Insanity And The M’Naghten Rule: How Crazy Is “Crazy”?

Legal Background

In 1843, in England, Daniel M’Naghten, who some say was paranoid schizophrenic, suffering with a delusion of being persecuted, killed the secretary to the prime minister. To the public’s great surprise, the court found him insane and not guilty of the crime. The British parliament was convinced by public outrage to establish a new insanity standard for homicide, now known as the M’Naghten Rule, which provided as follows: “[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.”

While many states no longer use the M’Naghten Rule, or have supplemented it with other insanity defenses, Minnesota continues to use the rule as its sole insanity defense, with the burden of proof being placed on the defendant. As stated in the Minnesota statutes: “No person having a mental illness or cognitive impairment so as to be incapable of understanding the proceedings or making a defense shall be tried, sentenced or punished for any crime; but the person shall not be excused from criminal liability except upon proof that at the time of committing the alleged criminal act, the person was laboring under such a defect of reason, from one of these causes, as not to know the nature of the act, or that it was wrong.”

History Of The Rule

Over the years, many attempts have been made to amend or repeal the law. As of late 2010, the National Alliance on Mental Illness stated: “The standard for the ‘insanity defense’ … is based on outdated notions of mental illness[.] NAMI favors changing the standard to ‘the person did not know or substantially appreciate the nature of the act or its legal or moral wrongfulness.” None of these efforts have proven successful.

While the news media publicizes criminal cases in which the defendant pleads not guilty by reason of insanity, and while many people are critical of the defense, voicing the opinion that just because you’re “crazy,” you should not “get away with murder,” recent studies demonstrate that such a defense is utilized in fewer than 1% of cases, being successful in about one-fourth of those cases.

Successful Use Of The Rule

Despite the above statistics, there have been cases in which the M’Naghten Rule has been used successfully. In one case, in 2010, a man who killed his stepmother by decapitating her was found not guilty, when the defense and the prosecution both agreed that the defendant was mentally ill, preventing him from knowing right from wrong. The facts of the case showed a long history of mental illness, including a diagnosis of schizophrenia.

At the time of the crime, according to, he said: “It was like I was watching me do it[.] She might have been surprised[.] I don’t think her head had ever been separated from her body before.” The defendant was committed to Minnesota Security Hospital.


For those charged with homicide, insanity as defined by the M’Naghten Rule remains a legitimate defense (if seldom used successfully). If you, or a loved one, ever find yourself charged with homicide, you should immediately contact an experienced homicide attorney to investigate the facts and to provide you with the defense that is best suited to your situation.

Practice Areas

  • Criminal Defense 100% 100%
  • Family Law 100% 100%
  • Child Protection 100% 100%
  • Maltreatment 100% 100%
  • Professional Licensure 100% 100%
  • Tax Law 100% 100%
  • Appeals 100% 100%
  • Wills 100% 100%

Why Hire Us?

At Groshek Law PA, each client is viewed as an individual, not a legal problem.


We start with a proactive approach through mutual education.


We expect the unexpected, so we are always prepared.


Our attorneys adhere to the Highest Professional Standard.