Learn Polish: Według szefa, kelner, upuściwszy tacę, musi za nią zapłacić. - According to the boss, the waiter, having dropped the tray, must pay for it.

The participle upuściwszy (having dropped) is an adverbial participle. A strict rule in Polish is that its implied subject must perfectly match the subject of the main clause. Since kelner (the waiter) is the subject of the main verb musi (must), the waiter is grammatically locked in as the one who dropped the tray. If the boss had dropped it, we would have to rewrite the sentence using a normal subordinate clause.

Why do we use upuściwszy here instead of an -ąc participle like upuszczając?

Upuściwszy is a perfective anterior participle, recognizable by the -wszy ending attached to a perfective verb base. It explicitly shows that the action of dropping the tray was fully completed before the action in the main clause took place. If we used the imperfective upuszczając (dropping), it would imply the two actions were happening simultaneously, meaning he has to pay for the tray right in the middle of dropping it.

Why does the sentence use za nią for 'for it' instead of za niej?

The phrase zapłacić za (to pay for) requires the following noun or pronoun to be in the accusative case. The pronoun refers back to taca (the tray), which is feminine. The normal accusative feminine form of ona is ją, but whenever a pronoun directly follows a preposition in Polish, it gains an extra n- at the start, making it nią.

Are the commas around upuściwszy tacę strictly necessary?