Learning Outcomes
This article examines the principles of factual causation in negligence, specifically addressing situations where multiple factors contribute to the claimant's loss. It explains the limitations of the standard 'but for' test and details the application of the 'material contribution' principle, encompassing both material contribution to harm and material increase in risk. Your understanding of these concepts, supported by key case law, will enable you to analyse complex causation scenarios in SQE1-style multiple-choice questions.
SQE1 Syllabus
For SQE1, you are required to understand the principles of causation as a key element in establishing negligence. This involves applying the rules relating to factual causation, particularly where multiple causes may be present. Your revision should focus on:
- The standard 'but for' test for factual causation and its limitations.
- The concept of multiple potential causes of harm.
- The principle of 'material contribution' to harm as an exception to the 'but for' test.
- The related principle of 'material increase in risk' and its application, particularly in cases of scientific uncertainty.
- Distinguishing between divisible and indivisible injuries in the context of multiple tortfeasors.
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.
-
In negligence, what is the standard test for establishing factual causation?
- The 'reasonable foreseeability' test.
- The 'material contribution' test.
- The 'but for' test.
- The 'balance of probabilities' test.
-
In which landmark case was the principle that a defendant could be liable for materially increasing the risk of harm established, particularly where scientific certainty on the precise cause was lacking?
- Barnett v Chelsea & Kensington Hospital Management Committee
- Bonnington Castings Ltd v Wardlaw
- McGhee v National Coal Board
- Wilsher v Essex Area Health Authority
-
The 'material contribution to harm' test is most applicable in which scenario?
- Where there is only one potential cause of the claimant's harm.
- Where the claimant's harm is caused by exposure to a single, identifiable source of danger attributable to the defendant.
- Where the claimant's harm results from the cumulative effect of multiple factors, at least one of which is due to the defendant's breach.
- Where the defendant's breach only creates a risk of harm, but causation cannot be definitively proven.
Introduction
Establishing causation is the essential third element in proving negligence, linking the defendant's breach of duty to the claimant's damage. Factual causation addresses whether the defendant's actions were, as a matter of fact, a cause of the claimant's loss. The primary method for determining this is the 'but for' test. However, this test proves inadequate in complex scenarios involving multiple potential causes of harm. In such situations, the courts have developed alternative approaches, notably the 'material contribution' tests, to ensure fairness and avoid denying claimants a remedy simply because the precise causal link is difficult to establish scientifically or evidentially. This article explores these principles, focusing on the 'material contribution' doctrine in the context of multiple causes.
Factual Causation: The 'But For' Test
The starting point for factual causation is the 'but for' test. You must ask: 'But for the defendant's breach of duty, 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 established. If the answer is 'yes' (the harm would have occurred anyway, regardless of the defendant's breach), then causation is not established, and the claim fails.
Key Term: Factual Causation The requirement that the claimant must prove, on the balance of probabilities, that the defendant's breach of duty was a factual cause of the damage suffered.
Limitations of the 'But For' Test
The 'but for' test works well in simple cases with a single, clear cause. However, it becomes problematic where multiple factors, potentially involving different parties or sources, might have contributed to the claimant's harm.
Consider a scenario where a claimant is exposed to harmful dust from two sources: one resulting from the employer's negligence ('guilty dust') and another naturally present ('innocent dust'). If the resulting lung disease is cumulative (caused by the build-up of dust over time), it may be impossible to prove that but for the guilty dust, the claimant would not have contracted the disease. The disease might have developed anyway from the innocent dust. In such cases, applying the 'but for' test strictly could lead to an unjust outcome, absolving a negligent defendant whose actions clearly played a role in the harm.
Multiple Causes: The Material Contribution Exception
To address the limitations of the 'but for' test in situations involving multiple potential causes, the courts developed the 'material contribution' principle. This allows causation to be established if the claimant can prove that the defendant's breach made a 'material' (i.e., more than negligible) contribution to the harm suffered.
Material Contribution to Harm
This test applies primarily where the harm is 'cumulative' – meaning its severity increases with the level of exposure to the harmful agent, and multiple sources contribute to that exposure.
Key Term: Material Contribution to Harm An exception to the 'but for' test where the defendant's breach can be proven to have made a contribution of real significance to the claimant's injury, typically used in cases involving cumulative causes.
The leading case is Bonnington Castings Ltd v Wardlaw [1956] AC 613.
Worked Example 1.1
A factory worker develops lung disease (pneumoconiosis) after years of inhaling dust. Some dust comes from a faulty machine due to the employer's negligence ('guilty dust'), while other dust is natural to the process and not due to negligence ('innocent dust'). Medical evidence indicates the disease is cumulative, caused by the total dust inhaled, but cannot isolate the effect of the 'guilty' dust alone. Can factual causation be established against the employer?
Answer: Yes, likely. Applying the Bonnington Castings principle, the claimant does not need to prove that but for the 'guilty dust' they would not have contracted the disease. They only need to show that the 'guilty dust' resulting from the employer's breach made a material contribution to the overall dose of dust inhaled, and thus to the development or severity of the disease.
Material Increase in Risk
A further refinement applies in cases of scientific uncertainty, where it's impossible to prove even a material contribution to the harm itself, often because the disease could be triggered by a single exposure, and there were multiple potential sources of exposure. In such cases, the courts may find causation established if the defendant's breach materially increased the risk of the claimant suffering the harm.
Key Term: Material Increase in Risk An exception to the 'but for' test, used in cases of scientific uncertainty, where the defendant's breach significantly increased the probability of the claimant suffering the type of injury they did, even if direct contribution to the injury cannot be proven.
The key case here is McGhee v National Coal Board [1973] 1 WLR 1. Mr McGhee developed dermatitis after working in brick kilns. His employer negligently failed to provide washing facilities, meaning he cycled home covered in abrasive brick dust. Medical evidence couldn't prove the dermatitis was caused by the extended exposure due to lack of washing facilities, as opposed to the exposure during work itself. However, the House of Lords held the employer liable because the failure to provide showers materially increased the risk of dermatitis developing.
This principle was famously applied in mesothelioma cases, such as Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22. Mesothelioma can be caused by a single asbestos fibre, and claimants often worked for multiple employers, each negligently exposing them to asbestos. It was scientifically impossible to determine which employer's asbestos fibre caused the cancer. The House of Lords held that each employer who had materially increased the risk of the claimant contracting the disease was liable.
Exam Warning
Do not confuse 'material contribution to harm' (Bonnington) with 'material increase in risk' (McGhee/Fairchild). The former applies to cumulative conditions where the defendant's breach adds to the overall 'dose' causing harm. The latter applies where science cannot determine which of several exposures caused the harm (often single-trigger conditions), but the defendant's breach significantly increased the chance of it occurring. The Fairchild application is particularly relevant for mesothelioma claims.
Scope of the Material Increase in Risk Test
The courts have been cautious about extending the McGhee/Fairchild principle beyond cases involving scientific uncertainty like mesothelioma. In Wilsher v Essex Area Health Authority [1988] AC 1074, a premature baby suffered blindness. There were five potential causes, only one of which was negligent (excess oxygen administered by the hospital). The House of Lords refused to apply the 'material increase in risk' test, distinguishing it from McGhee. In Wilsher, there were multiple distinct potential causes, whereas in McGhee, there was only one agent (brick dust) causing the harm, with the negligence relating to the duration of exposure increasing the risk from that single agent. The claimant in Wilsher failed because they couldn't prove, on the balance of probabilities, that the hospital's negligence, rather than one of the other four non-negligent factors, caused the blindness.
Multiple Causes: Consecutive Events
Difficulties also arise when a claimant suffers harm from an initial tortious event, and then a subsequent, unrelated event occurs which impacts the same interest or causes similar harm.
Worked Example 1.2
Driver A negligently injures Claimant's leg, causing permanent disability and loss of earnings. Three years later, before the negligence claim is settled, Claimant is diagnosed with an unrelated spinal disease which would also have rendered them unable to work from that point onwards. Is Driver A liable for the Claimant's loss of earnings after the onset of the spinal disease?
Answer: No. Following Jobling v Associated Dairies Ltd [1982] AC 794, the onset of the unrelated illness is considered a supervening event (a 'vicissitude of life') that breaks the chain of causation for future loss of earnings attributable to the initial accident. Driver A's liability for lost earnings ceases at the point the disease would have prevented the Claimant from working anyway.
This contrasts with Baker v Willoughby [1970] AC 467, where the claimant's leg, already injured by the defendant's negligence, was later amputated after being shot by robbers. The House of Lords held the first defendant remained liable for the ongoing effects of the initial injury, including lost earnings, even after the amputation. The reasoning was that the second event (the shooting) was also a tort, and the second tortfeasor should only be liable for the additional damage caused. The shooting did not eliminate the disability caused by the first tort. The courts distinguish Baker (two torts) from Jobling (tort followed by natural illness).
Multiple Tortfeasors and Indivisible Injuries
Where multiple defendants simultaneously or consecutively contribute to a single indivisible injury (an injury whose damage cannot be practically broken down and attributed to specific causes), the 'material contribution to harm' test applies.
Worked Example 1.3
A pedestrian is struck first by negligent driver A, then immediately afterwards by negligent driver B. The pedestrian suffers multiple severe injuries, but it's impossible to determine which specific injury was caused by which impact. Are both drivers liable?
Answer: Yes. As established in Fitzgerald v Lane [1989] AC 328, where two or more defendants breach their duty and contribute to a single indivisible injury, both can be held fully liable (jointly and severally) for the claimant's loss, subject to apportionment between themselves under the Civil Liability (Contribution) Act 1978. Factual causation is established against each driver because their negligence materially contributed to the overall injuries.
Revision Tip
When faced with multiple causes, first identify the type of injury. Is it cumulative (Bonnington applies - material contribution to harm)? Is it a single-trigger condition with scientific uncertainty about the source (Fairchild applies - material increase in risk)? Or is it an indivisible injury caused by concurrent or consecutive torts (Fitzgerald applies - material contribution to harm)? This dictates the correct causation test.
Key Point Checklist
This article has covered the following key knowledge points:
- Factual causation in negligence typically requires the claimant to satisfy the 'but for' test.
- The 'but for' test is inadequate where multiple factors may have caused the claimant's harm.
- Where harm is cumulative and multiple sources contribute, the 'material contribution to harm' test applies (Bonnington Castings).
- Where harm could be caused by a single exposure but there are multiple potential sources and scientific uncertainty, the 'material increase in risk' test may apply (McGhee, Fairchild).
- The 'material increase in risk' test is generally confined to cases of scientific uncertainty, like mesothelioma, and was distinguished in cases with multiple distinct potential causes (Wilsher).
- For consecutive causes, a subsequent non-tortious event may break the chain of causation (Jobling), but a subsequent tortious event may not fully extinguish the first tortfeasor's liability (Baker).
- Where multiple tortfeasors contribute to a single indivisible injury, each can be liable for materially contributing to the harm (Fitzgerald).
Key Terms and Concepts
- Factual Causation
- Material Contribution to Harm
- Material Increase in Risk
