The legal definition of insanity/mental illness applies the M’Naghten Rule, formulated in 1843 and derived from English law. It says that: a person is innocent by reason of insanity if at the time of committing the act, [the person] was laboring under a defect of reason from disease of the mind as not to know the nature and quality of the act being done, or if he did know it, he did not know that what he was doing was wrong. There are variations of this legal definition by state, and some states have abolished the insanity defense.