Breakdown of Dans la voiture, il faut mettre sa ceinture.
la voiture
the car
dans
in, inside
son
his/her/its (son, sa, ses)
il
it (impersonal subject)
Questions & Answers about Dans la voiture, il faut mettre sa ceinture.
Why does the sentence use il faut when the English translation says 'you must'?
Why is the verb mettre in its infinitive form?
When you want to say that a specific action is necessary, you follow il faut directly with an infinitive (the unconjugated dictionary form of the verb). Here, il faut mettre means 'it is necessary to put on'.
Why does it say sa ceinture (his/her belt) instead of ta or votre (your belt)?
Because il faut is an impersonal rule ('one must'), French uses the third-person possessive adjective sa to mean 'one's'. Literally, it translates to 'one must put on one's seatbelt'. The English translation uses 'your' just because it sounds much more natural in English.