R Vs. M’Naghten(1843): Case Brief


The Crown, Plaintiff

M’Naghten, Defendant


In January 1843, in the parish of Saint Martin in Middlesex, Daniel M’Naghten stole a handgun and shot Edward Drummond, whom he mistook for British Prime Minister Robert Pell, gravely wounding him. M’Naghten was charged with Drummond’s murder five days later. He pled not guilty due to insanity. At trial, evidence of the shooting of Drummond was presented, and witnesses were called on behalf of the accused, M’Naghten, to swear to the fact that he was not in a sound state of mind at the time of the crime.

Some of the witnesses who provided this testimony had earlier examined M’Naghten, while others had not seen him before the trial and formed their view based on hearing other witnesses’ arguments. According to the medical information presented, people of an otherwise sound mind can be afflicted by morbid delusions, and M’Naghten was one of them.

A person suffering from such delusion may normally have a moral awareness of good and wrong, but activities related to their hallucination may be carried out beyond their control, leaving them with no such perspective. As a result, M’Naghten was unable to exercise control over his actions while under the influence of his hallucination.

Due to the nature of M’Naghten’s illness, these illusions progressed gradually until they reached a peak, culminating in Drummond’s death. Evidence presented to the Court concerning the condition that M’Naghten experienced showed that a man might carry on for years peacefully while under the grip of the delusion. Still, it could break out into excessive and destructive paroxysms.

M’Naghten was acquitted on all charges. Following that, a panel of Judges appeared before the House of Lords and answered a series of hypothetical questions on insanity.


  1. What is the law regarding alleged crimes committed by people suffering from insane delusions concerning one or more specific subjects or persons, such as were, at the time of the alleged crime, the accused knew he was breaking the law, but did the act complained of under the influence of insane delusions in the hope of resolving or exacting vengeance some supposed wrong?
  2. What are the essential questions to present to the jury when a person accused of having insane delusions about one or more specific things or people is charged with a crime and insanity is raised as a defence?
  3. In what terminology should the jury be asked about the prisoner’s mental state at the time the act was committed?
  4. Is a person pardoned if he commits an offence as a result of an irrational hallucination about existing facts?
  5. Can a medical expert familiar with the disease of insanity, who had never seen the prisoner before the trial but was present throughout the trial and the examination of all witnesses, be asked his opinion as to the state of the prisoner’s mind at the time of the commission of the alleged crime, or his opinion whether the prisoner was conscious at the time of doing the act, that he was committing?

Rule of Law

To establish an insanity defence, it must be clearly demonstrated that, at the time of the act, the accused was suffering from such a defect of reason from a mental disease that he did not know the nature and quality of the act he was committing; or, if he did know, he did not know what he was doing was wrong.


The Judges developed the M’Naghten Rules (1843) 4 St.Tr.(N.S.) 847 in answer to these issues, which provide the legal description of insanity.

Presumption of sanity and burden of proof– The burden of proof is on the side disputing sanity; the standard of proof is on a balance of probability, which means that mental impairment is more probable than not. If this load is effectively fulfilled, the party depending on it has a good chance of succeeding. 

The disease of Mind– Whether a particular illness qualifies as a mental disorder under the principles is a legal matter to be determined in line with ordinary rules of interpretation. It appears that any sickness that causes a malfunction in the mind is a disease of the mind and does not have to be a disease of the brain itself. 

Nature and Quality of the act– This term alludes to the act’s physical character and quality rather than its moral quality. It applies to situations in which the defendant has no idea what he is doing physically. 

The knowledge that the act was wrong– This clause’s meaning is a source of contention among legal authorities, and various standards may apply in different jurisdictions.

Offences of Strict Liability- It was decided that insanity is not a valid defence to strict responsibility offences in general. 

The function of the jury- Section 1 of the Criminal Procedure (Insanity and Unfitness to Plead) Act 1991[17] states that a jury may not return a special verdict that “the accused is not guilty by reason of insanity” unless two or more registered medical practitioners, at least one of whom has unique experience in the field of mental disorder, provide written or oral evidence.

Section 5 of the Criminal Procedure (Insanity) Act of 1964 states that

If the punishment for the offence to which the finding pertains is set by law, the court must issue a hospital order together with a restriction order restricting release and other rights.

In any other situation, the court may issue a hospital order (with or without restrictions), a monitoring order, or an order for unconditional discharge.https://www.lawteacher.net/cases/r-v-m-naghten.php


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