Here's why:
* Subject Pronouns: These words represent the person or thing performing the action in a sentence (e.g., I, you, he, she, it, we, they).
* Verbs: These words express the action or state of being in a sentence.
Example:
* Correct: She walks to school. (Subject pronoun "She" replaces the noun "Mary" and the verb "walks" expresses the action.)
* Incorrect: She school. (This doesn't make sense because "She" is a subject pronoun, not a verb, and "school" is an object, not an action.)
To summarize, subject pronouns can only replace nouns, not verbs.