Keep me logged in until I sign out. There is no universal legal test of mental capacity or incapacity.
Laws vary from state to state, but some general principles apply everywhere.
Incapacity is always evaluated in connection with specific tasks. Different legal standards of capacity may apply to different tasks, such as capacity to do a will, to drive, to enter contracts, to manage money, or to make medical decisions. Second, there must be a finding that the disability prevents the person from performing activities essential to take care of his or her personal needs or property. Most courts will also insist that all feasible alternatives to guardianship have been explored before appointing a guardian. This is a free service.