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This lesson covers the actus reus — the "guilty act" — which is one of the two essential elements that must be proved to establish criminal liability. Along with mens rea (the guilty mind), actus reus forms the foundation of virtually every criminal offence in English law. You must understand what constitutes a voluntary act, when a failure to act (an omission) can give rise to criminal liability, and how the rules of causation link the defendant's conduct to the prohibited consequence.
| Term | Definition |
|---|---|
| Actus reus | The physical element of a crime; the guilty act, omission, or state of affairs |
| Voluntary act | A conscious, deliberate act performed by the defendant of their own free will |
| Omission | A failure to act that may, in limited circumstances, give rise to criminal liability |
| Duty of care | A legal obligation to act in certain situations, breach of which can form the actus reus |
| Factual causation | The "but for" test — but for the defendant's act, would the result have occurred? |
| Legal causation | The defendant's act must be a substantial and operating cause of the prohibited consequence |
| Novus actus interveniens | A new intervening act that breaks the chain of causation between the defendant's conduct and the result |
| Thin skull rule | The defendant must take the victim as they find them, including any pre-existing vulnerabilities |
The actus reus is the external, physical element of a criminal offence. It encompasses:
Not every offence requires all three. Some offences are conduct crimes (the act itself is the offence, such as perjury), while others are result crimes (a specific consequence must be caused, such as murder or ABH).
The act must be voluntary — that is, performed consciously and of the defendant's own free will. If the defendant's body moves involuntarily (e.g., during an epileptic seizure, a reflex, or while being physically compelled by another person), the actus reus is not established.
In Hill v Baxter [1958], the court gave examples of involuntary acts that would negate actus reus: being attacked by a swarm of bees while driving, having a heart attack, or being struck on the head causing unconsciousness. The defendant must have had some conscious control over their bodily movements.
Exam Tip: Always begin your answer by identifying the actus reus of the offence in question. State what the prosecution must prove — the act, the circumstances, and (if a result crime) the consequence.
English criminal law generally imposes no duty to act. There is no general "Good Samaritan" law requiring bystanders to rescue others. However, the law recognises several exceptions where a person is under a duty to act, and a failure to fulfil that duty can constitute the actus reus of an offence.
The following table summarises the recognised duties to act and the leading cases:
| Duty | Description | Key Case |
|---|---|---|
| Contractual duty | Where the defendant's contract of employment creates a duty to act | R v Pittwood [1902] |
| Duty arising from a relationship | A special relationship (e.g., parent–child) imposes a duty of care | R v Gibbins and Proctor [1918] |
| Voluntary assumption of duty | Where the defendant voluntarily undertakes care of another person | R v Stone and Dobinson [1977] |
| Duty from creating a dangerous situation | Where the defendant's own act creates a risk, they have a duty to minimise it | R v Miller [1983] |
| Statutory duty | An Act of Parliament creates a duty to act | e.g., s.1 Children and Young Persons Act 1933; s.170 Road Traffic Act 1988 |
| Duty arising from public office | A public official has a duty to act within their role | R v Dytham [1979] |
Pittwood was a railway crossing keeper whose contractual duty required him to close the gate when a train was approaching. He left the gate open, and a person crossing the tracks was killed by a train. The court held that his contractual duty to close the gate meant that his failure to do so amounted to the actus reus of manslaughter.
Principle: A contract of employment can create a duty to act, breach of which can form the actus reus.
A father (Gibbins) and his partner (Proctor) failed to feed the father's seven-year-old child, who died of starvation. Gibbins was liable because of his parental duty to provide for his child. Proctor was liable because she had voluntarily assumed a duty of care by taking on the role of caring for the child and receiving housekeeping money for that purpose.
Principle: Parents owe a duty of care to their children. A person who voluntarily assumes responsibility for a vulnerable person also owes a duty of care.
Stone and his partner Dobinson took Stone's elderly sister, Fanny, into their home. Fanny became increasingly ill and eventually died from malnutrition and self-neglect. The defendants had made some (inadequate) efforts to find help. The Court of Appeal upheld their conviction for gross negligence manslaughter. By taking Fanny into their home, they had voluntarily assumed a duty of care towards her.
Principle: Once a person voluntarily assumes a duty of care, they must take reasonable steps to discharge it. Failure to do so can amount to the actus reus.
Miller, a squatter, fell asleep while smoking a cigarette. He woke to find his mattress on fire. Instead of attempting to extinguish the fire or calling the fire brigade, he simply moved to another room and went back to sleep. The fire spread, causing significant damage. The House of Lords held that by creating a dangerous situation (the fire), Miller came under a duty to take reasonable steps to counteract the danger.
Principle: A person who inadvertently creates a dangerous situation has a duty to take reasonable steps to minimise the risk. This is sometimes called the Miller principle or the duty from creating a dangerous situation.
flowchart TD
A[Has the defendant failed to act?] -->|Yes| B{Does a recognised duty to act exist?}
A -->|No| C[Consider whether a positive act forms the actus reus]
B -->|Contractual duty| D[R v Pittwood]
B -->|Relationship duty| E[R v Gibbins and Proctor]
B -->|Voluntary assumption| F[R v Stone and Dobinson]
B -->|Created danger| G[R v Miller]
B -->|Statutory duty| H[Statute imposes duty]
B -->|Public office| I[R v Dytham]
B -->|No duty exists| J[No actus reus — no liability]
D --> K[Actus reus established through omission]
E --> K
F --> K
G --> K
H --> K
I --> K
Exam Tip: When answering a problem question on omissions, always (1) identify that the defendant has failed to act, (2) consider whether a recognised duty exists, (3) apply the relevant case authority to the facts, and (4) conclude whether the actus reus is satisfied.
For result crimes (offences where a specific consequence must be proved, such as murder, manslaughter, or ABH), the prosecution must establish a causal link between the defendant's act and the prohibited result. Causation has two stages: factual causation and legal causation.
The first stage asks: but for the defendant's act, would the prohibited consequence have occurred?
White put potassium cyanide into his mother's drink intending to kill her. However, she died of a heart attack before the poison took effect. The medical evidence showed that the poison did not cause or accelerate her death. Applying the "but for" test: but for White putting poison in the drink, would his mother have died? Yes — she would have died of the heart attack anyway. Therefore, factual causation was not established for murder. White was instead convicted of attempted murder.
Principle: If the consequence would have occurred regardless of the defendant's act, factual causation is not satisfied.
Even where factual causation is established, the prosecution must also show that the defendant's act was a legally significant cause of the result. The defendant's act need not be the sole or even the main cause — it must be more than a minimal (de minimis) contribution to the result.
A soldier (Smith) stabbed a fellow soldier during a barrack-room fight. The victim was dropped twice while being carried to the medical officer and then received treatment described as "thoroughly bad" — in fact, the treatment probably made his condition worse. The victim died. The court held that the original stab wound was still an operating and substantial cause of death, despite the poor medical treatment. Legal causation was established.
Principle: The defendant's act need not be the sole cause of death. As long as it remains an operating and substantial cause, legal causation is satisfied — even if there are other contributing factors.
The defendant must take the victim as they find them. If the victim has a pre-existing condition or vulnerability that makes the consequences of the defendant's act more severe than they would otherwise be, the defendant is still liable for the full extent of the harm.
Blaue stabbed a young woman, a Jehovah's Witness, who refused a blood transfusion on religious grounds. She died from blood loss. Blaue argued that the refusal of treatment broke the chain of causation. The Court of Appeal rejected this argument, holding that the defendant had to take his victim as he found her — including her religious beliefs. The thin skull rule applied and causation was not broken.
Principle: The thin skull rule extends not only to physical conditions but also to the victim's religious beliefs and personal characteristics.
A novus actus interveniens is a subsequent event that may break the chain of causation between the defendant's act and the prohibited result. If the chain is broken, the defendant is not liable for the consequence.
Three main categories of intervening act are recognised:
| Category | Test | Key Cases |
|---|---|---|
| Act of the victim | Was the victim's response reasonably foreseeable? | R v Roberts [1971], R v Williams and Davis [1992] |
| Act of a third party | Was the third party's act so overwhelming as to render the defendant's act insignificant? | R v Jordan [1956], R v Smith [1959], R v Cheshire [1991] |
| Natural event | Was the natural event extraordinary and unforeseeable? | Rarely arises in case law |
Roberts was driving and made unwanted sexual advances towards his female passenger. She jumped from the moving car and suffered injuries. The court held that her reaction was reasonably foreseeable in the circumstances. The chain of causation was not broken because the victim's response was within the range of responses that could reasonably be expected.
Principle: If the victim's own act is a reasonably foreseeable response to the defendant's conduct, it will not break the chain of causation.
Jordan stabbed the victim, who was taken to hospital. The stab wound was healing well, but a doctor administered an antibiotic to which the victim was known to be allergic. The victim died. The Court of Criminal Appeal quashed the conviction, holding that the medical treatment was "palpably wrong" and constituted a novus actus interveniens that broke the chain of causation.
Principle: Medical treatment that is so independent of the defendant's act and so potent in causing death will break the chain of causation. However, this is an exceptional and rarely applied decision. In most cases, even poor medical treatment will not break the chain (see R v Smith, R v Cheshire).
flowchart TD
A[Did D commit an act or omission?] -->|Yes| B{Factual causation: But for D's act, would V have suffered the harm?}
A -->|No| Z[No actus reus]
B -->|No — harm would have occurred anyway| C[Factual causation NOT established — R v White]
B -->|Yes — D's act was a necessary condition| D{Legal causation: Was D's act a substantial and operating cause?}
D -->|Yes| E{Was there a novus actus interveniens?}
D -->|No — D's contribution was minimal| F[Legal causation NOT established]
E -->|No intervening act| G[Causation established]
E -->|Victim's act| H{Was victim's response reasonably foreseeable? — R v Roberts}
E -->|Third party / medical| I{Was treatment palpably wrong? — R v Jordan vs R v Smith}
H -->|Yes — foreseeable| G
H -->|No — daft and unexpected| J[Chain broken — no causation]
I -->|Treatment not palpably wrong| G
I -->|Treatment palpably wrong| J
E -->|Consider thin skull rule| K[D takes V as they find them — R v Blaue]
K --> G
| Arguments For | Arguments Against |
|---|---|
| Protects vulnerable people who depend on others | May criminalise those who are themselves vulnerable or incapable (e.g., R v Stone and Dobinson) |
| Upholds moral duties in close relationships | English law values personal autonomy — a general duty to rescue would be an excessive interference with liberty |
| The duty categories are clearly defined and limited | Difficult to draw the line — where does a "voluntary assumption" begin and end? |
| Consistent with the principle that creating danger imposes responsibility (R v Miller) | The law should punish positive acts more severely than failures to act |
This content is aligned with the AQA A-Level Law specification.