Here's why:
* Pronouns stand in for nouns. They refer to a person, place, or thing already mentioned or understood.
* Common nouns are general names for people, places, or things (e.g., dog, city, book).
Examples:
* Pronoun: "She went to the store." (She refers to a specific person already understood.)
* Common noun: "The dog barked at the mailman." (Dog is a general name for a type of animal.)