I’ve said it before, and I’ll say it forever…the English language is confusing, contradictory, and full of exceptions to the rules. Let’s look at two words – who’s and whose.
We often think of the apostrophe as indicating ownership (this is Jodi’s computer), but in this case, the apostrophe means letters have been omitted. Who’s is a contraction, and it’s ONLY EVER a contraction. Who’s = who is: Who’s (who is) buying a new computer?
The word whose, then, deals with ownership: Whose computer is this?
The easiest way to determine which one to use is to ask yourself if using who is in place of the word makes sense. For example, would it make sense to say: “Who’s (who is) computer is this?” Nope, that sounds pretty silly, so we know it should be whose.