Introduction
The M’Naghten Rules, from M’Naghten’s Case (1843) 10 Cl & Fin 200, form the primary legal test for insanity in many common law jurisdictions. This House of Lords decision defined criteria for deciding if a defendant should be held criminally responsible when they had a "defect of reason, from disease of the mind." The rules focus on the defendant’s ability to think rationally at the time of the offense, particularly whether they understood the act’s physical consequences or knew it was illegal. These standards remain an important part of legal discussions about criminal responsibility related to mental illness.
The Facts of M’Naghten’s Case
Daniel M’Naghten, experiencing paranoid delusions, shot and killed Edward Drummond, secretary to Prime Minister Sir Robert Peel, believing the Tories were targeting him. The jury ruled him not guilty by reason of insanity, causing public discussion and prompting the House of Lords to create a defined legal standard for insanity defenses.
Forming the M’Naghten Rules
Following the verdict, the House of Lords asked judges five questions about the legal test for insanity. The judges’ answers, particularly to the third and fourth questions, established the M’Naghten Rules. These rules focus on the defendant’s mental state during the crime.
The Two Parts of the M’Naghten Test
The M’Naghten Rules have two main requirements:
-
Defect of Reason from Disease of the Mind: The defendant must have had impaired thinking due to a mental health condition. This requires showing a clear loss of reasoning from a medical issue affecting the mind. The condition does not need to be permanent but must have existed during the offense.
-
Understanding the Act or Its Wrongfulness: Because of this defect, the defendant must either not have understood the physical reality of their actions or not recognized their illegality. This part evaluates the defendant’s awareness of their actions and their ability to judge those actions as unlawful.
Defining "Disease of the Mind"
The term "disease of the mind" covers many mental health conditions. Later cases have expanded it to include disorders affecting reasoning, such as schizophrenia, dementia, and epilepsy. It is a legal term, not a medical one, shaped by court rulings. For example, in R v Kemp (1957) 1 QB 399, arteriosclerosis, a physical illness, was considered a "disease of the mind" because it disrupted the defendant’s reasoning. In R v Sullivan [1984] AC 156, epilepsy was also included.
Explaining "Nature and Quality" and "Wrongfulness"
The first part of the second rule—"not knowing the nature and quality of the act"—means the defendant was completely unaware of the physical act. For instance, someone who thinks they are squeezing a lemon but is strangling a person fits this condition. The second part—"not knowing the act was wrong"—means lacking awareness that the act was illegal by societal norms, not personal beliefs. R v Windle [1952] 2 QB 826 highlights this difference.
Criticisms and Changes
The M’Naghten Rules have faced significant debate. Critics argue they focus too much on reasoning defects and ignore issues like uncontrollable impulses. Others say the rules are outdated and do not align with current mental health knowledge. Some areas have adopted alternative tests, such as the Model Penal Code’s substantial capacity test in the U.S., which considers both reasoning and control issues. However, the M’Naghten Rules continue to influence legal discussions on insanity defenses.
The M'Naghten Rules in Legal History
The impact of M'Naghten's Case and its rules extends beyond the trial. It is a core part of legal debates on mental illness and criminal responsibility. Cases like R v Clarke [1972] 1 All ER 219 confirmed that a "defect of reason" requires more than brief confusion. DPP v Beard [1920] AC 479 addressed how to prove insanity. These decisions show how courts still use and interpret the M’Naghten framework.
Conclusion
The M’Naghten Rules, from M’Naghten’s Case (1843), establish criteria for criminal responsibility when insanity is claimed. They require proof of impaired reasoning from a mental health condition, leading to a failure to understand the act’s reality or illegality. While criticized and adapted in some regions, the rules remain an important part of common law systems. Ongoing court interpretations, as seen in R v Kemp, R v Sullivan, R v Windle, and R v Clarke, continue to refine these standards. This decision and later cases demonstrate how the law addresses mental health in criminal cases.
