Insanity — M'Naghten's Case

Facts

Daniel McNaghten shot and killed Edward Drummond, the secretary of the Prime Minister, Sir Robert Peel, having mistaken him for the Prime Minister. McNaghten laboured under delusions that he was being persecuted by the Government and that this justified his act.

History

McNaghten was tried for murder and was found not guilty on the ground of insanity. The verdict caused public concern and, following debate in the House of Lords, the fifteen judges of the common law courts were asked a series of questions on the law relating to crimes committed by persons with insane delusions. Their answers were delivered to the House in 1843.

Issue

What the law of criminal responsibility is where a person commits an offence while suffering from an insane delusion, and what direction should be given to a jury when the defence of insanity is raised.

Held

The judges advised that every person is presumed sane until the contrary is proved, and that to establish a defence on the ground of insanity it must be clearly proved that, at the time of the act, the accused was labouring 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 that what he was doing was wrong.

Ratio

• The accused is presumed sane and the burden of proving insanity lies on the defence; the defence is established if, at the time of committing the act, the accused was labouring under a defect of reason from disease of the mind, so that he did not know the nature and quality of the act or did not know that it was wrong.
• A person suffering from a partial delusion is to be treated as though the facts with respect to which the delusion exists were real, and is not exempt from responsibility if, on those facts, he would have been liable.

The judgments

Key reasoning

• The judges treated criminal responsibility as resting on the capacity of the accused to understand what he was doing and to know that it was wrong, so that a defect of reason falling short of that was no defence.
• On delusions, the judges held that the accused is to be judged as if the facts he imagined were true, so that a person who killed under a delusion that he was acting in self-defence would be excused only if that would be a defence if true.
• The answers dealt with the question whether the accused knew the act was wrong in the legal sense, and with the use of expert medical evidence on the state of mind of the accused.

Where it fits in the module

In the Incapacity and General Defences topic the rules form the starting point for the law of insanity and its relationship with automatism, intoxication and diminished responsibility. They are read in the debate over whether a legal test based on cognition is consistent with modern psychiatry and how mental disorder should affect responsibility.

Criticisms

• The test is based on cognition alone, so it excludes defendants who knew what they were doing and that it was wrong but whose illness deprived them of the ability to control their conduct.
• The rules rest on an outdated medical understanding of mental illness and require the medical evidence to be fitted into narrow legal categories that do not match diagnosis.
• The label of insanity and the outcome of a special verdict is stigmatising, and the broad meaning given to disease of the mind in later cases on diabetic and sleepwalking defendants has led to results that many regard as inappropriate.