Dear Geist,

Help! I need a trick to remember whether to write “who's” or “whose.”

—Alice in Writerland, Cyberspace

Dear Alice,

You're in good company! Who's and whose have been confounding writers for a very long time. Whose is the possessive (Whose dog is that?). But who's looks like a possessive because it ends with an apostrophe and s, and because the two words are pronounced exactly the same way.

In fact, who's is a contraction—a word containing an apostrophe that stands in for one or more omitted letters. Who's is a short form of who is or who has. That's your trick: look for the apostrophe. If there is one, it will remind you of the omitted letters, which will unambiguously remind you of what the meaning is, and isn't.

—The Editors