No Apostrophe With Possessive Pronouns
The Apostrophe
Rulebase Summary
Do not use an apostrophe with any of the possessive personal pronouns: mine, yours, his, hers, its, ours, theirs, whose. These words are already possessive and never take an apostrophe.
Examples
A. The dog wagged it's tail when I walked in.
A. The dog wagged its tail when I walked in.
'Its' is a possessive pronoun and never takes an apostrophe — 'it's' means 'it is.'
A. I don't know who's file this is.
A. I don't know whose file this is.
'Whose' is a possessive pronoun — 'who's' means 'who is.'
Transcript Notes
Do NOT use an apostrophe with any of the following possessive personal pronouns: mine, yours, his, hers, its, ours, theirs, whose. These are inherently possessive and never take an apostrophe. The most common error is 'it's' (which is the contraction of 'it is') confused with 'its' (the possessive pronoun). Spelling this contraction wrong in any written matter is, as Morson puts it, 'punishable by death.'
Style Guide References (2)
Morson's
BGGP