M’Naghten Rules

In the United States, the concept of the Insanity Defense  began with The M’Naghten Rules, first conceived by British courts in 1843 and adopted with almost not alteration. The M’Naghten Rules were created as a response to the murder of Edward Drummond and attempted assassination of the British Prime Minister, Robert Peel by Daniel M’Naghten .

The Case

M’Naghten had believed, at the time of the attack, that the Prime Minister was conspiring to kill him. He shot and killed Drummond, aid to the Prime Minister, mistakenly believing him to be the Prime Minister. His delusions and erratic behavior at the time of trial convinced the court that he did not understand the immorality of his actions. He was placed into a mental-health facility for the rest of his life. The lack of a conviction caused a social uproar which led to the exploration of the concept of insanity as it applied to criminal acts. From this examination came the M’Naghten Rules.

The actual record of the case is available here: http://wings.buffalo.edu/law/bclc/web/mnaghten.htm

The Rules

The M’Naghten Rules stated that a person should not be held responsible for their actions if, because of a mental defect, he (i) did not know that his act would be wrong; or (ii) did not understand the nature and quality of his actions. Within these statements there was no defense for simple ‘loss of control’. They are comparatively strict and tend to center around the defendant’s cognitive understanding of his or her actions. “Did they know what they were doing at the time of the crime and if so, did they understand that it was wrong?”.  The burden of proof rests on the party relying upon the defendant’s insanity; that is to say, the defense must prove that at the time of the unlawful act, he or she did not understand their actions or did not know they were wrong.


The M’Naghten Rules are still the standard to which many states hold their defendants.


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