Here's why:
* Adjectives describe or modify nouns and pronouns. They provide more information about the noun or pronoun they're attached to.
* Pronouns stand in for nouns. They take the place of a noun to avoid repetition.
Example:
* "He" (pronoun)
* "That tall man" (adjective modifying the pronoun "he")
Therefore, "tall" is the adjective modifying the pronoun "he" in the example.