Insanity Defense

The defense excusing defendants who lacked capacity when offending

Overview

The modern rules date to the 1843 M Naghten case in England, asking whether the defendant knew the nature and quality of the act or that it was wrong. Later tests added irresistible impulse and, in the American Model Penal Code, substantial capacity to appreciate wrongfulness or conform conduct. The defense is rarely raised and rarely succeeds, yet politically prominent, and several American states abolished or narrowed it after the 1982 Hinckley acquittal. Alternatives include guilty but mentally ill verdicts.