falsify vs falsity

falsify is not a noun while falsity is a noun.

Word	Noun	Adjective	Verb	Adverb
falsify	No	No	Yes	No
falsity	Yes	No	No	No

falsify (noun)	falsity (noun)
	a false statement
	the state of being false or untrue

falsify (verb)	falsity (verb)
falsify knowingly
insert words into texts, often falsifying it thereby
prove false
make false by mutilation or addition; as of a message or story
tamper, with the purpose of deception