Also known as:M'Naghten rule · M'Naghten rules · McNaghten rule · M Naghten rule · M'Naghten test · insanity defense standard
Written by attorneys — see sources below.
A common-law test for criminal insanity that excuses liability when a mental disease causes a defect of reason such that the defendant either did not know the nature and quality of the act or did not know that the act was wrong. The test focuses exclusively on cognitive capacity at the time of the offense. Loss of behavioral control caused by mental illness does not satisfy the standard.
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How its tested
Common Examples
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Hallucinations and Retained Awareness
Monica Morgan, a museum curator with chronic psychosis, burned several paintings after drinking heavily. She told police she believed the paintings contained evil spirits and that destroying them fulfilled a moral duty. Monica also calmly acknowledged that colleagues and the public would view the destruction as seriously wrongful. Under the traditional M'Naghten rule the court rejected her insanity defense because she retained the capacity to recognize that society regarded her conduct as wrong.
Delusional Belief About Nature of Act
Miguel Mendoza, a ground technician with severe psychosis, removed critical fasteners from a passenger jet. He believed the jet was a decommissioned museum display that would never fly. Medical experts confirmed the delusion resulted from mental disease. Under the traditional M'Naghten rule the jury could acquit if it found that the disease prevented Miguel from understanding the true nature and quality of disabling an aircraft carrying passengers.
Durham v. United States214 F.2d 862, 874–75 (D.C.Cir.1954)
Monte Durham was convicted of housebreaking by the District Court of the District of Columbia sitting without a jury. The prosecution proceeded on a charge arising from an incident on July 13, 1951, in which Durham was found in a house.
Durham's history included discharge from the Navy in 1945 at age seventeen following a psychiatric examination revealing a profound personality disorder rendering him unfit for service. In 1947 he pleaded guilty to violating the National Motor Theft Act and was placed on probation for one to three years. In January 1948, as a result of a conviction in the District of Columbia Municipal Court for passing bad checks, the District Court revoked his probation and he commenced service of his Motor Theft sentence. His conduct within the first few days in jail led to a lunacy inquiry in the Municipal Court where a jury found him to be of unsound mind. Upon commitment to St. Elizabeths he was diagnosed as suffering from 'psychosis with psychopathic personality.' He experienced multiple discharges and readmissions to St. Elizabeths between 1949 and 1951, including a conditional release in June 1950 that he violated, and a further lunacy finding in 1951.
Following the July 1951 housebreaking, Durham was indicted in October 1951 and adjudged of unsound mind based on psychiatrists' affidavits diagnosing psychosis with psychopathic personality. He underwent subshock insulin therapy during a six-month commitment ending in February 1953, after which Dr. Silk certified him mentally competent to stand trial and able to assist counsel.
At the ensuing trial, the prosecutor expressed a plan to allow Durham to raise an insanity defense on this charge. The court accepted waivers of jury trial and additional competency proceedings despite Durham's expressed desire for further hospitalization. Testimony included that of Durham's mother regarding his post-May 1951 behavior and a psychiatrist who examined him in September 1951 and opined on his mental condition around the time of the offense. The trial court found the defense of insanity not established under the prevailing standards.
The appeal reached the United States Court of Appeals for the District of Columbia Circuit.
Does an inability to control one's conduct satisfy the traditional M'Naghten test?
No. The traditional M'Naghten rule examines only cognitive capacity. A defendant who understood the nature and quality of the act and knew it was wrongful remains criminally responsible even if mental illness made the conduct impossible to resist.
Supporting sources
Is a sincere personal belief that the conduct was morally right enough for an insanity acquittal under M'Naghten?
No. The defendant must lack the capacity to recognize that society regards the conduct as wrong. A personal moral belief that the act was justified does not excuse liability when the defendant still understood society's contrary judgment.
Supporting sources
What must a defendant prove to obtain an acquittal under the traditional M'Naghten rule?
The defendant must prove a disease of the mind caused a defect of reason that left the defendant unable either to understand the nature and quality of the act or to know that the act was wrongful as society defines wrongfulness.
Supporting sources
214 F.2d 862, 874–75 (D.C.Cir.1954)
…64-68, 109-47 (1933); Leland v. State of Oregon , 1952, 343 U.S. 790, 800, 72 S.Ct. 1002, 96 L.Ed. 1302. 'In five States the M'Naghten Rules have been in substance re-enacted by statute.' Royal Commission Report 409; see, e.g., Sec. 1120 of the New York Penal Law (McKinney Consol. Laws, c.40) which provides that a person is not…