Ah, that is a great point. Of course you know I meant that the rule of not apostrophizing its is backwards from the more common case of personal pronouns. Okay, so the possessive pronouns don’t use apostrophes and personal pronouns do. And its and whose are possessive pronouns, or possessive determiners. Is that the whole apostrophe rule? Are there any other cases or exceptions for possession? Do all indefinite pronouns use apostrophes, e.g., it’s anybody’s guess?