Introduction
In English criminal law, for a defendant to be found guilty of a result crime, such as murder or criminal damage, the prosecution must prove a clear link between the defendant's act or omission and the prohibited consequence. This link is known as causation. Establishing causation is a fundamental step in assigning criminal liability, ensuring that a person is only held responsible for outcomes they have legally caused. The law has developed a two-stage test to determine this. First, the prosecution must establish 'factual causation', and second, they must prove 'legal causation'. Even if both are present, the chain of causation can be broken by a 'novus actus interveniens', which is a new intervening act. This essay will explain the principles of factual and legal causation, before analysing the different types of intervening acts that can break the chain of causation. It will be shown that while the core rules of causation are relatively clear, their application, particularly concerning intervening acts, can be complex and depends heavily on the specific facts of a case.
Factual Causation
The starting point for establishing causation is to determine whether the defendant's conduct was a factual cause of the result. The standard test for factual causation is the 'but for' test. The question asked is: 'but for' the defendant's conduct, would the result have occurred? If the answer is no, then the defendant is a factual cause of the result. If the result would have happened anyway, regardless of the defendant's actions, then there is no factual causation, and the defendant cannot be liable for that result.
The classic case illustrating this principle is R v White [1910] 2 KB 124. The defendant put cyanide in his mother's drink, intending to kill her. However, she died of a heart attack before she could drink a sufficient amount of the poison to be fatal. The medical evidence showed that her death was not caused by the poison. Applying the 'but for' test, it was clear that she would have died of the heart attack 'but for' the defendant putting poison in her drink. Therefore, his act was not the factual cause of her death. He could not be found guilty of murder, although he was convicted of attempted murder.
The 'but for' test provides a basic exclusionary rule. It filters out cases where the defendant's actions had no connection to the final outcome. However, the test is very wide. For example, 'but for' the defendant's parents meeting, the defendant would not have been born, and the crime would not have been committed. The test can therefore implicate many people or events in a chain of events leading to a result. Because of this, the law requires a second stage of enquiry to narrow down liability to those who are legally responsible.
Legal Causation
Once factual causation is established, the prosecution must also prove legal causation. This involves showing that the defendant’s act was a legally significant cause of the result. Unlike factual causation, this is not a scientific or philosophical question but a legal and moral one, used by the courts to decide whether it is fair to hold the defendant responsible (Herring, 2022). The main rule for legal causation is that the defendant's act must be an 'operating and substantial' cause of the result (R v Smith [1959] 2 QB 35).
The term 'substantial' means that the cause must be more than minimal or trivial. In R v Cato [1976] 1 WLR 110, the court held that a contribution to the result does not need to be the only or even the main cause, as long as it is not a 'slight or trifling' one. This means that as long as the defendant's act contributed to the end result in a more than minimal way, they can be seen as a legal cause. Furthermore, the defendant’s act need not be the only cause of the result. It is common for there to be multiple causes contributing to an outcome, and a defendant can be liable even if other causes are also present (R v Benge (1865) 4 F&F 504).
The requirement that the defendant's conduct be an 'operating' cause means that it must still be active in bringing about the result at the time it occurs. If something else happens after the defendant's act which renders the original act no longer a significant factor, the chain of causation may be broken. This leads to the doctrine of novus actus interveniens.
Novus Actus Interveniens: Breaking the Chain of Causation
A novus actus interveniens is a new act, from a third party, the victim, or a natural event, that intervenes between the defendant’s original act and the final outcome. For an act to be considered a novus actus interveniens, it must be sufficiently independent of the defendant’s act and so potent in causing the result that it renders the defendant's contribution no longer a significant cause (Ormerod and Laird, 2021). The courts have considered several categories of intervening acts.
Acts of the Victim
If the victim’s own actions contribute to their death or injury, this will not necessarily break the chain of causation. The general rule is that if the victim’s reaction is a reasonably foreseeable consequence of the defendant's act, the chain of causation will not be broken. In R v Roberts (1971) 56 Cr App R 95, a young woman jumped from a moving car to escape the defendant's unwanted sexual advances and was injured. The court held that the defendant was liable for her injuries, as her reaction was a natural result of his actions and was not 'so daft' as to be unforeseeable.
However, if the victim's reaction is disproportionate or unforeseeable, it may break the chain. In R v Williams and Davis [1992] 1 WLR 380, the victim jumped from a moving car and died, allegedly because the defendants were trying to rob him. The Court of Appeal stated that the jury should consider whether the victim's reaction was within the range of responses which might be expected from a victim placed in the situation he was. The victim’s own characteristics should be taken into account.
Furthermore, the 'thin skull rule' applies, which means the defendant must take their victim as they find them. In R v Blaue [1975] 1 WLR 1411, a victim of a stabbing refused a blood transfusion because she was a Jehovah's Witness. She died, and the defendant argued that her refusal broke the chain of causation. The court rejected this argument, holding that the defendant had to take the victim not just in their physical sense, but also in respect of their mind and religious beliefs. The stab wound was still an operating cause of death.
Acts of a Third Party
An act of a third party will generally break the chain of causation if it is 'free, deliberate and informed' and not a foreseeable consequence of the defendant’s act. However, if the third party's action is itself a reaction to the situation created by the defendant, it is less likely to break the chain. In R v Pagett (1983) 76 Cr App R 279, the defendant, resisting arrest, held his pregnant girlfriend as a human shield and fired at police officers. The officers returned fire, killing the girlfriend. The defendant was convicted of her manslaughter. The court held that the police officers’ actions were not a free and voluntary act but an act of self-preservation and a performance of their legal duty. As their actions were a foreseeable consequence of the defendant firing at them, their conduct did not break the chain of causation from the defendant’s acts to the victim’s death.
Medical Intervention
Cases involving medical treatment that is administered to a victim after they have been injured by the defendant have proved difficult for the courts. The general principle is that negligent medical treatment is unlikely to break the chain of causation. In R v Smith [1959] 2 QB 35, a soldier was stabbed by the defendant. He was dropped twice on the way to the medical station and then received treatment which was described as 'thoroughly bad'. He died, but the court held that the stab wound was still an 'operating and substantial cause' of his death, so the defendant remained liable. The chain of causation would only be broken if the second cause was so overwhelming as to make the original wound merely part of the history.
An exception was found in R v Jordan (1956) 40 Cr App R 152, where the victim was stabbed and taken to hospital. His wound was healing well, but he was given an antibiotic to which he had shown he was allergic. This was described as 'palpably wrong' treatment. The court held that this did break the chain of causation. However, Jordan has been described as a case with very specific facts.
The modern leading case is R v Cheshire [1991] 1 WLR 844. The victim was shot by the defendant and required a tracheotomy tube in hospital. Weeks later, his windpipe narrowed due to the tracheotomy scar, and he died. The defendant argued the doctors' failure to recognise this complication broke the chain of causation. The Court of Appeal upheld the murder conviction, stating that medical negligence would only break the chain of causation if it was so independent of the defendant's acts and so potent in causing death, that the jury would regard the defendant's acts as insignificant. This is a very high threshold, meaning that only in the most exceptional cases will medical treatment, even if negligent, break the chain of causation.
Conclusion
In conclusion, the doctrine of causation in English criminal law is a two-stage process. The 'but for' test establishes factual causation, and the 'operating and substantial cause' test establishes legal causation. While these principles appear straightforward, their application becomes more complex in cases involving a novus actus interveniens. The case law shows that the courts are generally reluctant to find that the chain of causation has been broken, particularly by the victim's own actions or by medical negligence. The key questions often revolve around the foreseeability of the intervening act and whether the defendant’s original act can still be considered a significant and operating cause of the final result. Although the courts have provided tests such as the 'daftness' test and the Cheshire test, these principles are flexible and their application remains highly fact-dependent, which can lead to a degree of uncertainty. Ultimately, the rules of causation are a mechanism for the courts to assign legal responsibility, a process that is guided by legal principle but is also influenced by considerations of fairness and policy.
References
Herring, J. (2022) Criminal Law: Text, Cases, and Materials. 10th edn. Oxford University Press.
Ormerod, D. and Laird, K. (2021) Smith, Hogan, and Ormerod's Criminal Law. 16th edn. Oxford University Press.
R v Benge (1865) 4 F&F 504.
R v Blaue [1975] 1 WLR 1411.
R v Cato [1976] 1 WLR 110.
R v Cheshire [1991] 1 WLR 844.
R v Jordan (1956) 40 Cr App R 152.
R v Pagett (1983) 76 Cr App R 279.
R v Roberts (1971) 56 Cr App R 95.
R v Smith [1959] 2 QB 35.
R v White [1910] 2 KB 124.
R v Williams and Davis [1992] 1 WLR 380.
