“whose” vs. “who's”
If you can expand the word to "who is" or "who has" and it still makes sense, write "who's"; if the sentence shows ownership, write "whose" with no apostrophe.
whose
"Whose" is a possessive pronoun asking or showing ownership ("whose book is this?," "the author whose novel won the prize"), and like every other possessive pronoun, it never takes an apostrophe. "Whose" descends from Old English "hwæs," the possessive form of "hwa" (who), part of the same very old possessive-pronoun system that also produced "his" and "its" without an apostrophe.
who's
"Who's" is a contraction of "who is" or "who has" ("who's calling?," "who's finished the assignment?"), the apostrophe marking the omitted letters exactly as it does in "it's" or "you're." "Who's," the contraction of "who is" or "who has," only became standard written practice once apostrophe-marked contractions became common typographic convention in the 17th and 18th centuries, layered on top of an interrogative pronoun, "who," that itself dates back to Old English "hwa."
The real distinction
This pair follows the identical logic as its/it's: English possessive pronouns (his, hers, its, whose, theirs) never take an apostrophe, while contractions always do, marking dropped letters. "Whose" and "who's" happen to be a particularly easy pair to mix up because "who's," with its apostrophe, looks like it should be the possessive form by analogy with regular nouns ("the dog's bone"), even though possessive pronouns don't follow that pattern at all. This pair is frequently grouped by grammar teachers alongside its/it's and your/you're as the three classic possessive-pronoun-versus-contraction mix-ups in English, all sharing the identical underlying logic: genuine possessive pronouns never take an apostrophe, no matter how much they might resemble a possessive noun that would. Style guides for professional editing typically treat all three as equally serious, equally common errors worth a dedicated final proofreading pass, precisely because none of them can be reliably caught by an ordinary spell-checker. Some style guides note that "whose" has, somewhat unusually for a possessive pronoun, extended in modern usage to refer not just to people but to things as well ("the company whose profits fell"), a genuinely accepted usage that a strict older prescriptive rule once discouraged in favor of the clunkier "of which," though virtually no contemporary style guide still enforces that older restriction. Because this pair follows the identical underlying logic as its/it's and your/you're, writing instructors often teach all three possessive-pronoun-versus-contraction pairs together as one unified lesson rather than as separate, unrelated rules to memorize.
Examples with “whose”
- Whose jacket is this on the chair?
- I don't know whose idea it was originally.
- The man whose car was towed is furious.
- Whose turn is it to pay for dinner?
- She's the artist whose work is on display.
- Whose responsibility is it to lock up?
- The student whose essay won got a scholarship.
- Whose phone keeps ringing in the meeting?
Examples with “who's”
- Who's coming to the party tonight?
- Who's finished the assignment already?
- Do you know who's in charge here?
- Who's been using my charger?
- Who's ready to leave for the airport?
- I wonder who's going to win this year.
- Who's responsible for booking the venue?
- Who's up for a walk after lunch?
Memory trick
Test it by expanding to "who is": "who's calling" becomes "who is calling," which works, so the apostrophe stays; but "who's book is this" would become "who is book is this," which is nonsense, so the correct word there is "whose" with no apostrophe at all. A further practical check beyond the "who is" expansion: notice what the word introduces — "whose" always sits directly in front of the thing being owned ("whose car," "whose idea"), while "who's" sits in front of a description of what someone is doing or is like ("who's coming," "who's ready"), a quick structural glance that works even when the full expansion test feels awkward to run mentally. One last practical check: if deleting the word and inserting "who is" in its place produces a complete, sensible question or clause, you need the contraction; otherwise, the possessive "whose" is what the sentence requires.