Question: Shouldn't your be changed to you in the sentence Sarah was surprised at your leaving early ? Answer: In the example your is correct. Your is the possessive form of you and acts as the subject of the gerund leaving . In formal writing , when we want to show who or what is doing the action in a gerund (called the subject of the gerund ), we use the possessive form of a personal noun or pronoun in front of the gerund: Gord's winning the contest gives us all a reason to celebrate. Natalie objected to my borrowing her hockey stick. Your leaving early was a wise decision. In informal writing , there is a trend toward dropping the possessive before a gerund. We often use a simple noun or an object pronoun instead: We celebrated Gord winning the contest. Natalie objected to me borrowing her notes. Also, the possessive form may be important f...