Facts
- Daniel M’Naghten, experiencing paranoid delusions, fatally shot Edward Drummond, private secretary to Prime Minister Sir Robert Peel, believing political enemies pursued him.
- A jury returned a verdict of not guilty by reason of insanity.
- Widespread public concern led the House of Lords to seek guidance from the common law judges, submitting five questions on the scope of the insanity defence.
Issues
- What legal test should govern criminal responsibility when insanity is pleaded?
- How should “disease of the mind” and the resulting “defect of reason” be defined?
- Must the mental disorder render the accused unaware of the act’s nature and quality, or of its wrongfulness, to warrant acquittal?
Decision
- The judges’ responses crystallised into the M’Naghten Rules.
- An accused is excused only if, at the time of the act, he was labouring under a defect of reason caused by a disease of the mind.
- Because of that defect he must either (a) not know the nature and quality of the act, or (b) know the act but not that it was wrong.
- The Rules focus on cognitive impairment; an irresistible impulse alone does not suffice.
Legal Principles
- “Disease of the mind” is a legal concept encompassing disorders that impair reasoning, later applied to conditions such as arteriosclerosis (R v Kemp) and epilepsy (R v Sullivan).
- “Defect of reason” demands more than transient confusion; brief absent-mindedness, as in R v Clarke, is insufficient.
- Ignorance of “nature and quality” concerns physical awareness of the act (e.g., mistaking strangulation for squeezing a lemon); ignorance of wrongfulness relates to legal knowledge, illustrated by R v Windle.
- The Rules remain the common-law standard, applied in cases like DPP v Beard, though criticised for their exclusive cognitive focus and limited concordance with modern psychiatry.
Conclusion
The House of Lords established the two-limb M’Naghten test, excusing only those whose disease-based defect of reason left them unaware of the act’s nature, quality, or legal wrongfulness; this framework endures as the core common-law standard for insanity despite sustained criticism.
