incapability vs inability

incapability and inability both are nouns.

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

As nouns, inability is a hypernym of incapability; that is, inability is a word with a broader meaning than incapability:

incapability: the quality of not being capable -- physically or intellectually or legally
inability: lacking the power to perform

Other hypernyms of incapability include unfitness.

incapability (noun)	inability (noun)
the quality of not being capable -- physically or intellectually or legally	lacking the power to perform
lack of potential for development	lack of ability (especially mental ability) to do something