* Nouns: This is the most common type of subject.
* Example: *The dog barked loudly.*
* Pronouns: These stand in for nouns.
* Example: *He ran to the store.*
* Gerunds: These are verb forms ending in "-ing" that act as nouns.
* Example: *Swimming is my favorite exercise.*
* Infinitives: These are verb forms preceded by "to" that act as nouns.
* Example: *To travel is my dream.*
* Noun Clauses: These are groups of words that function as nouns.
* Example: *What you said surprised me.*
* Noun Phrases: These are groups of words that function as nouns.
* Example: *The big red truck drove down the street.*
Important Note: The subject of a sentence must be a noun or something acting as a noun. It cannot be an adjective, adverb, preposition, or conjunction.