adj. 1) not being able to perform any gainful employment due to congenital disability, illness (including mental), physical injury, advanced age or intellectual deficiency. This is significant in claims for worker's compensation, disability insurance, or Social Security claims under "SSI." 2) lacking the ability to understand one's actions in making a will, executing some other document or entering into an agreement. A challenge to the validity of a will often turns on a claim that the person (now dead and unable to testify) lacked the capacity to understand what he/she owned, who were the "natural objects of his/her bounty" (close relatives primarily), that no one was able to dominate the testator's (will writer's) judgment so as to exert "undue influence." Mental weakness may show lack of capacity to make a will, as can fear, intimidation or persistent drunkenness. Example: an old lady is kept well supplied with whiskey for several months by her greedy sisters, who finally convince her to change the will from benefitting her children to benefitting them when she is drunk and fearful they will cut off her supply. A court would probably find she had lacked capacity to decide to make the latest version of the will.