Daniel M’Naghten: The Man Who Changed the Law on Insanity

Psychiatric TimesVol 40, Issue 1

"Despite many unanswered questions, Daniel M’Naghten is forever remembered as the man who set a lasting legal precedent."



Those trained in psychiatry should be familiar with the M’Naghten (pronounced McNaughton) Rule, which states that:

  1. an individual suffers from a “defect of reason,” which is
  2. caused by a “disease of the mind,” and, as a result,
  3. does not know the “nature and quality” of the act or that it was wrong.1

The rule arose after Daniel M’Naghten shot Edward Drummond, private secretary to British Prime Minister Sir Robert Peel, in mistake for Peel. The trial set a precedent in British law and related jurisdictions that has been followed ever since. Although the rule is well known, few know much about the man who was to have such influence on the law of insanity.

To start with, there is the issue of his name: It is arguably the most misspelled name in legal history. Although often spelled as McNaughton, despite recurrent corrections, the world still knows it as M’Naghten.2 For that reason, we will use it here.

Daniel M’Naghten was born in Glasgow, Scotland, around 1814. After the death of his mother, M’Naghten became a journeyman at the family workshop. After a 3-year career as an actor, he returned to Glasgow in 1835 and set up his own woodturning workshop.3

Despite his lack of formal education, M’Naghten was assiduous in studying acting, reading philosophy, and learning French. He moved in radical circles and was involved in the Chartist movement.3 At one stage, he attended anatomy lectures at Edinburgh Medical School where, according to a conspiracy theory, he learned to feign madness.2

By the time he was 30 years old, M’Naghten was plagued by intrusive paranoid thoughts about police and church officials. A fixation about the ruling Tory party led him to believe that he had been singled out for persecution after he voted against their candidate in an election.

In 1841, M’Naghten went to London and France but complained that the people were persecuting him. Returning to Glasgow, he purchased 2 pistols, telling his landlady that they were for shooting birds.

In 1842, M’Naghten traveled to London and spent several weeks lurking around Westminster and Whitehall. Spotted by a Metropolitan Police Constable Silver, he was described as a “seedy-looking person, height about 5-feet-6, who frequents the Houses of Parliament to solicit conservative members.”

On the afternoon of January 20, 1843, M’Naghten stalked a figure walking along Whitehall toward Downing Street. The target in his sights was Drummond, Peel’s private secretary. M’Naghten caught up with him and shot him at point-blank range in the back near Horse Guards Parade, believing he had assassinated the prime minister.

Drummond seemed to have escaped serious injury and was able to walk home to receive medical attention. However, complications set in, and he died after 5 days.

M’Naghten, making no effort to escape, was immediately arrested. His statement to the police gives some insight into his state of mind:

“The Tories in my native city have compelled me to do this. They follow and persecute me wherever I go and have entirely destroyed my peace of mind. They followed me to France, into Scotland, and all over England; in fact, they follow me wherever I go. I cannot sleep nor get no rest from them…. I believe they have driven me into a consumption. I am sure I shall never be the man I was. I used to have good health and strength, but I have not now. They have accused me of crimes of which I am not guilty; in fact, they wish to murder me. It can be proved by evidence. That’s all I have to say.”

The police found a bank receipt for £750 (equivalent to $53,000 today) on M’Naghten. The funds enabled M’Naghten’s father to organize a team of lawyers and doctors to defend him.

The matter proceeded to trial at the Central Criminal Court of England and Wales, or the Old Bailey, on March 2 and 3, 1843, before Lord Chief Justice Tindal, Justice Williams, and Justice Coleridge. While being prosecuted by the solicitor-general, Sir William Webb Follett, M’Naghten had excellent representation led by the prominent barrister Sir Alexander Cockburn.4

Charged with the “wilful murder of Mr. Drummond,” M’Naghten responded, “I was driven to desperation by persecution.” When asked to clarify, he said, “I am guilty of firing,” which was taken as a not guilty plea.5

Although both sides agreed that M’Naghten suffered from delusions of persecution, the prosecution argued that he was only insane on the subject of politics, and, unless he was proved to be generally incapable of knowing “right from wrong,” was legally responsible for his crime.3

M’Naghten’s defense was that his mind was normal in every way aside from the delusion he carried. Medical witnesses called by the defense included Dr Edward Thomas Monro, Sir Alexander Morison, and Dr Forbes Winslow, who testified that M’Naghten’s delusions had deprived him of “all restraint over his actions.” M’Naghten was lucid in his presentation; he was able to save a sizable amount of money; he had never been institutionalized.

“A fierce and fearful delusion” caused a breakdown of moral sense and loss of self-control, which left him in a state in which he was no longer a “reasonable and responsible being.”

M’Naghten’s behavior was a form of monomania—an insane fixation upon a particular issue, subject, or person. The effect of his delusions had eradicated his ability to tell right from wrong.6

Citing Isaac Ray, author of A Treatise on the Medical Jurisprudence of Insanity (1838), M’Naghten’s lawyers argued that the law should recognize partial insanity as a defense to murder.7 The soundness of his mind in other aspects of his life was irrelevant; if he had been acting under the force of his delusions at the time of the killing, then he must be considered insane. To shoot Drummond in broad daylight in front of witnesses on one of London’s busiest streets, then wait for arrest, was hardly the modus operandi of a calculated killer.

The 2 Crown doctors also found him insane and were not asked to testify. Solicitor-General Follet then withdrew with the words, “I cannot press for a verdict against the prisoner.”

Lord Chief Justice Tindal, summing up, stressed that the medical evidence was all on 1 side. The jury found that M’Naghten should be considered insane due to monomania and was therefore not guilty of murder—that is, not guilty by reason of insanity.

In his book Knowing Right from Wrong: The Insanity Defense of Daniel McNaughtan, Richard Moran considered the possibility that the verdict may have owed as much to political expediency as to mental illness, influenced by the attempted murder of 9 other individuals in the north of England.3

The acquittal caused an uproar.7 If M’Naghten could successfully claim to be insane, then what protection did society have? No less than Queen Victoria—whose own assailant, Edward Oxford, had been found insane in 1840—expressed her dismay over the finding.

So great was the controversy that the House of Lords requested that the judges of the Supreme Court of Judicature answer 5 questions regarding the culpability of the insane and the use of insanity as a defense in a criminal trial. As there was no recognition of temporary or partial insanity in English law, it had to be decided whether M’Naghten should still be considered insane and therefore not guilty of murder.

The Judicial Lords decided that M’Naghten was not guilty, nor could others be, provided the accused met a special threshold. The presumption was that every defendant is sane; but this could be rebutted if the defendant could prove their insanity. To do so, they had to satisfy the following test: to clearly prove that, at the time of committing of the act, the party accused was laboring under such a defect of reason, from disease of the 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

The new rules, formulated as M’Naghten’s Case 1843 10 C & F 20,9 built on the definition of insanity applied in John Bellingham’s case back in 1812, which was only concerned with whether Bellingham knew that his murder of the British Prime Minister Spencer Perceval was a crime and did not include any reference to mental illness.10

In essence, the “M’Naghten Rules” boil down to 4 essential points that a defendant must prove in order to satisfy the court that they are not responsible for the consequences of their actions. First, the defendant must establish an underlying medical condition (“disease of the mind”), and second, prove that this condition has caused an impact on their mental processes and understanding (“defect of reason”).

If the court is satisfied with both of these, that leaves 2 further hurdles to clear to succeed with an insanity plea: Either the defendant did not understand what they were doing at the time of the criminal act (“nature and quality of the act”), or, if they were aware of what they were physically doing, they did not realize that the act was prohibited (“doing what was wrong”).

The jurors must be told in all cases that every individual is to be presumed to be sane and to possess a sufficient degree of reason to be responsible for their crimes, until the contrary be proved to the jury’s satisfaction. A sufferer could be rational and coherent—sane for all intents and purposes—on any subject other than their specific fixation, over which they had little to no control.

The M’Naghten Rules still apply today in English courts, Commonwealth countries, and countries such as the United States, Hong Kong, India, the Republic of Ireland, and Norway, although some jurisdictions have their own variants of the rule.

Paradoxically, despite setting such an important legal precedent, M’Naghten was never judged against the rules that bear his name. He was ordered to be held indefinitely at Bethlem Royal Hospital, at St George’s Fields, Southwark.11 The admission notes list his single status, Episcopalian religion, jury verdict “guilty but insane,” crime of murder, and sentence, “at Her Majesty’s Pleasure.” He spent the next 21 years confined in a stone cell measuring 8.5 by 10.5 feet.

In 1864, M’Naghten was transferred to the new Broadmoor Criminal Lunatic Asylum in Berkshire,12 established as an institution for “criminal lunatics” (ie, those detained under Her Majesty’s Pleasure following an insanity acquittal at a criminal trial).13

M’Naghten’s admission notes state that he was “a native of Glasgow, an intelligent man, [who] states that he must have done something very bad or they would not have sent him to Bethlehem [Bethlem Hospital].”

The notes also directly give the sentence of the Lord Chief Justice: “Acquitted on the grounds of insanity, to be confined at Her Majesty’s Pleasure. When asked whether he now thinks he must have been out of his mind, he replies, ‘Such was the verdict—the opinion of the jury on hearing of the evidence.’”

At 1:10 AM on May 3, 1865, aged 52 years, M’Naghten died from renal and heart disease, leaving many questions unanswered. However, Daniel M’Naghten is forever remembered as the man who set a lasting legal precedent.13

Dr Kaplan is a forensic psychiatrist in the School of Medicine at Western Sydney University, Australia, and a research fellow in the Department of History at Stellenbosch University, South Africa. His latest book The King Who Strangled His Psychiatrist and Other Dark Tales is seeking a publisher.


1. Kaplan J, Weisberg R, Binder G. Criminal Law: Cases and Materials. 7th ed. Wolters Kluwer Law & Business; 2012.

2. Dalby JT. The case of Daniel McNaughton: let’s get the story straight. Am J Forensic Psychiatry. 2006;27(4):17-32.

3. Moran R. Knowing Right From Wrong: The Insanity Defense of Daniel McNaughtan. The Free Press; 1981.

4. Walk A, West DJ, eds. Daniel McNaughton: His Trial and the Aftermath. Gaskell Books/Royal College of Psychiatrists; 1977.

5. State Trials Report: The Queen v Daniel McNaughton, 1843. Reprinted in Walk A, West DJ. Daniel McNaughton: His Trial and the Aftermath. Gaskell Books//Royal College of Psychiatrists; 1977.

6. Shorter E. A Historical Dictionary of Psychiatry. Oxford University Press; 2005.

7. Diamond BL. Isaac Ray and the trial of Daniel M’NaghtenAm J Psychiatry. 1956;112(8):651-656.

8. M’Naghten’s case. Justia. Accessed December 23, 2021. https://law.justia.com/cases/foreign/united-kingdom/8-eng-rep-718.html

9. United Kingdom House of Lords decisions: Daniel M’Naghten’s case. British and Irish Legal Information Institute. Accessed December 23, 2021. https://www.bailii.org/uk/cases/UKHL/1843/J16.html

10. Goddard KS. A case of injustice? the trial of John Bellingham. Am J Leg Hist. 2004;46(1):1-25.

11. Allderidge P. Why was McNaughton sent to Bethlem? In: West DJ, Walk A, eds. Daniel McNaughton: His Trial and the Aftermath. Gaskell Books/Royal College of Psychiatrists; 1977:100-112.

12. Broadmoor Hospital. Historic England. Accessed December 19, 2021. https://historicengland.org.uk/listing/the-list/list-entry/1001401

13. Morgan K. Murder: The Biography. Mudlark; 2021.

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