Able><unable,ability><inability

[hongson]

please help me this question.My morphology tutor give us a week to answer his question, "able" is an adjective and the opposite of it is "unable",but the opposite of "ability"(noun) is "inability",so why there's a diffirence,exactly is the prefix "un" and "in".Please help me
Thank you so much

 

[Raymott]

Dear teacher,please help me this question.My morphology tutor give us a week to answer his question, "able" is an adjective and the opposite of it is "unable",but the opposite of "ability"(noun) is "inability",so why there's a diffirence,exactly is the prefix "un" and "in".Please help me
Thank you so much

What have you come up with in your research so far?