Define: Causation

Quick Summary of Causation

Causation is the relationship between an activity and the outcome. Claimants who wish to file a personal injury claim must demonstrate that the defendant’s actions were the “proximate cause” for their loss. Causation involves proving the person new the outcome was likely or could be the foreseeable result of the negligence and continued to proceed with the action, exposing another party to the risk of harm.

For example, if a driver rams their car into a restaurant and the ceiling of the restaurant collapses and a steel beam crushes a patron of the restaurant, injuring him, the patron may sue the driver for their injuries. Although the driver did not intentionally drop the steel beam on the patron they should have foreseen that their actions were the proximate cause of the patron’s injury because injury to a patron of the restaurant is a foreseeable result of crashing a car into a building. Note that the particular injury and the manner in which the injury occurs do not have to be foreseeable in order to constitute proximate cause. Talk to an injury lawyer if you are considering filing an injury claim and you are not sure if your case meets the requirements.

Causation is the bringing about of a result, and in law, it is an element in various tests for legal liability. Most tests for legal liability in criminal and civil law require the defendant to have ‘caused’ the result of which the plaintiff complains. For example:

• Homicide (criminal law): requires that the accused have caused the victim’s death
• Negligence (civil law): requires that the defendant have caused the harm that befell the plaintiff
• Breach of contract (civil law): requires that the defendant’s breach have caused the plaintiff’s loss.

If the plaintiff/prosecution cannot establish the causal link between the defendant’s act and the plaintiff/victim’s harm, then liability will not be established.

Background Concepts

Most legal systems are, to a greater or lesser extent, concerned with the notions of fairness and justice. If a state is going to penalise a person or require that person to pay compensation to another for losses incurred, this imposition of liability will be derived from the idea that those who injure others should take responsibility for their actions. Although some parts of any legal system will have qualities of strict liability, most look to establish liability by showing that the defendant was the cause (applying various legal tests in order to establish this) of the particular injury or loss.

Even the youngest children quickly learn that, with varying degrees of probability, consequences flow from physical acts and omissions. The more predictable the outcome, the greater the likelihood that the actor caused the injury or loss intentionally. There are many ways in which the law might capture this simple rule of practical experience: that there is a natural flow to events, that a reasonable man in the same situation would have foreseen this consequence as likely to occur, that the loss flowed naturally from the breach of contractual or tortious duty, etc. However it is phrased, the essence of the degree of fault attributed will lie in the fact that reasonable people try to avoid injuring others, so if harm was foreseeable, there should be liability to the extent that the extent of the harm actually resulting was foreseeable.

The Relationship Between Causation And Liability

The causality of an event by itself is not sufficient to create legal liability.

Sometimes causation is one part of a multi-stage test for legal liability.

For example, for the defendant to be held liable for the tort of negligence, the defendant must have

1. owed the plaintiff a duty of care;
2. breached that duty;
3. by so doing causing damage to the plaintiff; and
4. that damage must not have been too remote.

Causation is but one component of the tort.

On other occasions, causation is the only requirement for legal liability (other than the fact that the outcome is proscribed). For example, in the law of product liability, the fact that the defendant’s product caused the plaintiff harm is the only thing that matters. The defendant need not also have been negligent.

On other occasions, causation is irrelevant to legal liability altogether. For example, under a contract of indemnity insurance, the insurer agrees to indemnify the victim for harm not caused by the insurer but by other parties.

Because of the difficulty in establishing causation, it is one area of the law where the case law overlaps significantly with general doctrines of analytic philosophy to do with causation. The two subjects have long been somewhat intermingled.

Establishing Causation

Where establishing causation is required to establish legal liability, it is usually said that it involves a two-stage inquiry.

The first stage involves establishing ‘factual’ causation. Did the defendant’s act, in fact, cause the plaintiff’s loss?

The second stage involves establishing ‘legal’ causation. This is often a question of public policy: is this the sort of situation in which, despite the outcome of the factual enquiry, we might nevertheless release the defendant from liability or impose liability?

Establishing Factual Causation

The usual method of establishing factual causation is the ‘but for’ test. The but for test enquires, ‘But for the defendant’s act, would the harm have occurred?’ A shoots and wounds B. We ask, ‘But for A’s act, would B have been wounded?’ The answer is ‘no’. So we conclude that A caused the harm to B. The but-for test is a test of necessity. It asks whether it was ‘necessary’ for the defendant’s act to have occurred for the harm to have occurred.

The but-for test often gives us the right answer to causal problems, but sometimes not. Two difficulties are immediately obvious. The first is that under the but-for test, almost anything is a cause. But for a tortfeasor’s grandmother’s birth, the relevant tortious conduct would not have occurred. But for the victim of a crime missing the bus, he or she would not have been at the site of the crime, and hence the crime would not have occurred. Yet in these two cases, the grandmother’s birth or the victim’s missing the bus are not intuitively ’causes’ of the resulting harm. This often does not matter in the case where cause is only one element of liability, as the remote actor will most likely not have committed the other elements of the test. However, this situation can arise in strict liability situations.

The other problem is that of overdetermination. Imagine two hunters, A and B, who each negligently fire a shot that takes out C’s eye. Each shot on its own would have been sufficient to cause the damage. But for A’s shot, would C’s eye have been taken out? Yes. The same answer follows in relation to B’s shot. But on the ‘but for’ test, this leads us to the counterintuitive position that neither shot caused the injury.

The courts have generally accepted the but for test notwithstanding these weaknesses, qualifying it by saying that causation is to be understood ‘as the man in the street’ would: Yorkshire Dale Steamship Co v Minister of War Transport [1942] AC 691 (House of Lords) or by supplementing it with ‘common sense’: March v Stramare (1991) 171 CLR 506 (High Court of Australia).

However, legal scholars have attempted to make further inroads into what explains these difficult cases. Some scholars have proposed a test of sufficiency instead of a test of necessity. H. L. A. Hart, Tony Honoré, and later Richard Wright have said that something is a cause if it is a ‘necessary element of a set of conditions jointly sufficient for the result’. This is known as the NESS test. In the case of the two hunters, the ‘set’ of conditions required to bring about the result of the victim’s injury would include a gunshot to the eye, the victim being in the right place at the right time, gravity, etc. In such a set, either of the hunters’ shots would be a member, and hence a cause. This arguably gives us a more theoretically satisfying reason to conclude that something was the cause of something else than by appealing to notions of intuition or common sense.

Hart and Honore, in their famous work Causation in the Law, also tackle the problem of ‘too many causes’. For them, there are degrees of causal contribution. A member of the NESS set has a “causally relevant condition. This is elevated to “cause,” where it is a deliberate human intervention or an abnormal act in the context. So, returning to our hunter example, hunter A’s grandmother’s birth is a causally relevant condition but not a “cause”. On the other hand, hunter A’s gunshot, being a deliberate human intervention in the ordinary state of affairs, is elevated to the status of “cause”. An intermediate position can be occupied by those who “occasion” harm, such as accomplices. Imagine an accomplice to a murder who drives the principal to the scene of the crime. Clearly, the principal’s act in committing the murder is “cause” (on the but for or NESS test). So is the accomplice’s act in driving the principal to the scene of the crime. However, the causal contribution is not of the same level (and, incidentally, this provides some basis for treating principals and accomplices differently under criminal law). Leon Green and Jane Stapleton are two scholars who take the opposite view. They consider that once something is a “but for” (Green) or NESS (Stapleton) condition, that ends the factual inquiry altogether, and anything further is a question of policy.

Establishing Legal Causation

Notwithstanding the fact that causation may be established in the above situations, the law often intervenes and says that it will nevertheless not hold the defendant liable because, in the circumstances, the defendant is not to be understood, in a legal sense, as having caused the loss. In the USA, this is known as the doctrine of Proximate cause. The most important doctrine is that of ‘novus actus interveniens’, which means a ‘new intervening act’ which may ‘cut the chain of causation’.

Imagine the following:. A critically injures B. As B is wheeled to an ambulance, she is struck by lightning. She would not have been if she had not been injured in the first place. Clearly, then, A caused B’s whole injury on the ‘but for’ or NESS test. However, at law, the intervention of a supervening event renders the defendant not liable for the injury caused by the lightning.

The effect of the principle may be stated simply as follows:

if the new event, whether through human agency or natural causes, does not break the chain, the original actor is liable for all the consequences flowing naturally from the initial circumstances. But if the new act breaks the chain, the liability of the initial actor stops at that point, and the new actor, if human, will be liable for all that flows from his or her contribution.
This is usually expressed as a question of ‘foreseeability. An actor is liable for the foreseeable, but not the unforeseeable, consequences of his or her act. For example, it is foreseeable that if I shoot someone on a beach and they are immobilised, they may drown in a rising tide rather than from the gunshot wound or blood loss. However, it is not (generally speaking) foreseeable that they will be struck by lightning and killed by that event.

This type of causal foreseeability is to be distinguished from foreseeability of extent or kind of injury, which is a question of remoteness of damage, not causation. For example, if I conduct welding work on a dock that lights an oil slick that destroys a ship a long way down the river, it would be hard to construe my negligence as anything other than the cause of the ship’s damage. There is no novus actus interveniens. However, I may not be held liable if that damage is not of a type foreseeable as arising from my negligence: The Waggon Mound (No. 1) [1961] AC 388 (Privy Council). That is a question of public policy, not one of causation.

Other Relevant Considerations

Because causation in the law is a complex amalgam of fact and policy, other doctrines are also important, such as foreseeability and risk. Particularly in the United States, where the doctrine of ‘proximate cause’ effectively amalgamates the two-stage factual and legal causation inquiry favoured in the English system, one must always be alert to these considerations in assessing the postulated relationship between two events.

Foreseeability Test

Some aspects of the physical world are so inevitable that it is always reasonable to impute knowledge of their incidence. So if A abandons B on a beach, A must be taken to foresee that the tide comes in and goes out. But the mere fact that B subsequently drowns is not enough. A court would have to consider where the body was left and what level of injury A believed that B had suffered. If B was left in a position that any reasonable person would consider safe but a storm surge caused extensive flooding throughout the area, this might be a novus actus. It is not necessary for a court to rule that every incident falling within a foreseen class is a natural link in the chain just because B sustained additional harm as a result of an event within that class. Only those causes that are reasonably foreseeable fit naturally into the chain. So if A had heard a weather forecast predicting a storm, the drowning would be a natural outcome. But if this was an event like a flash flood, an entirely unpredictable event, it would be a novus actus.

The question of A’s beliefs is no different. If A honestly believes that B is only slightly injured and so could move himself out of danger without difficulty, how fair is it to say that he ought to have foreseen? The test is what a reasonable person would have known and foreseen, given what A had done. It is the function of any court to evaluate behaviour. A defendant cannot evade responsibility through a form of wilful blindness. The fault lies not only in what a person actually believes but also in failing to understand what the vast majority of other people would have understood. Hence, the test is hybrid, looking both at what the defendant actually knew and foresaw (i.e., subjective) and at what a reasonable person would have known (i.e., objective), and then combining the conclusions into a general evaluation of the degree of fault or blameworthiness.

Similarly, in the quantification of damages generally and/or the partitioning of damages between two or more defendants, the extent of the liability to compensate the plaintiff(s) will be determined by what is reasonably foreseeable. So if, for example, the plaintiff unexpectedly contributed to the extent of the loss suffered, that additional element would not be included in the damages award, even though the plaintiff would not have had the opportunity to make this mistake had it not been for the defendant’s breach. In cases involving the partitioning of damages between multiple defendants, each will be liable to the extent that their contribution foreseeably produced the loss.

Risk

Sometimes the reverse situation to a novus actus occurs, i.e. factual causation cannot be proved but the court nevertheless does want to hold the defendant liable. In Sindell v. Abbott Laboratories, 607 P.2d 924 (1980), the plaintiff consumed medication that caused bodily injury due to its negligent manufacture. However, there were many manufacturers of that drug in the market. The manufacturer of the particular medication that caused the injury could not be ascertained for certain. In that situation, the court held that the defendant was to be held liable proportionately to its market share. This departs from traditional notions of pure cause to adopt a ‘risk-based’ approach to liability. The defendant was held liable because of the amount of risk it contributed to the occurrence of the harm. Note that a risk theory is not strictly a theory built on notions of cause at all, as, by definition, the person who caused the injury could not be ascertained for certain. However, it does show that legal notions of causation are a complex mixture of factual causes and ideas of public policy relating to the availability of legal remedies. In R. V. Miller, the House of Lords said that a person who puts a person in a dangerous position will be criminally liable if he does not adequately rectify the situation.

Evidence Proving Causation

To be acceptable, any rule of law must be capable of being applied consistently so a definition of the criteria for this qualitative analysis must be supplied. Let us assume a purely factual analysis as a starting point. A injures B and leaves him lying in the road. C is a driver who fails to see B on the road and, by running over him, contributes to the cause of his death. It would be possible to ask for a detailed medical evaluation at a post mortem to determine the initial degree of injury and the extent to which B’s life was threatened, followed by a second set of injuries from the collision and their contribution. If the first incident merely damaged B’s leg so that he could not move, it is tempting to assert that C’s driving must have been the more substantial cause and so represents a novus actus breaking the chain. Equally, if B was bleeding to death and the only contribution that the driving made was to break B’s arm, the driving is not a novus actus and does not break the chain. But this approach ignores the issue of A’s foresight.

Roads are, by their nature, used by vehicles, and it is clearly foreseeable that a person left lying on the road is at risk of being further injured by an inattentive driver. Hence, if A leaves B on the road with knowledge of that risk and the foreseen event occurs, A remains the more proximate cause. This leaves the question of whether the test of foresight should be subjective, objective, or hybrid (i.e., both subjective and objective). Obviously, there is no difficulty in holding A liable if A had actual knowledge of the likelihood that B would be further injured by a driver. The fault that caused the initial injury is compounded by the omission to move B to a safer place or call for assistance. But let us assume that A never refers to the possibility of further injury. The issue is now the extent to which knowledge may be imputed objectively.

The Future?

A difficult issue that has arisen recently is the case where the defendant neither factually causes the harm nor increases the risk of its occurrence. In Chester v. Afshar [2004] 4 All ER 587 (House of Lords), a doctor negligently failed to warn a patient of the risks inherent in an operation. The patient had the operation, and a risk materialised, causing injury. It was found that even if the patient had been warned, the patient would still have undergone the operation, simply at a different time. The risk of injury would be the same at both times. Accordingly, the doctor neither caused the injury (because but for the failure to warn, the patient would still have gone ahead with the operation) nor increased the risk of its occurrence (because the risk was the same either way). Yet the House of Lords, embracing a more normative approach to causation, still held the doctor liable. Lawyers and philosophers continue to debate whether and how this changes the state of the law.

English Criminal Case Law Examples

Novus actus interveniens

• Victim’s contribution R v Dear (1996) CLR 595. Believing that the victim had sexually interfered with his 12-year-old daughter, the defendant attacked the victim with a Stanley knife. The defendant argued that the chain of causation had been broken because, two days later, the victim had committed suicide either by reopening his wounds or because he had failed to take steps to staunch the blood flow after the wounds had reopened spontaneously (i.e. the potential suicide constituted a novus actus interveniens). It was held that the real question was whether the injuries inflicted by the defendant were an operating and significant cause of or contribution to the death. Distinctions between the victim’s mere self-neglect (no break in the chain) and the victim’s gross self-neglect (break in the chain) were not helpful. The victim’s death resulted from bleeding from the artery severed by the defendant. Whether the resumption or continuation of that bleeding was deliberately caused by the victim, the defendant’s conduct remained the operative and significant cause of the victim’s death.
• third party’s inadvertent contribution R v Smith (1959) In 2 QB 35, the defendant stabbed his victim twice in a barracks room brawl. Another soldier carried him to the medical centre but dropped him twice. The medical captain was very busy and failed to recognise the extent of the injuries. If the soldier had received proper treatment, he would have had a good chance of a complete recovery. Smith was convicted of manslaughter because the wound was the “operating and substantial cause of death. In R v Cheshire (1991), 3 AER 670, the victim was shot in the leg and stomach. In the hospital, he suffered pneumonia and respiratory problems in intensive care, so he had a tracheotomy. After two months, he died. There was some medical negligence because the tracheotomy had caused a thickening of tissue, ultimately causing suffocation. In upholding the conviction for murder, Beldam LJ. laid down the following test:

Even though negligence in the treatment of the victim was the immediate cause of his death, the jury should not regard it as excluding the responsibility of the accused unless the negligent treatment was so independent of his acts and in itself so potent in causing death that they regard the contribution made by his acts as insignificant.

• Third party’s deliberate intervention R v Malcherek (1981) 73 Cr. App. R. 173. The victim was placed on a life support machine and, after determining that she was brain dead, the doctors turned off the machine. The defendant appealed the conviction of murder, arguing that the doctors had broken the chain of causation by deliberately switching off the life support machine. It was held that the original wounds were the operating and substantial cause of death and that a life support machine does no more than hold the effect of the injuries in suspension and when the machine is switched off, the original wounds continue to cause death no matter how long the victim survives after the machine’s disconnection. In R v Pagett (1983), 76 Cr. App. R. 279, to resist lawful arrest, the defendant held a girl in front of him as a shield and shot at armed policemen. The police instinctively fired back and killed the girl. The Court of Appeal held that the defendant’s act caused the death and that the reasonable actions of a third party acting in self-defence could not be regarded as a novus actus interveniens because self-defence is a foreseeable consequence of his action and had not broken the chain of causation.

Foreseeability

• Victim’s conscious actions R v. Blaue (1975) 61 Cr. App. R. 271 is a criminal law application of the “eggshell skull rule” in tort. The defendant visited the home of a Jehovah’s Witness and demanded sex. When she refused, he stabbed her four times. At the hospital, she refused a blood transfusion, which would have saved her life. There was no suggestion that the doctors had acted improperly. Blaue was convicted of manslaughter by an unlawful act, namely wounding with intent. “But for” his actions, she would not have been faced with the choice about treatment and those who use violence on others must take their victims as they find them (albeit that he had known her religion and so her refusal was foreseeable).
• Victim’s inherent condition R v. Corbett (1996), CLR 594. The victim was a mentally handicapped 26-year-old man who had problems with high alcohol consumption. In an argument after drinking, the defendant attacked the victim. When running away, the victim fell into the gutter and was struck and killed by a passing car. The test was held to be whether what the victim did was within the range of foreseeability given the amount he had had to drink.

Disclaimer

This site contains general legal information but does not constitute professional legal advice for your particular situation. Persuing this glossary does not create an attorney-client or legal adviser relationship. If you have specific questions, please consult a qualified attorney licensed in your jurisdiction.

This glossary post was last updated: 9th April, 2024.