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M'Naghten Rule: Definition & History

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  • 0:04 Legal Insanity
  • 0:26 Definition
  • 1:24 History
  • 3:32 Lesson Summary
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Lesson Transcript
Instructor: Benjamin Truitt
The M'Naghten rule forms the foundation of the modern insanity defense plea. The test was to determine if the defendant in a criminal case knew that his or her actions were wrong and illegal at the time of the act.

Legal Insanity

The prospect of murder seems like the device of an unsound mind. Sane and normal people do not normally kill and hurt one another, which begs the question: Why aren't all murderers found not guilty by reason of insanity? The answer lies in the difference between clinical mental illness and legal insanity.

Definition

One of the cornerstones of legal insanity is the M'Naghten rule, a test that determines whether or not a defendant is criminally liable for his or her actions if he or she suffers from mental illness.

The M'Naghten rule requires that, should a person who commits a crime be unable to recognize that the crime is morally or legally wrong due to mental disease or mental defect, they should be found not guilty by reason of insanity. This rule, as applied in English and American law, distinguished criminals based on their capacity to recognize right and wrong to determine legal sanity and not whether they had a mental illness. Consider the example of Ted Bundy who was clearly insane and a sociopath when he raped and murdered women. However, Bundy knew that what he was doing was wrong and that his actions were illegal. And he even tried avoiding capture. In this case, the M'Naghten test would find that, while clinically insane, Bundy was legally sane.

History

On a chilly London afternoon in 1843, Edward Drummond, the secretary of Prime Minister Robert Peel, was shot to death by Daniel M'Naghten. When apprehended by police, M'Naghten gave paranoid and delusional reasons why he shot Drummond. The court decided, in listening to the evidence, that M'Naghten was not able to understand the nature of the act he committed. M'Naghten was so delusional, he did not even recognize that he had done anything wrong. This formed the basis of the modern insanity defense, or the M'Naghten rule.

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