Introduction
The Latin term novus actus interveniens, literally translating to "a new act intervening," signifies a critical legal principle concerning causation, particularly within the realms of tort and criminal law. The concept dictates that a causal link between a defendant's actions and the ultimate harm suffered by a claimant or victim can be severed by the introduction of an intervening act. For a successful claim in negligence or criminal culpability, it is not enough to establish that a defendant's act was a cause; it must also be shown to be the legal cause. Novus actus interveniens serves as a mechanism to assess whether a subsequent action is sufficient to break this chain of causation, thereby relieving the initial actor of liability. The key requirements for this principle to apply involve demonstrating that the intervening act was both voluntary and unforeseeable, thus disrupting the natural progression of events originating from the defendant's initial conduct. This concept provides a complex framework for determining responsibility and legal culpability.
The Fundamental Principles of Novus Actus Interveniens
The application of novus actus interveniens rests on several core tenets which guide judicial analysis. One central aspect is the requirement of a truly intervening act, meaning it should not merely be a consequence or result of the initial action. This intervening act must introduce an entirely separate cause of harm. Additionally, this act must be voluntary in nature, emanating from the free will of either the claimant, a third party or even natural events, rather than being a forced or directly predictable response to the defendant’s actions. If the subsequent act is a direct, foreseeable outcome of the defendant’s conduct, it is not a true novus actus interveniens. The law generally presumes free will for adults of sound mind, an idea highlighted in R v Kennedy [2007]. Moreover, the test for determining the chain of causation has shifted. In R v Wallace [2018], the Court of Appeal stated that a question that requires answering is “were the injuries inflicted by the defendant an operating and significant cause of death?”, moving from the ‘operating and substantial’ test, indicating that even if a jury was persuaded that a later cause was the main cause of death, the initial injury could still be considered a significant cause.
Voluntary Acts and the Breaking of the Chain
An important consideration is whether the intervening act was a voluntary and informed choice. A frequently cited case to this point is R v Kennedy [2007], wherein the House of Lords overturned a conviction for manslaughter. In this case, the defendant prepared a syringe of heroin for the victim, who then self-administered the drug, ultimately dying. The court held that the victim’s voluntary and informed choice to inject the heroin constituted a novus actus interveniens, thereby breaking the chain of causation between the defendant’s actions of supplying the heroin and the victim’s death. Lord Bingham stated that the law generally treats "informed adults of sound mind...as autonomous beings able to make their own decisions," indicating that their free choices can effectively remove liability from an original wrongdoer. This principle emphasizes that a person who makes a fully voluntary decision to act in a certain way is responsible for the consequences of that choice, not the person whose prior actions may have enabled the choice. The crucial element is that the choice is made freely without coercion. The case of R v Wallace [2018], which addresses a victim's request for euthanasia following a severe assault, provides a contrast. In this case the court argued that “Mr. van Dongen’s death, his request to the doctors, and the act of euthanasia itself carried out in accordance with his wishes, were not discrete acts or events independent of the defendant’s conduct, nor were they voluntary, if by this is meant they were the product of the sort of free and unfettered volition presupposed by the novus actus rule”.
Reasonable Acts and the Preservation of Causation
In contrast to voluntary acts that break the chain of causation, certain kinds of subsequent actions, notably those taken in self-preservation or in response to a legal duty, generally do not qualify as novus actus interveniens. The case of R v Pagett (1983) illustrates this point. Here, the defendant used a hostage as a human shield and was involved in a shoot out with the police, where the hostage was subsequently killed. The Court of Appeal upheld his conviction for manslaughter, reasoning that the police officer's return fire did not constitute a novus actus interveniens. Robert Goff LJ noted that “a reasonable act performed for the purpose of self-preservation, being of course itself an act caused by the accused’s own act, does not operate as a novus actus interveniens.” Self-preservation extends to self-defence and acts taken in the execution of a legal duty, affirming that actions taken in response to an immediate danger do not break the chain. This principle upholds that a person should not be penalized for actions reasonably necessary to preserve life or fulfill a duty where the need is caused by the defendant’s conduct. This emphasizes that the causal link remains if the intervening act is a response to a dangerous situation created by the initial wrongdoer. This position is also further supported by Haynes v Harwood [1935] where a police officer was injured stopping the defendant's runaway horses, where it was found that the act of the plaintiff was “the natural and probable consequences of the defendants’ negligence”.
The Role of Unreasonable Conduct and Contributory Negligence
Where the claimant or victim acts unreasonably, this can disrupt the chain of causation. In McKew v Holland and Hannen [1969] a claimant had previously sustained an injury at work that resulted in a weak leg. The claimant later descended a steep staircase without a handrail alone, and his weak leg gave way, resulting in a further injury. The court found that the claimant's actions were unreasonable and constituted a novus actus interveniens, thus breaking the chain of causation. Lord Reid noted that “if the injured man acts unreasonably, he cannot hold the defender liable for injury caused by his own unreasonable conduct.” This contrasts with cases such as Spencer v Wincanton Holdings [2009], where the claimant, who had previously had a leg amputated because of the defendant's negligence, tried to fill his car with petrol, tripped and fell and became wheelchair bound. In this case, it was found the claimant’s actions, though unwise, did not meet the threshold of unreasonableness required to be a novus actus interveniens, and instead constituted contributory negligence. This highlights the threshold for unreasonable behaviour, which must be very high in order for it to break the chain of causation, and that where it falls short, the court will reduce damages based on contributory negligence. This distinction highlights that it is not enough for the claimant to be partially responsible, as they would need to have acted very unreasonably.
External Factors and Novus Actus Interveniens
External factors, such as natural events, can also be considered as a novus actus interveniens if they are deemed to be unforeseeable and independent of the initial wrongdoer's conduct. In Carslogie Steamship Co Ltd v Royal Norwegian Government [1952], a ship was damaged in a collision due to the defendant’s negligence and underwent temporary repairs. Subsequently, the ship was further damaged by stormy weather whilst sailing to New York. The court held that while the defendant was responsible for the initial damage caused by the collision, they were not responsible for the additional damage caused by the storm. The storm was determined to be a novus actus interveniens that broke the chain of causation. This position shows that not every intervening event will break the chain, but it is where an unforeseen natural event occurs that is so overwhelming that it supersedes the initial act. Similarly, in Southern Water Authority v Pegrum [1989], the court determined that while a blocked drain and unusually heavy rain contributed to a pollution event, these events were not of such an overpowering nature as to be a novus actus interveniens and the defendants were liable. In this case it was deemed that, although the rain and blocked drain contributed, it was the defendants’ own conduct that had caused the resulting damage and they could not use “Act of God” as a defence.
Foreseeability and Remoteness in Causation
The principle of novus actus interveniens is closely linked to the concepts of foreseeability and remoteness in legal reasoning. For an intervening act to be considered a valid break in the chain, it must generally be unforeseeable. In Knightley v Johns [1982] a negligent driver crashed his car near the exit of a tunnel, and at the scene a police officer ordered another officer to ride down the one way tunnel on his motorcycle to block the road, where he was involved in a collision. It was found that this action broke the chain of causation. The court held that it was not foreseeable that a police officer would act negligently, therefore that action was a novus actus interveniens. However, if the intervening act is a foreseeable consequence of the defendant’s initial conduct, the chain of causation is less likely to be broken. This demonstrates that while many actions will be foreseeable, the threshold for a negligent act is much higher as these are less likely to be deemed reasonably foreseeable.
The 'Eggshell Skull' Rule and Pre-Existing Conditions
The eggshell skull rule has an effect on the application of novus actus interveniens, particularly when the victim has a pre-existing vulnerability. The rule dictates that a defendant must take their victim as they find them, which includes both physical conditions, such as in Baker v Willoughby [1970], and also psychological or religious beliefs as is demonstrated in R v Blaue [1975]. In the Blaue case the victim refused a blood transfusion due to her religious convictions, which ultimately led to her death following a stabbing attack by the defendant. The court held that the defendant was still liable for the death because the refusal of treatment, though a voluntary act of the victim, did not break the chain of causation. This emphasizes that pre-existing conditions, including beliefs or vulnerabilities of a victim, do not operate as a novus actus interveniens if they are triggered or revealed by the defendant's initial action. The defendant must take their victim as they find them, including any pre-existing physical or mental vulnerabilities, meaning that even where the victims response to the initial actions was unexpected, this would not be sufficient to break the chain of causation.
Conclusion
Novus actus interveniens provides a mechanism to assess legal responsibility by evaluating the impact of intervening acts on the chain of causation, illustrating the legal system's careful approach to defining where culpability should rest. The principle hinges on demonstrating a voluntary and unforeseeable intervening act that effectively severs the causal connection between the defendant’s initial action and the resulting harm. Key cases like R v Kennedy, R v Pagett, and McKew v Holland and Hannen exemplify the practical application of this principle, showing that while voluntary acts can break the chain, reasonable acts taken in self-preservation or in response to duty often do not. Natural events may also operate as a novus actus interveniens when they are unforeseeable and independent. This principle is complicated by the ‘eggshell skull’ rule, which states that a tortfeasor takes their victim as they find them, and that this includes pre-existing conditions and beliefs, therefore not being a novus actus interveniens. Novus actus interveniens continues to provide a framework that acknowledges that an initial act may not always be the cause of resulting harm if a sufficiently distinct and independent cause intervenes. In complex scenarios, these legal analyses demonstrate a careful consideration of not only what caused harm, but who should bear responsibility for it.
