grammar vs modify

grammar is a noun but modify is not a noun.

Word	Noun	Adjective	Verb	Adverb
grammar	Yes	No	No	No
modify	No	No	Yes	No

grammar (noun)	modify (noun)
the branch of linguistics that deals with syntax and morphology (and sometimes also deals with semantics)

grammar (verb)	modify (verb)
	make less severe or harsh or extreme
	add a modifier to a constituent
	cause to change; make different; cause a transformation