M’Naghten’s Case [1843] UKHL J16; (1843) 10 Cl & F 200; 8 ER 718
Insanity; knowledge of the act and its wrongfulness; delusions; medical opinion evidence.
After Daniel M’Naghten was acquitted of murder on the ground of insanity, the House of Lords asked the judges to explain the applicable law. Their answers set out the principles known as the M’Naghten rules. These were responses to general questions, not an appeal overturning or affirming his acquittal.
Trial and background
M’Naghten shot Edward Drummond in January 1843. Drummond died from the wound, and M’Naghten was tried for murder at the Central Criminal Court.
Medical witnesses described him as suffering from delusions. Their evidence was that, although a person with such delusions might ordinarily distinguish right from wrong, M’Naghten’s condition deprived him of that perception and control in relation to acts connected with his delusions. Some witnesses had examined him beforehand; others formed their opinions after hearing the evidence at trial.
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Chief Justice Tindal directed the jury to consider M’Naghten’s understanding at the time of the act, including whether he knew that he was doing something wrong. The jury returned a verdict of not guilty on the ground of insanity.
The verdict prompted debate in the House of Lords. On 19 June 1843 the judges answered five questions concerning delusions, the proper directions to a jury, and the use of medical opinion evidence.
The principal test
Tindal gave the collective answer of the judges other than Maule J, who answered separately. They stated that a person was presumed sane and responsible until the contrary was proved to the jury’s satisfaction.
To establish the defence, it had to be clearly proved that, at the time of the act, the accused suffered a defect of reason caused by disease of the mind, with either of two consequences:
- the accused did not know the nature and quality of the act; or
- although knowing its nature and quality, the accused did not know that the act was wrong.
The inquiry concerned the particular act charged, rather than an abstract ability to distinguish right from wrong. The judges also warned against wording which might suggest that the prosecution had to prove actual knowledge of the law. Their answer stated that a person conscious that the act was one they ought not to do was punishable if it was also contrary to law.
The answers concerning delusions
The judges did not treat every delusion as an excuse. Answering the first question on the assumption of a partial delusion without insanity in other respects, they said that a person who knew the act was contrary to law remained punishable even if the delusion led them to believe they were redressing a grievance or producing a public benefit.
For the fourth question, on the same assumption, responsibility depended on how the act would be treated if the facts imagined under the delusion were real. The judges contrasted killing in supposed self-defence against an immediate threat to life with killing in revenge for an imagined injury to reputation or fortune. The former could excuse the person; the latter would not.
Medical evidence and the jury’s role
The final question concerned a medical witness who had not previously examined the accused but had heard the trial evidence. The collective answer distinguished expert scientific opinion from deciding whether disputed factual evidence was true, which was the jury’s task. A general question about the accused’s mental state could improperly require the expert to decide those disputed facts.
Where the facts were admitted or undisputed, however, the issue could become substantially scientific, and allowing the question in that form might be convenient. Maule J placed greater emphasis on the established practice of receiving such evidence, including at M’Naghten’s trial.
Scope of the answers
The stated test centred on the accused’s knowledge of the act and its wrongfulness. The medical evidence about loss of control at the trial did not become a separate rule that an inability to resist an impulse automatically established the defence.
Maule J also cautioned against answering wide questions without particular facts or argument from counsel. The other judges acknowledged the difficulty of applying general answers to the varied circumstances of individual cases.
Original report: M’Naghten’s Case, including the trial account and the judges’ answers of 19 June 1843.
