For criminal law, “insanity” has a special meaning. Legal tests for determining legal tests for determining insanity have been developed, but none have been universally accepted as valid.
The M’Naghten rule (1843)
Defendants must show that because of their mental illness, either they did not know what they were doing or they did not know it was wrong.
Critics say that it does not protect defendants who cannot control themselves because of mental illness.
Section 4.01 Model Penal Code
“A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of law.”