The Possessives Its and Your

Apostrophes usually mark possession: the dog's bone. But it's, you're, and who's break that pattern on purpose. The apostrophe there isn't showing ownership at all — it's standing in for a missing letter, because the word is a contraction. 'It's' is 'it is' with the i dropped. 'You're' is 'you are' with the a dropped. 'Who's' is 'who is' with the i dropped. Its, your, and whose, with no apostrophe, are the possessive forms, doing the same job as 'his' or 'her' — and 'his' never takes an apostrophe either, which is the cleanest proof that possession and apostrophes aren't actually linked for pronouns.

The test is mechanical, not a matter of feel. Take the marked word, expand it to 'is' or 'are,' and read the sentence aloud. 'The museum closed it is west wing' crashes immediately, so the possessive its is correct. 'You are going to need more signatures' reads fine, so you're is correct. This works because English pronoun possessives — its, your, his, her, whose, theirs — are a closed set that never takes an apostrophe, unlike noun possessives like the dog's or the museum's.

This sits next to every other agreement-and-word-choice question on usage conventions: the sentence is already built, and one word has to fit the slot grammatically, not just sound right. Whose and who's extend the same test to a third pair, so once the read-aloud trick is automatic, all three pairs fall the same way.