Learning Outcomes
This article examines the principles of causation in negligence, covering both factual and legal causation, the 'but for' test and its exceptions, the material contribution to harm and material increase in risk approaches, remoteness of damage, and the impact of intervening acts (novus actus interveniens) on breaking the chain of causation. It outlines the distinction between cumulative and alternative causal mechanisms, the difference between divisible and indivisible injuries and the consequences for apportionment and joint and several liability, the orthodox limits on loss of chance in negligence, and assessment of whether intervening acts break the chain, including claims involving subsequent medical treatment or claimant conduct.
SQE1 Syllabus
For SQE1, you are required to understand how causation links a defendant's breach of duty to the claimant's loss in negligence claims, including the application of rules for both factual and legal causation, especially in complex situations involving multiple potential causes or successive injuries, with a focus on the following syllabus points:
- The 'but for' test for factual causation and its application.
- Exceptions to the 'but for' test, such as the material contribution test (Bonnington Castings) and the material increase in risk approach (Fairchild).
- Cumulative vs alternative causes and proof difficulties (e.g., Wilsher v Essex AHA).
- The distinction between divisible and indivisible injuries in the context of multiple causes, and the implications for apportionment vs joint and several liability.
- The concept of legal causation, including remoteness of damage (The Wagon Mound) and the 'egg-shell skull' rule.
- Identifying intervening acts (novus actus interveniens) and determining if they break the chain of causation, including acts by claimants, third parties, and natural events.
- The effect of multiple sufficient causes and consecutive torts (Performance Cars, Baker v Willoughby; contrasted with Jobling).
- The orthodox approach to loss of chance in negligence (Hotson; Gregg v Scott), and the limited role of exceptional decisions.
Test Your Knowledge
Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.
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What is the primary test for establishing factual causation in negligence?
- The material contribution test.
- The 'but for' test.
- The foreseeability test.
- The proximity test.
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In which case was the principle established that a defendant could be liable if their breach materially contributed to the claimant's harm, even if it wasn't the sole cause?
- Barnett v Chelsea and Kensington Hospital Management Committee
- The Wagon Mound (No 1)
- Bonnington Castings Ltd v Wardlaw
- Baker v Willoughby
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True or False: The 'egg-shell skull' rule means a defendant is only liable for harm that was reasonably foreseeable, regardless of the claimant's pre-existing vulnerabilities.
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What legal principle determines whether harm suffered by a claimant is too far removed from the defendant's breach to be recoverable?
- Factual causation.
- Novus actus interveniens.
- Remoteness of damage (legal causation).
- Contributory negligence.
Introduction
Establishing that a defendant owed a duty of care and subsequently breached that duty is only part of a successful negligence claim. The claimant must also demonstrate that the defendant's breach caused the damage suffered. Causation acts as the essential link connecting the defendant's wrongful act to the claimant's harm. This involves satisfying tests for both factual causation (cause in fact) and legal causation (remoteness). This article explores these elements, particularly focusing on complexities arising from multiple causes and multiple injuries. These complexities frequently arise where there is cumulative exposure over time, successive torts or non-tortious vicissitudes, or scientific uncertainty about mechanisms of injury.
Key Term: Factual Causation
The principle that the defendant's breach of duty was, as a matter of fact, a necessary condition for the claimant's harm occurring.
Factual Causation: The 'But For' Test
The starting point for determining factual causation is the 'but for' test. The court asks: 'But for the defendant's negligence, would the claimant have suffered the harm?' If the answer is 'no' (the harm would not have occurred without the defendant's breach), then factual causation is typically established.
Worked Example 1.1
Ahmed attends hospital complaining of severe chest pains. Dr. Singh, the attending doctor, negligently fails to examine him properly and sends him home, advising rest. Ahmed suffers a fatal heart attack hours later. Medical evidence shows that even with prompt and correct treatment, Ahmed's condition was so advanced that he would have died regardless. Has Dr. Singh's negligence caused Ahmed's death?
Answer:
No. Applying the 'but for' test, Ahmed would have died even if Dr. Singh had not been negligent. Therefore, Dr. Singh's breach did not cause the death. (Based on Barnett v Chelsea and Kensington Hospital Management Committee [1969]).
The ‘but for’ test is the default approach in straightforward, single-cause cases. However, it must be applied alongside the principle that a defendant is only liable for loss within the scope of the duty they owed; this avoids attributing liability for losses unconnected to the risk that made the conduct negligent.
Problems with the 'But For' Test
The 'but for' test can be difficult to apply where there are multiple potential causes of the claimant's harm. If there are several independent factors, any one of which could have caused the harm, it may be impossible to prove on the balance of probabilities that any single breach was the decisive cause. This can leave claimants without a remedy despite clear wrongdoing, so the courts have developed responses for specific categories of cases.
Multiple Potential Causes
Where multiple factors contribute to the claimant's harm, especially in cases involving cumulative exposure or scientific uncertainty, the courts have developed alternative approaches to the 'but for' test. A key distinction is between:
- cumulative causes that together produce an injury (e.g., cumulative dust exposure leading to pneumoconiosis), and
- alternative causes where any one of several different factors could alone have caused the outcome (e.g., five distinct possible causes of a premature baby’s blindness).
Both categories raise proof problems, but they are treated differently.
Material Contribution to Harm
If the defendant's breach can be shown to have made a 'material contribution' to the claimant's harm, this may be sufficient to establish factual causation, even if the breach was not the sole cause. This test often applies where the harm results from cumulative noxious exposure from both tortious and non-tortious sources, or where multiple factors operate together.
Key Term: Material Contribution to Harm
Where the defendant's breach made a more than negligible contribution to the claimant's injury, causation may be established even if the 'but for' test is not satisfied.
In Bonnington Castings Ltd v Wardlaw [1956], a factory worker developed pneumoconiosis from inhaling silica dust. Some dust exposure was non-tortious ('innocent dust'), while some resulted from the employer's breach ('guilty dust'). The House of Lords held that because the 'guilty dust' had materially contributed to the disease, the employer was liable.
The approach has also been applied in clinical settings where negligent and non-negligent factors cumulatively weaken a patient, resulting in indivisible injury. In such cases, liability arises if the negligent factor materially contributed to the overall harm, even if precise attribution of proportions is impossible, provided the injury itself is treated as indivisible.
Worked Example 1.2
A patient suffers hypoxic brain damage after a prolonged period of weakness caused partly by negligent post-operative care and partly by a non-negligent medical condition. The medical experts cannot apportion precisely how much each factor contributed. Is causation established?
Answer:
Yes. Where negligent and non-negligent factors cumulatively cause an indivisible injury, showing that negligence made a more than negligible contribution can suffice. The defendant is liable for the whole injury on the material contribution to harm approach.
Material Increase in Risk
In exceptional cases involving scientific uncertainty (particularly mesothelioma caused by asbestos exposure), the courts have held that factual causation can be established if the defendant's breach materially increased the risk of the claimant suffering the harm.
In Fairchild v Glenhaven Funeral Services Ltd [2002], the claimants developed mesothelioma after being exposed to asbestos by several different employers over different periods. It was impossible to determine which exposure caused the fatal illness. The House of Lords held that each employer who had negligently exposed the claimant to asbestos, thereby materially increasing the risk of mesothelioma, could be held liable. This approach ensures claimants are not left without remedy due to evidential gaps caused by scientific uncertainty.
Key Term: Material Increase in Risk
In specific circumstances (e.g., mesothelioma), proof that the defendant's breach materially increased the risk of the claimant contracting the disease can establish factual causation.
Subsequent case law confirms two important points. First, the risk-based approach applies even where there is a single negligent source of exposure and only background environmental exposure otherwise (Sienkiewicz v Greif). Second, Parliament has ensured that in mesothelioma cases, any responsible defendant can be held liable for the whole indivisible injury, even if other employers are insolvent; s. 3 of the Compensation Act 2006 restores joint and several liability in such cases. For other asbestos diseases such as lung cancer (where the Fairchild exception does not apply), liability will generally be apportioned between defendants according to their contribution to risk consistent with Barker v Corus.
Exam Warning The Fairchild principle, imposing joint and several liability for materially increasing the risk of mesothelioma, was specifically restored for mesothelioma claims by s. 3 Compensation Act 2006, overriding the apportionment approach suggested in Barker v Corus UK Ltd [2006]. For other conditions, the common law principles around material contribution apply. Be precise about the type of harm alleged in the question.
Alternative Causes and Scientific Uncertainty
Where there are several different possible causal mechanisms, only one of which involves negligence, and medical science cannot say which actually caused the harm, the material risk approach is confined largely to mesothelioma. In other non-mesothelioma settings, the claimant must still satisfy the balance of probabilities that the negligent cause was the actual cause.
Worked Example 1.3
A premature baby develops blindness. There are five distinct potential causes, only one of which is a negligent excess of oxygen administration. Medicine cannot say which cause operated on the balance of probabilities. Is the hospital liable?
Answer:
No. Where multiple distinct potential causes exist and science cannot identify which operated, the claimant will generally fail on causation (the Fairchild exception does not apply). The negligent cause is not proved, on balance, to have caused the injury.
Divisible vs. Indivisible Injuries
When multiple causes are involved, the nature of the injury is important:
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Divisible Injury: An injury that can be attributed incrementally to different exposures or causes (e.g., industrial deafness, where severity relates to cumulative exposure). Liability may be apportioned between defendants based on their contribution.
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Indivisible Injury: An injury that cannot be broken down into parts attributable to specific causes (e.g., mesothelioma, which can be triggered by a single fibre, or a single broken leg in a multi-car collision). Where multiple defendants contribute to an indivisible injury, they are typically held jointly and severally liable, meaning the claimant can recover the full amount from any one defendant.
Key Term: Divisible Injury
Harm whose severity can be apportioned between multiple causes, allowing damages to be divided according to each cause’s contribution.Key Term: Indivisible Injury
Harm that is not amenable to rational apportionment because it is a single whole; defendants jointly causing such harm are usually jointly and severally liable.
Divisible versus indivisible classification determines whether the court apportions damages or imposes full joint and several liability. Industrial disease claims often present divisible injuries; mesothelioma is treated as indivisible. For asbestos-related lung cancer, damages may be apportioned where supported by evidence of varying contributions to risk over time.
Worked Example 1.4
A factory worker suffers gradual industrial deafness after noise exposure over 20 years with three employers, two negligent and one non-negligent. How will damages be addressed?
Answer:
Industrial deafness is typically divisible. The negligent employers are liable to the extent each contributed to the cumulative noise exposure. The non-negligent employer is not liable, and damages are apportioned between the negligent employers.
Legal Causation: Remoteness and Intervening Acts
Even if factual causation is established, the claimant must also demonstrate legal causation. This involves two key aspects: remoteness of damage and the absence of any intervening act breaking the chain of causation.
Remoteness of Damage
The defendant is only liable for damage that is of a reasonably foreseeable type as a consequence of their breach. This principle, established in Overseas Tankship (UK) Ltd v Morts Dock and Engineering Co Ltd (The Wagon Mound (No 1)) [1961], prevents liability extending to harms that are too remote.
Key Term: Remoteness of Damage
A legal principle limiting liability to types of harm that were reasonably foreseeable consequences of the defendant's breach of duty.
The extent or manner in which the foreseeable type of harm occurs need not be foreseeable. If the type of harm is foreseeable, the defendant is liable for the full extent of that harm, subject to the egg-shell skull rule.
Worked Example 1.5
Workers negligently allow oil to spill from a ship into a harbour. The oil spreads to a nearby wharf where welding is taking place. Sparks ignite debris floating on the oil, causing a large fire that damages the wharf. Evidence showed it was not foreseeable that furnace oil floating on water could ignite in this way. Is the damage to the wharf too remote?
Answer:
Yes. Applying the test from The Wagon Mound (No 1), the fire damage was not a reasonably foreseeable type of consequence of the oil spill. Although some damage from fouling was foreseeable, fire damage was considered too remote.
The 'Egg-Shell Skull' Rule
An exception to the foreseeability test for remoteness is the 'egg-shell skull' (or 'thin skull') rule. This rule states that the defendant must take their victim as they find them. If the claimant has a particular vulnerability that makes their injury more severe than would have been reasonably foreseeable, the defendant is liable for the full extent of the harm suffered.
Key Term: Egg-Shell Skull Rule
The principle that a defendant is liable for the full extent of the harm suffered by a claimant, even if the severity is due to the claimant's pre-existing vulnerability and was unforeseeable.
This applies to both physical and psychiatric vulnerability. It also extends to certain financial vulnerabilities in specific contexts, such as when a claimant’s impecuniosity reasonably increases the cost of mitigation.
Worked Example 1.6
A worker suffers a minor burn on his lip due to his employer's negligence. The burn triggers a pre-existing cancerous condition, leading to the worker's death. Is the employer liable for the death, even if cancer developing from such a burn was unforeseeable?
Answer:
Yes. As long as the initial type of injury (the burn) was foreseeable, the defendant is liable for the full consequences, including the unforeseeably severe outcome due to the claimant's pre-existing vulnerability. (Based on Smith v Leech Brain & Co Ltd [1962]).
Intervening Acts (Novus Actus Interveniens)
An intervening act or event occurring after the defendant's breach but before the claimant suffers the damage may break the chain of causation, relieving the defendant of liability for the subsequent harm.
Key Term: Novus Actus Interveniens
A new intervening act (by the claimant, a third party, or a natural event) that breaks the chain of causation between the defendant's breach and the claimant's ultimate harm.
- Act of the Claimant: If the claimant acts unreasonably following the defendant's breach, their actions may break the chain of causation (McKew v Holland & Hannen & Cubitts (Scotland) Ltd [1969]). The threshold is high; mere carelessness tends to sound in contributory negligence rather than breaking the chain.
- Act of a Third Party: An act by a third party will generally break the chain if it was unforeseeable and independent of the defendant’s breach. Negligent medical treatment following an injury caused by the defendant is unlikely to break the chain unless it is grossly negligent.
- Natural Event: An unforeseeable natural event occurring after the breach may break the chain.
Where multiple wrongdoers contribute to a final loss, courts may analyse the overall damage and attribute responsibility without necessarily finding a break in causation, especially when successive negligent acts contribute to the ultimate condition.
Worked Example 1.7
A driver negligently causes a collision. The claimant suffers a leg fracture. During hospital treatment, a doctor makes a negligent error that worsens the injury. Does the doctor’s negligence break the chain, absolving the driver of liability for the worsened condition?
Answer:
Generally, no. Negligent medical treatment is a foreseeable consequence of personal injury and usually does not break the chain unless it is so grossly negligent as to be entirely independent. The original tortfeasor remains liable for the full extent of the injury as it unfolds, subject to any contribution claim between defendants.
Multiple Sufficient Causes
Where two separate tortious acts occur consecutively, both contributing to the claimant's loss, complex questions arise.
- In Baker v Willoughby [1970], the claimant suffered a leg injury due to the defendant's negligence. Before the trial, he was shot in the same leg during a robbery, requiring amputation. The House of Lords held the original defendant remained liable for the ongoing effects of the initial injury, reasoning that the second tort did not erase the loss caused by the first.
- In Performance Cars Ltd v Abraham [1962], a Rolls-Royce requiring a respray due to an initial collision was then involved in a second collision also necessitating a respray. The second defendant was not liable because there was no additional loss; the car already required the respray.
- In Jobling v Associated Dairies Ltd [1982], the claimant suffered a back injury at work due to the employer's negligence. Later, he developed an unrelated spinal disease rendering him unfit for work. The House of Lords held the employer's liability ceased when the unrelated disease took effect, treating the disease as a vicissitude of life that obliterated the continuing loss from the earlier tort.
These decisions reflect different approaches depending on whether the second event is a further tort (no reduction of the first defendant’s liability) or a non-tortious vicissitude that would have occurred anyway (limiting the earlier tortfeasor’s liability).
Worked Example 1.8
C negligently injures D’s back, causing a 50% loss of earning capacity. Two years later, before trial, D develops an unrelated degenerative spinal disease that would have occurred in any event and now prevents any work. How is C’s liability measured?
Answer:
C is liable only up to the point when the supervening non-tortious disease takes effect. The later vicissitude limits continuing loss flowing from the initial tort (consistent with Jobling).
Loss of Chance
Factual causation in negligence generally adopts an all-or-nothing approach on the balance of probabilities. Where the claimant’s case is that the defendant’s negligence merely reduced their chances of a better outcome (e.g., successful treatment), and the pre-negligence chance was below 50%, the claim typically fails.
Key Term: Loss of Chance
In negligence, a claim that the defendant’s breach reduced the likelihood of a favourable outcome; generally not recoverable unless the claimant proves, on balance, that the breach caused the injury.
In Hotson v East Berkshire Health Authority, a child’s condition would on the evidence likely have developed even with proper treatment (a 75% non-negligent chance of the bad outcome). The lost 25% chance was not enough; causation failed. In Gregg v Scott, a negligent delay reduced a cancer patient’s ten‑year survival chance from 42% to 25%. The claim failed because survival was not probable before the negligence. The courts have resisted converting clinical negligence into claims for probabilistic loss of chance.
Worked Example 1.9
A patient had a 30% chance of avoiding paralysis with timely diagnosis. Due to a negligent delay, the chance fell to 10% and paralysis ensued. Can the patient recover for a 20% lost chance?
Answer:
No. The courts require proof on the balance of probabilities that negligence caused the injury. A pre-existing chance below 50% is insufficient to establish causation in negligence by reference only to ‘lost chance’.
Further applications and clarifications
Cumulative vs alternative causes in practice
- Cumulative causes (e.g., guilty dust plus innocent dust) are amenable to the material contribution to harm approach.
- Alternative causes (e.g., several distinct potential causes, only one negligent) typically require proof that the negligent cause actually operated; the material risk approach is largely confined to mesothelioma.
Apportionment and insurance
Where apportionment is appropriate (divisible injuries), each defendant is liable for the extent to which they contributed. In indivisible injury cases, defendants may be jointly and severally liable. Apportionment rules and insurance allocation have been considered in asbestos litigation; mesothelioma remains governed by statute and special common law rules.
Revision Tip
Distinguishing Baker and Jobling is fundamental. Baker involved two consecutive tortious acts, while Jobling involved a tort followed by a supervening non-tortious illness. The courts approach these scenarios differently, focusing on whether the second event removes the damage caused by the first tortious act.
Key Point Checklist
This article has covered the following key knowledge points:
- Causation in negligence requires proof of both factual causation and legal causation (remoteness).
- The primary test for factual causation is the 'but for' test: 'But for' the defendant's breach, would the harm have occurred?
- Where the 'but for' test is difficult to apply due to cumulative causes, the 'material contribution to harm' test (Bonnington Castings) may establish factual causation if the breach made a more than negligible contribution.
- In exceptional cases of scientific uncertainty concerning mesothelioma, demonstrating a 'material increase in risk' (Fairchild) can establish factual causation; s. 3 Compensation Act 2006 restores joint and several liability for mesothelioma.
- Distinguish cumulative from alternative causes; the risk-based approach is not a general substitute for proof of causation in non-mesothelioma cases.
- Divisible injuries allow apportionment by contribution; indivisible injuries usually result in joint and several liability among concurrent tortfeasors.
- Legal causation (remoteness) limits liability to damage of a reasonably foreseeable type (The Wagon Mound (No 1)), but the extent and manner of harm need not be foreseeable.
- The 'egg-shell skull' rule makes defendants liable for the full extent of harm, even if unforeseeably severe due to the claimant's vulnerability; it can also apply to certain financial vulnerabilities.
- A novus actus interveniens by the claimant, a third party, or nature can break the chain of causation if it is sufficiently independent and unforeseeable; ordinary negligent medical treatment rarely does so.
- Cases involving consecutive causes (Performance Cars, Baker, Jobling) require careful analysis of whether the second event is a tort or a vicissitude of life.
- Loss of chance claims typically fail in negligence unless the claimant proves, on the balance of probabilities, that the breach caused the injury (e.g., Hotson; Gregg v Scott).
Key Terms and Concepts
- Factual Causation
- Material Contribution to Harm
- Material Increase in Risk
- Divisible Injury
- Indivisible Injury
- Remoteness of Damage
- Egg-Shell Skull Rule
- Novus Actus Interveniens
- Loss of Chance