1. Wanting in ability or qualification for the purpose or end in view; not large enough to contain or hold; deficient in physical strength, mental or moral power, etc.; not capable; as, incapable of holding a certain quantity of liquid; incapable of endurance, of comprehension, of perseverance, of reform, etc.
4. Unqualified or disqualified, in a legal sense; as, a man under thirty-five years of age is incapable of holding the office of president of the united States; a person convicted on impeachment is thereby made incapable of holding an office of profit or honor under the government.
incapable is often used elliptically. Is not your father grown incapable of reasonable affairs? (Shak)