Insanity and automatism

Insanity and automatism are best understood as doctrines of criminal incapacity. They do not deny that the prohibited harm occurred. They ask whether the defendant’s bodily movement or mental functioning was such that ordinary attribution of criminal responsibility is unsafe. Week 13 therefore connects directly with Week 1 on actus reus and Week 2 on mens rea, but it also tests a deeper question: when is a person properly answerable for conduct which, in a physical sense, came from his body?

The law draws a sharp and often artificial line between insanity and automatism. Insanity is governed by the M'Naghten rules. If the defendant, owing to a disease of the mind, suffered such a defect of reason that he did not know the nature and quality of his act, or did not know that what he was doing was wrong, the special verdict is not guilty by reason of insanity. Automatism is a common law doctrine of involuntariness. If the defendant acted in a state of total loss of voluntary control caused by an external factor, there is no actus reus in the ordinary sense and, usually, an ordinary acquittal follows.

The practical significance of the distinction is considerable. Insanity carries a special verdict and a range of disposals, potentially including hospitalisation. Non-insane automatism is a complete acquittal. Yet the line between the two is not drawn by medical classification. Epilepsy, sleepwalking, arteriosclerosis and hyperglycaemia have been treated as insanity; hypoglycaemia caused by insulin, concussion, anaesthetic reaction, and some shock-induced states have been treated as possible automatism. The law’s concern is not whether psychiatrists would call the condition insanity. It is whether the cause is internal, recurrent, and dangerous in a way that justifies the special verdict.

For Durham Criminal Law, this topic is a high-value examination topic because it rewards precise legal taxonomy. A good answer must not collapse insanity, automatism, intoxication, mistake, diminished responsibility and unfitness to plead. You have already studied intoxication in Week 12: remember that self-induced intoxication will rarely assist and may defeat a plea of automatism. You have also studied diminished responsibility in Week 4: that is a partial defence to murder only, requiring abnormality of mental functioning under the Homicide Act 1957 as amended, and it does not replace insanity. Insanity applies across offences, though it is awkward where the offence is one of strict liability. Automatism, by contrast, is a denial of voluntary conduct.

The central exam skill is sequencing. First ask whether there was voluntary conduct. If not, ask whether the involuntariness was caused by an external factor, in which case non-insane automatism may arise, or by an internal condition amounting to a disease of the mind, in which case insanity is the proper route. Then consider whether the defendant’s control was totally destroyed; partial impairment is insufficient for automatism. Finally, for insanity, test each element of M'Naghten: disease of the mind, defect of reason, and lack of knowledge of the nature and quality of the act or that the act was legally wrong.

The modern law of insanity begins with Daniel M'Naghten. In 1843 M'Naghten, apparently suffering from delusions of persecution, shot and killed Edward Drummond, the private secretary of Sir Robert Peel. His acquittal on the ground of insanity provoked political and public controversy. The House of Lords then posed questions to the judges, producing what are still called the M'Naghten rules. The rules were not enacted as a code. They were judicial answers to parliamentary questions. Yet they became the foundation of English insanity doctrine.

The historical form of the doctrine matters. The M'Naghten rules were framed in cognitive terms. They focus on the defendant’s knowledge: did he know the nature and quality of the act, and did he know that what he was doing was wrong? They do not contain an independent volitional limb for irresistible impulse. A defendant who understands what he is doing and knows it is wrong, but says he could not resist, is not within the classic rules. That omission has long been criticised, particularly where mental disorder impairs control rather than cognition. Diminished responsibility, introduced much later for murder, partly alleviates this problem in homicide, but does not solve it for other offences.

The nineteenth-century insanity doctrine also reflected institutional assumptions about confinement. The old special verdict was that the accused was guilty but insane. The Criminal Procedure (Insanity) Act 1964 changed the formulation to not guilty by reason of insanity. That linguistic shift matters. It recognises that the defendant is not being convicted. But the social meaning of the verdict remains ambivalent: it is an acquittal with possible compulsory measures.

Automatism developed more explicitly from the actus reus requirement. If criminal liability ordinarily requires a voluntary act, a movement performed by the body without control by the mind should not be punishable. The common examples are concussion, spasms, reflex actions, and states of unconsciousness. However, once the courts accepted that some conditions producing involuntary behaviour are internally generated, they placed those cases within insanity. This has created the doctrinal tension which dominates the modern law.

The leading mid-twentieth-century cases show a movement away from lay insanity toward a broader legal concept. In Kemp, arteriosclerosis causing a temporary black-out was a disease of the mind. In Sullivan, epilepsy was a disease of the mind. In Burgess, sleepwalking with violent conduct was treated as insanity. These decisions make sense if the law is concerned with public protection and recurrence. They make less sense if insanity is supposed to track psychiatric illness or moral blameworthiness.

A further historical strand is the law’s suspicion of self-induced incapacity. That theme was developed in intoxication, but it also affects automatism. If the defendant knows that taking insulin without eating, taking drugs, or engaging in risky conduct may cause loss of control, the law may deny a full automatism defence or treat the case through fault at the point of becoming impaired. The law therefore combines three different ideas: absence of voluntary act, mental disorder, and prior fault. Their coexistence explains both the fascination and the instability of the subject.

The first principle is that insanity is a legal, not medical, concept. A condition may amount to insanity even if no psychiatrist would describe the defendant as insane. Conversely, a recognised psychiatric disorder will not assist unless the M'Naghten elements are satisfied. The phrase disease of the mind means a disease affecting the functioning of the mind, not necessarily a disease of the brain. The courts have treated arteriosclerosis, epilepsy and sleepwalking as diseases of the mind. The central question is whether the impairment arises from an internal condition of the defendant, especially one carrying a risk of recurrence.

The second principle is that M'Naghten requires a defect of reason. This means more than absent-mindedness, confusion, stupidity or failure to use available reasoning powers. The defendant’s reasoning must be impaired by the disease of the mind. Mere intoxication is not itself insanity. A defendant who is angry, impulsive, morally depraved, or unwilling to think is not suffering from a defect of reason merely because his decision-making was poor. In an exam problem, identify the medical or psychological condition, then ask whether it actually impaired the defendant’s capacity to reason at the material time.

The third principle concerns the two cognitive limbs. The defendant may be insane if he did not know the nature and quality of the act. This refers to the physical character and consequences of the conduct: for example, not appreciating that one is cutting a human throat rather than cutting bread, or not appreciating that an act will cause physical harm. It is not enough that the defendant knew the physical nature of the act but misjudged its moral significance. The second limb is that the defendant did not know that what he was doing was wrong. In English law, wrong means legally wrong, not merely morally wrong. Windle is the principal authority: a defendant who knew he would be punished was treated as knowing that the act was wrong. This is one of the most controversial aspects of the doctrine.

The case law is not merely illustrative; it is the doctrine. M'Naghten supplies the governing test. Its importance lies in the cognitive structure of the defence: disease of the mind, defect of reason, and lack of knowledge as to the nature and quality of the act or its wrongness. The rules have survived sustained criticism because they are simple, restrictive and administrable. Their weakness is that they fail to accommodate disorders of control.

Kemp is the foundation of the broad legal meaning of disease of the mind. The defendant’s arteriosclerosis caused a temporary loss of consciousness during which he attacked his wife. Devlin J held that disease of the mind is concerned with the mind’s functioning, not with whether the condition is psychiatric. This moved insanity away from ordinary language and made bodily conditions affecting mental functioning potentially relevant.

Quick marks the opposite side of the line. A diabetic nurse assaulted a patient after taking insulin and insufficient food. The Court of Appeal treated hypoglycaemia caused by insulin as an external factor capable of founding automatism. The decision is indispensable because it demonstrates that diabetes does not automatically equal insanity. One must identify the immediate cause of the malfunction.

Sullivan confirms that epilepsy is insanity for legal purposes. The House of Lords rejected the argument that the label should be confined to diseases of the brain or conditions permanently impairing reason. A transient epileptic episode could be a disease of the mind. The decision emphasises internal cause and recurrence. It also shows the law’s willingness to impose the special verdict even where the defendant may appear far removed from lay notions of insanity.

Hennessy is usually paired with Quick. Hyperglycaemia caused by diabetes and failure to take insulin was held to be internal, and therefore insanity. The contrast between insulin-induced hypoglycaemia and disease-induced hyperglycaemia is artificial but examinable. It is a classic problem-question hinge.

Burgess extended the internal approach to sleepwalking. The defendant violently attacked a friend while asleep. The Court of Appeal treated sleepwalking, on the facts, as arising from an internal disorder and carrying a risk of recurrence. The case is often criticised because ordinary sleep is universal, but the court focused on abnormal sleep disorder producing violence.

T shows that psychological trauma may, in exceptional cases, produce automatism. A rape complainant later participated in robbery and claimed dissociative automatism. The Court of Appeal accepted that an external shocking event might found automatism. The case should be used carefully: not every stress reaction is automatism, and mere panic is insufficient.

Attorney-General's Reference (No 2 of 1992) restrains expansive claims. Driving without full conscious awareness is not enough. The defendant must show total destruction of voluntary control. This case is crucial in driving scenarios, where students are tempted to equate inattention or fatigue with automatism.

See practice questions section below.

See further reading section below.