Here's why:
* Nouns are words that name people, places, things, or ideas. They are the core of the sentence, representing the entity that performs the action or is described.
* Pronouns take the place of nouns. They can also function as subjects, referring to a noun that has already been mentioned or is understood.
Examples:
* The dog barked. (Subject: "dog" - a noun)
* She ran to the store. (Subject: "she" - a pronoun)
* John and Mary went to the park. (Subjects: "John" and "Mary" - both nouns)
Important Note: While the subject is typically a noun or pronoun, there are exceptions, like clauses that can also act as subjects:
* What she said surprised everyone. (Subject: "What she said" - a clause)