knowledge vs inability

knowledge and inability both are nouns.

Word	Noun	Adjective	Verb	Adverb
knowledge	Yes	No	No	No
inability	Yes	No	No	No

As nouns, inability is a hyponym of knowledge; that is, inability is a word with a more specific, narrower meaning than knowledge:

knowledge: the psychological result of perception and learning and reasoning
inability: lack of ability (especially mental ability) to do something

knowledge (noun)	inability (noun)
the psychological result of perception and learning and reasoning	lacking the power to perform
	lack of ability (especially mental ability) to do something