incapableness vs unfitness

incapableness and unfitness both are nouns.

Word	Noun	Adjective	Verb	Adverb
incapableness	Yes	No	No	No
unfitness	Yes	No	No	No

As nouns, unfitness is a hypernym of incapableness; that is, unfitness is a word with a broader meaning than incapableness:

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

Other hypernyms of incapableness include inability.

incapableness (noun)	unfitness (noun)
the quality of not being capable -- physically or intellectually or legally	the quality of not being suitable
lack of potential for development	lacking the power to perform
	poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)