Here's why:
* Nouns are words that name people, places, things, or ideas. They are the core of the sentence, representing the entity performing the action or being described.
* Pronouns stand in for nouns. They act as substitutes for nouns that have already been mentioned or are understood within the context.
Examples:
* The cat sat on the mat. (Noun)
* She went to the store. (Pronoun)
While nouns and pronouns are the most common subjects, there are some exceptions:
* Gerunds: These are verbs ending in "-ing" used as nouns. Example: Swimming is my favorite activity.
* Infinitives: These are verbs preceded by "to." Example: To travel is my dream.
* Clauses: A clause is a group of words containing a subject and verb. Example: What you said is true.
However, it's important to note that these exceptions are less common than nouns and pronouns acting as subjects.