incapableness vs incapable

incapableness is a noun but incapable is not a noun.

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

incapableness (noun)	incapable (noun)
the quality of not being capable -- physically or intellectually or legally
lack of potential for development

incapableness (adjective)	incapable (adjective)
	(followed by `of') lacking capacity or ability
	(followed by `of') not having the temperament or inclination for
	not meeting requirements
	not being susceptible to or admitting of something (usually followed by `of')