Here's why:
* Verbs express action or a state of being. Examples: run, jump, sleep, exist.
* "Not" is an adverb. It modifies verbs, adjectives, or other adverbs to negate them.
Examples:
* Verb: I run.
* Adverb: I do not run. ("Not" modifies the verb "run" to negate it.)
* Adjective: The house is not big. ("Not" modifies the adjective "big" to negate it.)
Let me know if you have any other grammar questions!