A defence in criminal law arises when conditions exist to negate specific elements of the crime: the actus reus when actions are involuntary, the mens rea when the defendant is unaware of the significance of their conduct, or both. These defences will mitigate or eliminate liability from a criminal offence. Insanity, automatism and diminished responsibility are examples of said defences. They each share characteristics but can be distinguished in their scope and application.
Insanity, automatism and diminished responsibility all play a significant role in cases where the defendant’s mind is abnormal while committing a crime. The definition of abnormal will be reviewed in relationship to each defence. In order to
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When there is a defect of cognitive awareness, it may operate to negate the actus reus and mens rea of the crime. Furthermore, the nature of the disease of mind is irrelevant provided that the mental faculties of reason, memory and understanding are impaired at the time of the offence. In a case where the defendant is aware of the nature and quality of his offence, insanity may still be a valid defence if he does not know his action was wrong. In R v Windle, the defendant demonstrated that his conduct was contrary to law, therefore illustrating his knowledge that his act was wrong. Automatism shares commonalities and differences with insanity in relation to its definition and when it will succeed as a defence.
Automatism, as defined by Lord Denning in Bratty v A-G for Northern Ireland, is an involuntary act which means “an act which is done by the muscles without any control by the mind such as spasm, a reflex or a convulsion; or an act done by a person who is not conscious of what he is doing, such as an act done whilst suffering from concussion, or whilst sleepwalking.” Automatism can have a physical or mental cause and the defence can result from a lack of actus reus and/or mens rea, but can also be a valid defence for crimes of negligence and strict liability. Effectively, automatism has three requirements: complete loss of control,