Introduction: Why Mental Capacity Defences Matter
Welcome to one of the most fascinating parts of criminal law! Usually, to find someone guilty, the prosecution must prove they committed a criminal act (actus reus) and had a guilty mind (mens rea). But what happens if the person's mind wasn't working properly?
In this chapter, we look at three "mental capacity" defences: Insanity, Automatism, and Intoxication. These defences are important because the law tries to be fair. It asks: Is it right to punish someone who couldn't control their actions or didn't understand what they were doing? Let's dive in!
1. Insanity: The "M’Naghten Rules"
Don't worry if this seems a bit "old-fashioned" at first—the rules for insanity were actually created in 1843! In law, insanity doesn't mean the same thing it does to a doctor. It is a legal definition, not a medical one.
The Starting Point
The law assumes everyone is sane and responsible for their actions. If a defendant wants to claim they were insane, the burden of proof is on them to prove it (on the balance of probabilities).
The M’Naghten Rules
To use this defence, the defendant must prove that at the time of the act, they were suffering from a defect of reason caused by a disease of the mind, which meant they didn't know the nature and quality of their act, or that it was wrong.
1. Defect of Reason: This means the person’s power of reasoning was impaired. It’s more than just being forgetful or confused (as seen in the case of Clarke).
2. Disease of the Mind: This is the part that surprises many students! It can be a mental illness, but it can also be a physical condition that affects the brain, like epilepsy, diabetes, or even sleepwalking. The key is that the cause must be internal (coming from inside the body).
3. Nature and Quality / Knowing it was Wrong: The defendant either didn't know what they were doing (e.g., they thought they were cutting a loaf of bread, but it was a person) or they knew what they were doing but didn't know it was legally wrong (Windle).
Quick Review Box:
- Internal Cause = Insanity.
- External Cause = Automatism.
- Key Case: M’Naghten (1843).
The Verdict
If the defence is successful, the jury gives a special verdict: "Not guilty by reason of insanity." This doesn't mean the person just walks free. Under the Criminal Procedure (Insanity and Unfitness to Plead) Act 1991, the judge can order a hospital order, a supervision order, or an absolute discharge.
Takeaway: Insanity is about an internal problem that stops someone from understanding their actions or the law.
2. Automatism (Non-Insane Automatism)
Imagine your body is moving, but your "brain's pilot" has completely left the cockpit. This is automatism.
What is it?
Legal scholar Lord Denning defined it in the case of Bratty as an act done by the muscles without any control by the mind. Because there is no control, there is no actus reus (voluntary act) and no mens rea.
The Two Rules for Automatism
1. It must be caused by an External Factor: Unlike insanity, the cause must come from outside the body.
Examples: A swarm of bees attacking you, being hit on the head, or taking the wrong medication (if not self-induced).
2. There must be a Total Loss of Control: If the defendant has even a little bit of control (partial control), the defence will fail (Broome v Perkins).
Did you know? A classic example of the difference between insanity and automatism is diabetes. If a diabetic has a "hypo" because they took insulin but didn't eat (external factor), it is automatism. If they have a "hyper" because of the disease itself (internal factor), it is insanity.
Self-Induced Automatism
If the defendant caused their own state (e.g., by drinking too much or taking illegal drugs), they usually cannot use the defence of automatism. They would have to look at the rules for intoxication instead.
Takeaway: Automatism is a "get out of jail free" card (a complete acquittal) because the person had no control due to an external event.
3. Intoxication
This is when a person is under the influence of alcohol, drugs, or other substances. The law is quite strict here because it doesn't want people using "I was drunk" as an easy excuse for a crime.
The Big Distinction: Voluntary vs. Involuntary
1. Involuntary Intoxication: This is when you didn't mean to get intoxicated.
Examples: Your drink was spiked, or you had an unexpected reaction to medicine prescribed by a doctor.
The Rule: If you were so intoxicated that you couldn't form the mens rea, you are not guilty.
2. Voluntary Intoxication: This is when you chose to drink or take drugs. To decide if this is a defence, we use the Majewski rule, which looks at the type of crime committed.
Specific Intent vs. Basic Intent Crimes
This is where students often get stuck, but there is a simple trick to remember it!
Specific Intent Crimes (The "Serious" ones): Crimes that require intention only.
Examples: Murder, Section 18 GBH, Theft, Robbery.
Rule: If the defendant was so drunk they couldn't form the intent, the charge can be reduced to a lesser crime.
Basic Intent Crimes: Crimes that can be committed recklessly.
Examples: Manslaughter, Assault, Battery, Section 20 GBH.
Rule: Voluntary intoxication is no defence. The law says that getting drunk is a reckless act in itself, so you've already provided the "guilty mind."
Mnemonic for Majewski:
Specific Intent = Sometimes a defence (can reduce the charge).
Basic Intent = Bad luck (no defence).
Common Mistake to Avoid!
A "drunken intent is still an intent." If the defendant is drunk but still knows what they are doing and intends to do it, the defence fails (Sheehan and Moore).
Takeaway: Intoxication is only a partial defence for "Specific Intent" crimes and only if the defendant was so far gone they couldn't form an intention.
Final Summary Table
Defence: Insanity
Cause: Internal (Disease of the mind)
Result: Not Guilty by Reason of Insanity (Treatment/Hospital)
Defence: Automatism
Cause: External (e.g., blow to the head)
Result: Complete Acquittal (Walks free)
Defence: Intoxication
Cause: Alcohol/Drugs
Result: Depends on if it was voluntary and the type of crime.
Keep practicing with scenarios! If you see a question about a sleepwalker, think "Insanity" (Internal). If you see a "spiked drink," think "Involuntary Intoxication." You've got this!