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The M'Naghten Rule

Attorneys may use various criminal defense strategies when defending a client in a criminal case, but despite how movies and television portray it, the insanity defense isn't easy to use. A criminal defendant must meet the jurisdiction's definition of legal insanity for a court to find them not guilty because of insanity.

Courts will determine legal insanity by applying one of the following tests/rules:

It's not up to the court to decide which test to apply. Instead, the laws of a particular state determine it. This article focuses on the M'Naghten Rule for determining legal insanity.

History and Overview of the M'Naghten Rule

The M'Naghten Rule comes from a mid-19th-century English case. There, a man claimed he had a disease of the mind that rendered him not liable for his criminal act. Read on to learn about the M'Naghten case and the development of the M'Naghten Rule in criminal law.

Daniel M'Naghten and Criminal Insanity

Daniel M'Naghten, a British man, suffered from a mental illness that caused him to experience paranoid delusions. He thought the Catholic priests and the Tories conspired against him. The evidence at his criminal trial indicates he believed spies followed him everywhere and intended to kill him.

M'Naghten's plan to stop the alleged persecution was to kill the Tory Prime Minister, Sir Robert Peel. In 1843, he followed a man who had left Peel's house. M'Naghten mistakenly thought the man was Peel. In fact, it was Peel's secretary, Edward Drummond. M'Naghten shot and killed Drummond.

Law enforcement arrested M'Naghten and indicted him for murder. M'Naghten's attorney asserted a defense of insanity at trial. Expert testimony indicated that M'Naghten's delusional thoughts compromised his mental state at the time of the crime. More specifically, his attorney argued that M'Naughten could not distinguish between right and wrong at the time he killed Drummond.

The jury returned a verdict of insanity, and M'Naghten received an acquittal. The Crown institutionalized M'Naghten for the rest of his life.

The M'Naghten Rule

The Queen of England disapproved of the jury's verdict. She asked the English House of Lords to discuss and deliberate insanity defenses. These discussions ultimately led to the M'Naghten Rule, also known as the M'Naghten Test. It states the following:

"Every man is to be presumed to be sane, and ... that to establish a defense on the ground of insanity, it must be clearly proved that, at the time of the committing of the act, the party accused was laboring under such a defect of reason, from disease of mind, and 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."

This test focuses on the following:

  • Whether a criminal defendant knew the nature of the crime
  • Whether they understood right from wrong at the time they committed the crime

Therefore, a defendant must meet one of these two distinct criteria for a court to declare them legally insane.

Courts in the United States adopted the M'Naghten test. In applying this test, courts may differ on whether the wrong refers to a moral wrong, a legal wrong, or both. In addition, some states have eliminated the criteria that define a defendant as legally insane for not fully understanding what they've done.

Examples of Insanity Using the M'Naghten Rule

The best way to better understand this type of legal insanity is to see a few examples of how courts may apply the rule to certain scenarios.

Example 1: A man murdered his family and then waited calmly for the police to arrive. Three mental health experts testified that he was too psychologically ill to understand that his criminal acts were wrong. A jury found him not guilty by reason of insanity and sentenced him to 10 years in a mental health facility.

Example 2: A woman with severe schizophrenia attacked her neighbor with a shovel. The government charged her with assault and battery. She claimed the neighbor was actually a demon who was trying to harvest her soul. A jury found her not guilty by reason of insanity because she did not understand the nature of her actions.

The above examples show the two different ways a court may declare a defendant legally insane under this rule.

Criticism of the M'Naghten Rule

The M'Naghten test for legal insanity has faced several challenges. Some critics argue that defendants meeting the legal definition of insanity don't always meet the medical criteria for insanity. Despite this, courts often sentence them to mandatory medical care.

Other critics say the M'Naghten Rule fails to distinguish between defendants posing a public danger and those who do not. Additionally, some argue it does not differentiate between temporary mental issues and lifelong conditions.

Finally, some argue that the rule makes it too easy for a defendant who has a severe mental disorder to escape responsibility for any crimes.

Other Tests

Courts have used other legal tests to determine whether someone suffering from a mental disease qualifies for the insanity defense.

In 1871, a New Hampshire court rejected the M'Naghten Rule. There, the court determined that someone with a mental illness is not guilty if their crime was a result of their mental illness. Put another way, the defendant would not have committed the crime “but for" their mental illness.

In 1887, the Alabama Supreme Court crafted the Irresistible Impulse Test. There, the court noted that the defendant knew their actions were wrong, but could not control themselves from committing a criminal act. A defendant must show they have a mental illness and the illness caused an inability to control their actions.

In 1954, the United States Court of Appeals for the District of Columbia decided the Durham v. United States case. There, the court created the Durham Rule, which states that "an accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect."

In 1972, the same Court of Appeals set aside the Durham Rule. It replaced it with the Model Penal Code (MPC) of the American Law Institute. The MPC's rule is as follows:

“A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity to appreciate the criminality [wrongfulness] of his conduct or to conform his conduct to the requirements of law."

All federal circuits now use the MPC's rule, and most states use it too.

Learn More About the M'Naghten Rule: Speak to an Attorney

The insanity defense has precise criteria to qualify and can carry lifelong consequences. If you are facing criminal charges and want to know more about the standards of an insanity defense, your first step should be to speak with a knowledgeable attorney. Find out more and speak with a local criminal defense attorney today.

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