Also known as: M'Naghten test · M'Naghten rule · M'Naghten rules · McNaughton test · McNaghten test
Written by attorneys · grounded in primary & secondary sources — see below
A common-law test for legal insanity under which a defendant is entitled to acquittal if a disease of the mind caused a defect of reason such that the defendant lacked the capacity either to know the nature and quality of the act or to know that the act was wrong.
Meredith Maxwell suffered from schizophrenia that produced an overpowering urge to set fires. She deliberately ignited a warehouse while fully aware she was burning property and that the law forbade it. Because she retained the capacity to understand the nature of her act and its legal wrongfulness, the traditional M'Naghten test provided no defense even though her illness destroyed her ability to refrain.
Mohan Malhotra believed his neighbor was a government hologram rather than a person. He fired a rifle at the neighbor while knowing he was pulling a trigger but convinced the target could not be harmed. The delusion prevented him from grasping the physical nature of shooting a human being, satisfying the M'Naghten cognitive prong and supporting acquittal.
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No. The traditional test is strictly cognitive. A defendant who knows the nature and quality of the act and knows it is wrong remains criminally responsible even if mental illness made the conduct feel irresistible.
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The defendant must lack the capacity to recognize that society and the criminal law regard the conduct as wrongful. A sincere personal belief that the act is morally justified does not suffice if the defendant still understands society's contrary judgment.
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A delusion satisfies the test when it prevents the defendant from understanding that the victim is a real human being or that the physical act is causing harm to a person. In such cases the defendant does not comprehend the nature and quality of the conduct.
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No. The test requires proof that the disease caused a defect of reason at the precise time of the offense that eliminated the defendant's capacity to know the nature and quality of the act or its wrongfulness. A past diagnosis alone is insufficient.
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…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…