Introduction
In the criminal law of England and Wales, for a defendant to be found guilty of a result crime, such as murder or criminal damage, the prosecution must prove beyond a reasonable doubt that the defendant’s conduct caused the prohibited result. Causation provides the essential link between the defendant's act or omission and the consequence that forms the basis of the charge. The legal doctrine of causation is not always straightforward and has been developed by the courts over many years. The law has established a two-part test to determine causation. First, the prosecution must establish factual causation. Second, they must also prove legal causation. This essay will explain these two stages of the causation test, using case law to illustrate how the principles are applied. It will also discuss the concept of a ‘novus actus interveniens’, or a new intervening act, which can break the chain of causation and relieve the defendant of criminal liability for the final result.
Factual Causation
The first step in establishing causation is to determine whether the defendant's act was a factual cause of the result. The test for factual causation is the 'but for' test. This asks: '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 what the defendant did, then factual causation is not established, and the defendant cannot be found guilty of the result crime.
The classic authority for this principle is the case of R v White (1910). In this case, the defendant put cyanide in his mother's drink with the intention of killing her. His mother drank some of the drink but later died of a heart attack, which was unrelated to the poison. Medical evidence showed that she would have died at that moment regardless of the defendant's actions. Applying the 'but for' test, it could not be said that 'but for' the defendant putting poison in the drink, his mother would not have died. Therefore, his act was not the factual cause of her death. He was acquitted of murder, although he was found guilty of attempted murder. The White case clearly demonstrates that if the defendant’s act is not a factual cause of the result, the enquiry into causation ends there.
Legal Causation
Once factual causation is established, the prosecution must then prove legal causation. The 'but for' test is very wide and can include many different causes for a single event. For example, 'but for' the victim being born, they would not have been killed. The principles of legal causation exist to narrow down the scope of liability to only those causes that are significant enough for the law to attach criminal responsibility. For legal causation to be established, the defendant's conduct must be an 'operating and substantial' cause of the result (R v Smith, 1959).
The term 'substantial' does not mean that the defendant's act has to be the only or even the main cause of the result. It simply means that the cause must be more than minimal or trivial. In R v Kimsey (1996), the Court of Appeal approved a direction to the jury that the defendant's driving did not need to be the "principal or a substantial cause" of a fatal car crash, but that it was enough if it was "a cause and something more than a slight or trifling link". This shows that as long as the defendant’s contribution is not insignificant, it can be considered a legal cause.
Furthermore, the defendant's act must be 'operating' at the time of the result. This means that there must be a clear link between the initial act and the resulting harm. This link is often referred to as the 'chain of causation'. If this chain is broken by a new intervening act (a novus actus interveniens), then the defendant's act is no longer considered an operating cause, and legal causation will not be established.
Novus Actus Interveniens: Breaking the Chain of Causation
An intervening act can come from the victim, a third party, or even be a natural event. The law has developed different tests to decide whether such an act is sufficient to break the chain of causation.
Acts of the Victim
If the victim does something in reaction to the defendant's act that leads to the prohibited result, the question is whether that reaction breaks the chain of causation. The general rule is that a foreseeable reaction by the victim will not break the chain. In R v Roberts (1971), a young woman was injured when she jumped out of a moving car to escape the defendant's unwanted sexual advances. The court held that her action did not break the chain of causation because it was a reasonably foreseeable consequence of what the defendant was doing. The test established was whether the victim's act was "so daft… or so unexpected… that no reasonable man could be expected to foresee it".
Another important principle is the 'thin skull' or 'egg-shell skull' rule, which means the defendant must take their victim as they find them. This applies not just to physical conditions but also to the victim's beliefs. In R v Blaue (1975), the victim was stabbed by the defendant and required a blood transfusion to save her life. She was a Jehovah's Witness and refused the transfusion on religious grounds, and subsequently died. The defendant argued that her refusal broke the chain of causation. The court rejected this argument, stating that the defendant had to take the victim as he found her, not just in terms of her physical health but also her "whole person", which included her religious beliefs. The stab wound was still an operating cause of death.
Acts of a Third Party
An act of a third party will only break the chain of causation if it is a "free, deliberate and informed" act that is independent of the defendant's initial wrongdoing (R v Pagett, 1983). In Pagett, the defendant, who was armed, used his pregnant girlfriend as a human shield while he shot at police. The police returned fire, and the girlfriend was killed by a police bullet. The defendant was convicted of her manslaughter. The court held that the police officers' actions were not a 'novus actus interveniens' because they were acting in self-defence and in performance of their legal duty. Their actions were a foreseeable and direct consequence of the defendant's actions, and not a free, deliberate, and informed act that broke the chain of causation.
A key case in this area is R v Kennedy (No 2) (2007). The defendant supplied the victim with a prepared syringe of heroin. The victim self-injected the heroin and died. The House of Lords held that the defendant was not guilty of manslaughter because the victim's act of injecting himself was a free, voluntary, and informed act. This voluntary act by the victim broke the chain of causation, meaning the defendant was not the legal cause of death.
Medical Treatment
Courts are generally reluctant to allow medical treatment to break the chain of causation. The general principle, from R v Smith (1959), is that if the original injury inflicted by the defendant is still an operating and substantial cause of death, then poor medical treatment will not break the chain. In Smith, a soldier was stabbed by the defendant during a fight. He was dropped twice on the way to the medical station, and the treatment he received was described as "thoroughly bad". Despite this, the court held that the stab wound was still the operating cause of death, and the conviction for murder was upheld.
A subsequent case, R v Cheshire (1991), refined this principle. The court stated that medical negligence would only break the chain of causation if it was "so independent of the defendant's acts, and in itself so potent in causing death" that the jury would regard the defendant's acts as insignificant. In Cheshire, the victim's gunshot wounds from the defendant had largely healed, but he died from complications arising from a tracheotomy performed by doctors. The court held that these complications were a direct result of the defendant's actions and did not break the chain of causation. This sets a very high threshold, meaning it is very rare for medical treatment to be considered a 'novus actus interveniens'.
Conclusion
In conclusion, the doctrine of causation in criminal law is fundamental to ensuring that only those who are genuinely responsible for a prohibited result are convicted. The two-stage test of factual and legal causation provides the basic framework for this process. Factual causation is established by the simple 'but for' test, as shown in White. Legal causation is more complex and involves a judgement that the defendant's act was an operating and substantial cause of the result. The courts have developed a body of case law to deal with intervening acts, which shows a reluctance to allow a defendant to escape liability. Whether the intervening act is from the victim, a third party, or medical professionals, the chain of causation will generally only be broken if the act is truly independent, voluntary, and significant enough to make the defendant's original act no longer an operating cause. While the principles are established, their application can sometimes appear to be influenced by policy, particularly the desire not to absolve the original wrongdoer of responsibility for the ultimate harm.
References
R v Blaue [1975] 1 WLR 1411
R v Cheshire [1991] 1 WLR 844
R v Kennedy (No 2) [2007] UKHL 38
R v Kimsey [1996] Crim LR 35
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
Ormerod, D. and Laird, K. (2021) Smith, Hogan, and Ormerod's Criminal Law. 16th edn. Oxford University Press.
