses rule says we must use a past tense in the subjunctive clause too. We use the imperfect subjunctive (finisse) to show the fairy tale's ending was happening at the same time as, or right after, them falling asleep.

Does prima che always trigger the subjunctive?

Yes! The phrase prima che (before) always requires the subjunctive in Italian. This is because when something happens "before" another event, that second event hasn't actually happened yet in the timeline of the sentence, making it an anticipated or uncertain action rather than a hard fact.

How would this sentence change if the main action was in the present tense ("The children fall asleep")?

If the main clause is in the present tense (I bambini si addormentano), the sequence of tenses shifts. Because the main verb is in the present, you would use the present subjunctive for the second half: ...prima che la favola finisca.

Why does addormentati end in an -i here?