The case of M'Naghten (1843) established the defence of insanity. M'naghten, pictured on the left, was attempting to assassinate the then Prime Minister, Sir Robert Peel. He missed and killed Peel's secretary, Edward Drummond. Medical opinion indicated that the defendant was mentally ill. The House of Lords set out three key issues that must be established for the defence of insanity to succeed.
These key issues are:
1. defect of reason
2. caused by disease of the mind
3. so that the defendant does not know the nature and quality of his act or does not know that what he was doing was wrong.
What do we mean by 'defect of reason'?
'Defect of reason' does not mean a person is confused or absent minded. According to the law, defect of reason means that the defendant was unable to use his powers of reason at the time of the offence. This is different to a defendant failing to use his powers of reason.
Let's look at the case of Clarke (1972) to better understand the difference between a defendant failing to use their power or reason, versus a defendant who is unable to use their power of reason.
Facts: The defendant was charged with stealing from a supermarket. She had put some items in her basket, and left the shop without paying.
The defendant said she had no intention to steal. She claimed that in a moment of absent-mindedness, she put the items in her bag.
This absent-mindedness, it was argued, was caused by her domestic problems, clinical depression and diabetes.
On appeal, the court said at the time of the theft, she was not 'deprived of reason'. She was temporarily absent-minded. She had failed to use her powers of reason, but she was not 'unable' to use it.
What is meant by caused by 'disease of the mind'?
The medical definition of 'disease of the mind' is different to the legal definition. The legal meaning of the term has developed through case law. The main principles that the court developed are that the disease of the mind must not be caused by external factors such as drugs, it must be a physical disease ; and it can be a permanent or a temporary state.
Let's look at the following cases to understand these principles better.
Facts: The defendant suffered from arteriosclerosis which affected blood flow to his brain. This sometimes resulted in temporary lack of consciousness. On one occasion, he attacked his wife with a hammer and killed her.
The court established that a disease of the mind could be temporary and the actual medical condition of the brain was, in itself, irrelevant.
Facts: The defendant strangled a girl while he was suffering from a psychomotor epileptic seizure. This type of seizure causes sufferers to carry out purposeful acts whilst in an unconscious state. The defendant removed the victim's tights and strangled her with them.
The court stated that this type of seizure could amount to insanity.
Facts: During an epileptic fit, the defendant kicked and injured his neighbour.
The court concluded that the fact the minor epileptic fit was temporary did not prevent it from being a disease of the mind.
Facts: The defendant hit his friend across her head with a bottle and a video recorder and then grabbed her by the throat. She then screamed. He realised what he had done and said he had been sleepwalking. He was charged with s 18 Offences Against the Person Act 1861.
The court concluded that the sleepwalking was caused by an internal factor, it was therefore a disease of the mind.
Did the defendant know the nature and quality of this act? Did they know that what he was doing was wrong?
Facts: The defendant killed his insane wife. When he had handed himself into the police he had said 'I suppose I'll hang for this.' In court he pleaded the defence of insanity.
The court denied the defence of insanity. They concluded that his statement 'I suppose I'll hang for this' indicated he knew the nature and quality of his act- and that he knew that what he was doing was wrong. He was convicted for murder.