3.2 - Capacity defences

Paper 1 Capacity Issues

Capacity defences ask whether D should be held criminally responsible when D's mental state, physical condition or intoxication affects voluntary control or fault. The AQA specification places them in criminal law after the general elements of liability, so they must be used with actus reus and mens rea, not instead of them.

The central question is different for each defence:

Capacity issues connect to three AQA themes. First, criminal liability normally requires voluntary conduct. If D's movement is not voluntary, actus reus may fail. Secondly, many offences require fault through intention, recklessness or another mental element. If D cannot form that mens rea, liability may fail or reduce. Thirdly, the law protects the public by limiting these defences: it does not excuse every mental disorder, every loss of concentration, or every self-induced drunken mistake.

The first exam skill is route selection. Do not write all three defences because a scenario mentions unusual behaviour. Ask what is actually affected:

1. If the facts suggest a recognised mental condition or internal condition affecting reasoning, start with insanity.
2. If the facts suggest a total loss of voluntary control from an external cause, start with automatism.
3. If the facts mention alcohol, drugs or medication affecting mens rea, classify intoxication and then classify the offence.

Insanity: M'Naghten Elements

Insanity is a general defence at common law, but the word is legal rather than medical. It does not simply mean that D has a psychiatric diagnosis. The M'Naghten rules provide the AQA framework.

The defence must establish, on the balance of probabilities, that at the time of the act:

1. D had a defect of reason.
2. The defect of reason came from a disease of the mind.
3. Because of that defect, D either did not know the nature and quality of the act, or lacked knowledge of wrongness: under current Keal guidance, D must not know it was unlawful or wrong by ordinary reasonable standards.

Mere absent-mindedness, forgetfulness or failure to think carefully is not enough. The defect must affect reasoning, not just emotions or self-control.

AQA's own materials emphasise that disease of the mind can result from physical disease, so do not assume it must be a psychiatric illness. The key exam move is to explain why the condition is being treated as internal to D and why it affects reasoning.

The final element is the knowledge requirement. D must either not know the nature and quality of the act, meaning D does not understand what he is physically doing or its physical consequences, or not know that it is wrong in law. Windle establishes that knowledge that the act is legally prohibited defeats the wrongness limb. Current guidance also applies Keal (2022): D must not know the act is contrary to law or wrong by the standards of ordinary reasonable people. Knowledge of either defeats that limb; D's personal moral approval is insufficient. A factual delusion alone does not settle whether D lacked the required knowledge.

If insanity succeeds, D is not simply acquitted in the ordinary way. The jury returns the special verdict of not guilty by reason of insanity. AQA mark schemes reward this legal consequence because it shows the public protection side of the defence as well as the responsibility side.

Use the cases as tools:

Do not confuse insanity with diminished responsibility. Diminished responsibility is a partial defence to murder only and reduces murder to voluntary manslaughter. Insanity can apply beyond murder, but it requires the stricter M'Naghten structure and leads to the special verdict.

Automatism: Total Involuntariness

Automatism is concerned with involuntary conduct. It is usually described as a complete defence because, if D's conduct was not voluntary, the prosecution cannot prove the required actus reus. AQA's general criminal liability content expressly includes voluntariness and involuntariness, so automatism is not a side issue: it goes to the foundation of liability.

For non-insane automatism, the operational test is:

1. D suffered a total loss of voluntary control.
2. The loss of control was caused by an external factor.
3. D was not at fault in bringing about that state in a way that makes liability fair.

The threshold is high. Total loss means D's relevant act was not controlled by D's conscious mind. Partial control, reduced awareness, panic, clumsiness, memory loss or impaired judgement is not enough. Broome v Perkins is useful here because it supports the point that a defendant who retains some control, even while affected by a medical episode, will not usually satisfy automatism.

Hill v Baxter is a useful authority for the basic voluntariness principle. It illustrates that extraordinary events, such as being physically overcome or suddenly losing control through no fault of D, may mean the act is not voluntary. In a scenario, use it to support the need for a voluntary act before liability can be imposed.

Once sufficient evidence raises non-insane automatism, the prosecution must disprove it beyond reasonable doubt. Self-induced automatism is assessed through prior fault and the offence: it is not barred simply because D contributed to the condition, but reckless self-induction can defeat a basic-intent argument.

The source of the automatism matters. AQA materials recognise an external head injury as a possible basis for non-insane automatism. That is different from an internal condition affecting D's mind, which may point towards insanity instead. The legal consequence is also different: successful non-insane automatism produces a complete acquittal, while insanity produces the special verdict.

Be careful with reflexes. A reflexive movement may be involuntary, but you must still ask whether it caused the charged act. If D is able to perform a sequence of purposeful actions, such as choosing where to go, picking up an object and using it deliberately, the answer should usually question whether there was truly a total loss of control.

Internal And External Causes

The boundary between insanity and automatism is one of the most important parts of capacity defences. It is not a simple medical distinction. The law asks whether the cause of D's lack of capacity is treated as internal to D, pointing towards insanity, or external to D, pointing towards non-insane automatism.

Use this comparison:

AQA's sample material makes one point especially clear: disease of the mind can result from physical disease. Therefore, do not reject insanity just because the condition has a physical source. The legal question is whether the condition is treated as a disease of the mind for the M'Naghten rules.

Sullivan treats epilepsy as an internal disease-of-the-mind cause, so total seizure-related loss of control is normally analysed as insane automatism under M'Naghten, with the special verdict if proved, rather than automatic ordinary acquittal. Quick distinguishes hypoglycaemia caused by insulin as an external factor; Hennessy treats hyperglycaemia from diabetes and lack of insulin as internal. Cause, total control, medical evidence and any prior fault must all be examined.

By contrast, AQA assessment material treats a head injury suffered in an incident as capable of being an external factor for automatism. But that does not mean every injury or shock is enough. The application still has to show total involuntariness. If D performs a controlled sequence of acts after the injury, that fact weakens automatism.

This boundary also protects public safety. Insanity may be available where an internal condition makes D's reasoning legally defective, but the special verdict avoids treating D as an ordinary acquitted defendant. Non-insane automatism is narrower because it can lead to a complete acquittal where D is not responsible for the involuntary act.