The Mcnaughten Rule

Last Updated: 28 Jan 2021
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The M’Naghten Rule: 1843 Aspects of the Criminal law in Canada are likely to be traced back several hundred years ago, where the legal system was established in England. Criminal law, derived from public law, includes the subject of criminal defenses, and in a narrower sense, the theory of not being criminally responsible on account of a mental disorder. The theory behind this defense can be traced back to England in the 1840’s. This era showcased the influential case of Daniel M’Nagthen.

Believed to be a paranoid schizophrenic, M’Naghten shot and killed Edward Drummond, Secretary to the British Prime Minister, Sir Robert Peel. M’Naghten was under the delusion that he was being persecuted by Peel who was at the time a strong advocate of the police enforcement system. The case states that Daniel M’Naghten, had shot the Secretary, Edward Drummond, thinking he was Peel and was put on trial for the murder of Edward Drummond. As this stood, M’Naghten pleaded not guilty on the statement that he was mentally ill and having delusions, which had influenced his action to murder Drummond.

The court system of England pronounced M’Naghten as not guilty by reason of insanity. The case gave way to the now titled M’Naghten rule claiming that an individual cannot be found guilty on the grounds that he or she is unable to tell the difference between right and wrong (Siegle, McCormick 2010). The M’Naghten rule has set a foundation of defining criminal responsibility and allowed for the introduction of mental disorders and psychological conditions as being able to influence whether or not an individual can be held criminally accountable.

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There was great public outcry on this verdict which forced the House of Lords to amend the standards for the defense of insanity and resulted in the rule that states: “ every man is to be presumed sane, and that to establish a defense on the grounds 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, 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 (8 Eng. Rep. 718 (1843))”.

Criticism for the M’Naghten rule arose because it tended to rely entirely on the defendant’s cognitive ability to “know” right from wrong. Subsequently, there are also questions about what to do with defendants who can differentiate the wrongfulness they committed but can’t control the impulses to commit them. Combined, these factors either emotional or cognitive can make it difficult for defendants to be found not guilty by reason of insanity. Despite the criticisms, the M’Naghten Rule is still widely applied today in both the Canadian and United States legal system.

Evolving a greater understanding of applying the “insanity defense” leads the way to other methods and theories for understanding and defining mental insanity. Looking into the Biological Trait Theory asks the question as to whether or not individuals can be “born criminal” (Garofalo, 178). It is known that mental disorders are almost, always genetically based, however diagnosing someone, as having a mental disorder, does not define them as a criminal. This is where behaviour and personality characteristics come into play, indicating a criminal nature.

Many biological factors, such as body weight and height are incorporated into creating a stereotype of a criminal, a method called somatyping. It is important to take into account the lifestyle of the accused. Many factors such as the home structure, daily routine, nature and nurturing, education, friends, interest all play an impactful role in either noticing an onset of a mental disorder to noticing the beginning of criminal behavior. Some of these characteristics can come into play as well in the Psychological Trait Theory, focusing on the mental aspect of crime.

From a psychodynamic perspective, there are two classifications to describe mental disorder, in individuals who struggle with mental anguish and loss of control of their personality. This can manifest in an individual who experiences neurosis or psychosis. Neurosis is described as being on the borderline between reality and the sense of losing control of your personality, and psychosis is the loss of total control leaving them detached from reality. Psychotic behavior is often marked by bizarre episodes of delusion or hallucinations. It can take on many forms, the most common being Schizophrenia.

In a broad sense, the person is left with complete loss of thought control or appropriate emotional responses. They can become paranoid, delusional, hallucinate or withdraw completely from reality. As in the M’Naghten case of 1843, Daniel M’Naghten was thought to be a paranoid schizophrenic, which caused or provoked his violent reaction toward Edward Drummond. Due to the many theories and perspectives about the rooting and origins of mental disorders, it is no wonder why there is such a high correlation between crime and mental illness.

Many characteristics of mental illness are also very similar to those categorized as being criminal in nature. The authors of “Clinical predictions of Self-Mutilation in hospitalized patients” stated that mentally ill individuals are more likely to withdraw or harm themselves than to act aggressively towards others (1994), which begins to ask the question if mentally ill individuals are more criminal than those who are not mentally ill. And, do you have to be mentally ill to commit a crime.

This is why criminal cases involving mental illness are hard to defend or hard to prosecute. There does not seem to be a simple direct way to interpret the complete science of these theories. In conclusion, criminal behavior as it relates to understanding the relationship to mental illness is an evolving behavioral science. Nearly 170 years after the M’Naghten Rule was established the legal system in North America is still struggling to find the balance at defining mental insanity.

There is significant research to establish that people can be born into crime based on their genetics or the environment and that psychotic behavior can lead to irrational thoughts and feelings that provoke people to do terrible things. The question still exists as to whether individuals from any of these perspectives actually understand if they had intent to commit a crime or understand completely that what they did was wrong.

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The Mcnaughten Rule. (2018, Jul 24). Retrieved from

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