English grammar rule Possessive apostrophe
There are three ways to form the genitive (possessive) form of a noun: If it’s singular, add an apostrophe and an -s (the dog’s bone, Jimmy’s sandwich, the class’s trip). For plural nouns, simply add an apostrophe (the girl’s dress). You also can form a genitive by adding the preposition of (the queen of mean).
There is an exception: with inanimate objects, you can sometimes use the apostrophe to form a possessive, but in most cases you’ll want to use of instead.
Lastly, in some cases the context, rather than explicit mention, makes the context clear. For example, if you say I’m going to my Aunt’s, it means you’re going to your Aunt’s house.
Incorrect An hour later I found the pen in my sisters drawer. Correct An hour later I found the pen in my sister’s drawer. (one sister) Correct An hour later I found the pen in my sisters’ drawer. (more than one sister) Incorrect I’ll wait for you at my fathers. Correct I’ll wait for you at my father’s. Incorrect We’ve just seen the ad about that cars engine. Correct We’ve just gotten the announcement about that church’s schedule change. Correct We’ve just gotten the announcement about the schedule change of that church.