1. Criminal law. The doctrine that a person is not criminally responsible for an act when a mental disability prevented the person from knowing either
(1) the nature and quality of the act or
(2) whether the act was right or wrong.
The federal courts and most states have adopted this test in some form. McNaghten’s Case, 8 Eng. Rep. 718 (H.L. 1843). — Also spelled McNaughten rules; M’Naghten rules; M’Naughten rules. — aka right-and-wrong test; right-wrong test. 
M’Naghten Test – The right and wrong test of criminal responsibility, the terminology being taken from the title of an English Case. M’Naghten’s Case. 10 Clark & F 200, 8 Eng Reprint 718.
right and wrong test – A test, applied in determining responsibility for an act otherwise constituting criminal homicide, according to the ability or capacity of the accused to distinguish between right and wrong. 26 Am J1st Homi § 79.
The test of criminal responsibility of a mentally deficient person according to whether the accused was laboring under such a defect of reason from disease of the mind as not to know the nature and quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong. 21 Am J2d Crim L § 33.
The test of criminal responsibility of an infant according to whether or not he knew that the act constituting the offense was wrongful. 21 Am J2d Crim L §27.
A matter of moral right and wrong or, according to other authorities, right or wrong within the intendment of law. 21 Am J2d Crim L § 35.
A test according to whether the accused knows the difference between right and wrong, can understand his relation to others, and that which others bear to him, and has knowledge of the nature of his act so as to perceive its consequences to himself and others. 21 Am J2d Crim L 4. 
M’Naghten rule – A test employed in a number of jurisdictions for determining whether a criminal defer» dant had the capacity to form criminal intent at the time he committed the crime of which he is accused. Specifically, the M’Naghten rule is that an accused is not criminally responsible if he was laboring under such a defect of reason from disease of the mind that he either did not know the nature of his act or, if he did, that he did not know it was wrong. The M’Naghten rule is also referred to as the right and wrong test. 
Excerpt from Rollin M. Perkins & Ronald N. Boyce’s Criminal Law (3d ed. 1982):
“Four points stand out and should be understood whenever reference to M’Naghten is made other than in regard to procedure.
(1) It applies only in case of a defect of reason, from disease of the mind, and without this the following do not apply except that ‘disease’ as so used will be interpreted to include congenital defect or traumatic injury.
(2) If, because of this ‘defect of reason,’ the defendant did not know what he was doing he is not guilty of crime.
(3) Even if the defendant knew what he was doing he is not guilty of crime if, because of this ‘defect of reason,’ he did not know he was doing wrong.
(4) If the defendant acted under an insane delusion, and was not otherwise insane, his accountability to the criminal law is the same as if the facts were as they seemed to him to be.” 
Disclaimer: All material throughout this website is compiled in accordance with Fair Use.
: Black’s Law Dictionary Deluxe Tenth Edition by Henry Campbell Black & Editor in Chief Bryan A. Garner. ISBN: 978-0-314-62130-6
: Ballantine’s Law Dictionary with Pronunciations
Third Edition by James A. Ballantine (James Arthur 1871-1949). Edited by William S. Anderson. © 1969 by THE LAWYER’S CO-OPERATIVE PUBLISHING COMPANY. Library of Congress Catalog Card No. 68-30931
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