The M'Naughten Rule

The M'Naughten Rule is a legal standard used to judge whether an offender is insane (and could thus base a defense on “not guilty by reason of insanity”). The rule states that individuals are not guilty of crimes if they lack awareness of their actions. Part of this awareness concerns knowledge of the wrongfulness of the act. An individual who is deemed not responsible for his or her actions cannot be held accountable for criminal conduct.

The origination of this rule can be traced back to 1843. Daniel McNaughten created controversy when he was tried and acquitted for the murder of the British Prime Minister's secretary, Edward Drummond. Upon investigation, it became apparent that Daniel had committed the murder due to a belief that the government was persecuting him. During the hearing, medical experts provided a substantial history of mental illness in the offender, which was irrefutable by the prosecutor as grounds for the insanity defense. As a result, McNaughten was acquitted and sent to a mental hospital for treatment until his death 20 years later.

For an insanity defense to be an appropriate plea, it must meet several conditions. While committing the crime, the accused must have (a) acted under a defect of reason (b) from disease of the mind so as (c) not to have had knowledge of the wrongfulness of the act.

Since the initiation of the M'Naughten Rule in 1843, there have been few amendments to the aforementioned standards. Today, the insanity defense is still an option for defense in a court of law.