Here's why:
* Pronouns replace nouns: They stand in for nouns to avoid repetition. For example, instead of saying "John went to the store, and John bought some milk," you can say "John went to the store, and *he* bought some milk."
* Pronouns function like nouns in sentences: They act as subjects, objects, and complements, just like nouns.
Examples:
* Subject: *She* went to the park.
* Object: I saw *him* at the library.
* Complement: The winner is *she*.
Let me know if you have any other questions!