inability vs incapacity

inability and incapacity both are nouns.

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

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

inability (noun)	incapacity (noun)
lacking the power to perform	lack of physical or natural qualifications
lack of ability (especially mental ability) to do something	lack of intellectual power