Here's why:
* Possessive pronouns show ownership or belonging. Examples include: mine, yours, his, hers, its, ours, theirs.
* Nominative case is used for subjects and predicate nominatives (words that rename the subject). While possessive pronouns don't directly act as subjects, they function similarly in showing ownership.
Example:
* "That book is mine." ("Mine" indicates ownership of the book.)
Let me know if you have any other pronoun questions!