Here's why:
* Noun: A noun is a word that names a person, place, thing, or idea (e.g., dog, school, book, happiness).
* Pronoun: A pronoun is a word that replaces a noun (e.g., he, she, it, they, this, that).
* Noun Phrase: A noun phrase is a group of words that functions as a noun. It typically includes a noun (the head of the phrase) and may include other words that modify or describe the noun (e.g., adjectives, articles, prepositions, etc.).
Examples:
* Noun: The dog barked.
* Pronoun: It barked.
* Noun Phrase: The big, brown dog barked.
In the last example, "the big, brown dog" is the noun phrase that acts as the subject of the sentence, replacing the simple noun "dog".