Sometimes two tricky areas of English usage – pronouns and apostrophes – combine to create an extra-tricky pair of words. One example is its and it’s, which cause frequent trouble, and so it is with who’s and whose. It’s not just learners of English who confuse them – experienced and native users of the language also slip up. So let’s try and sort it out.
Who’s is short for who is or who has. If you remember only this from what I write here, you’ll avoid making the error. Consider these lines: Who’s in charge here? We want someone who’s always ready. Who’s been eating my porridge? And these set phrases: who’s who; look who’s talking; show someone who’s boss. In each one, you can replace who’s with who is, or occasionally who has.
Whose is the possessive form of who, meaning, more or less, ‘of whom’ or ‘of which’. There’s usually a verb nearby, but it’s not part of the word as it is in who’s. We see whose in lines like Whose shoes are these? and I’ve a friend whose cat wakes them. Fixed expressions with whose include whose side are you on and the TV show Whose Line Is It Anyway?
Who’s and whose are homophones, both pronounced /huːz/, and they both involve who. So they’re easily mixed up. A Get It Right! box in our entry for who describes the usual error: using who’s instead of whose. (There’s also a usage note in the entry for whose.) We’re so used to adding apostrophe-s to show possession (Mary’s art; the dog’s toy) that it seems like who’s and it’s should be possessive as well – but they’re not. This may underlie the error in many cases.
The mistake even appears, not infrequently, in edited texts: I’ve come across ‘who’s fault’, ‘who’s work’, and ‘who’s autograph’ in books, and, in newspapers, ‘who’s hit [single]’ and – the opposite error – ‘someone whose recently taken an interest’. In all these cases the error slipped past professional writers, sub-editors, and proofreaders – a sign of how sneaky it is.
Who, incidentally, is the only relative pronoun with a possessive case in standard English, which is why it’s used as the possessive form of that and which (though the curious, non-standard variant thats appears now and then). Some prescriptive critics say that whose should only be used of people – that an idea whose time has come, for instance, is incorrect or substandard. But that’s a myth whose time is up.