To right a private wrong, causation is generally established between the tortfeasor’s negligent act and claimant’s injury. However, on occasion, the evidence will be such that a causal link is difficult or even impossible to prove by the traditional approach. Material contribution has emerged in tort law to attempt to impose liability where causation is hard to prove in the usual manner, or where applying traditional causation would lead to an undesirable outcome. It is needed to protect vulnerable claimants who should not be barred from seeking remedy merely because their particular circumstances make it harder for them to obtain damages. A comparison of traditional factual causation with material contribution shows how the underlying principles of protecting the claimant are compatible without direct causation. Despite not being a traditional test of causation, material contribution in the law of tort is still needed to solve the problem of an evidentiary gap when the but-for test is insufficient to impose liability where it is desirable. Moreover, it may still be possible to show some level of causal link between the defendant’s negligence and the claimant’s injury.
The but-for test is the traditional method of proving factual causation in tort law, such as that applied in Barnett v Chelsea and Kensington Hospital Committee.1 It aims to show the connection between the defendant’s breach and the claimant’s loss in order to justify the defendant being held liable for that loss. The test requires a burden of proof on a balance of probabilities2 and disregards conditions which are ‘part of the normal environment’.3 It tends to take into account the phenomena of multiple causes and divisible injuries, and arguably aims to hold tortfeasors accountable for the damage that they have caused by their negligence to the claimant. In Barnett, Neild J found that the defendant’s negligence did not cause the victim’s death; but for the defendant’s breach of the duty of care, the same outcome of the victim’s death by arsenic poisoning would have occurred.4
In Bonnington Castings Ltd v Wardlaw, Lord Reid stated that ‘what is a material contribution must be a question of degree’.5 He observed that if a factor was too important an issue to fall under the de minimis non curat lex exception, then it could not be too small to be considered immaterial. Jane Stapleton has pointed out that there remains some ambiguity which can be outlined in three scenarios, two of which follow orthodox causation and one of which is more difficult to resolve.6 This will be explored in the context of multiple tortfeasors, such as where the victim was in the employ of multiple firms over his career and exposed to dangerous materials.
In the first situation, total injury is divisible: it is possible to determine who caused which part of the claimant’s injury and apportion damages accordingly. Divisible injuries take into account how severe the injury is and whether and how each tortfeasor’s actions exacerbated the harm. In addition, the alternative approach of the quantification of damages considers ‘the fact that absent the breach this precise total condition would not have been suffered’.7 However, quantification is not necessarily the best approach to take because of the complex problems it poses in terms of proof: ‘where the disease manifests itself many years after the exposure … much of the detail is inevitably lost’.8 The second type of case involves indivisible total injury, where each defendant is found jointly and severally liable for the entire injury. In both of these cases, there is a causal link between each defendant’s act and the claimant’s injury; imposing liability upon the defendants for the harm they are shown to be responsible for should not be controversial.
The third situation is more controversial because it has features from each of the first two scenarios that usually arise. Unlike in Bonnington, this principle concerns material contribution to the risk of injury as opposed to material contribution to injury itself. On one hand, each tortfeasor’s act contributes to an accumulation of risk of the claimant contracting the disease. On the other hand, the injury is indivisible because once manifested, the disease’s effects are the same regardless of the victim’s history of exposure. It is also unclear at which point along the line of exposure the victim actually contracted the disease, so it is harder to find one defendant directly responsible for the disease itself. These conditions are relevant in cases where the claimant suffers or even dies from mesothelioma, for example, a medical condition caused by the inhalation of asbestos to which certain employers may negligently expose their employees. Difficulty in finding liability is problematic because the role of the court in tort law should be to allow private wrongs to be compensated without being fettered by scientific impossibilities or evidentiary gaps. Therefore, concepts such as material contribution to risk of injury and material contribution to injury have been developed and should be retained to combat the tension.
Authorities have equated the material contribution to risk of injury with causation. For example, in Fairchild v Glenhaven Funeral Services Ltd, material contribution to the risk of injury was a sufficient causal connection and was equivalent to a material contribution to the disease despite the ‘inability to prove what is scientifically unprovable’.9 The Fairchild principle clashes with the but-for test: the claimant was unable to show which defendant caused the harm on a balance of probabilities; it was necessary to create an exception without involving but-for causation. On balance, accepting that there was a causal link despite the evidentiary gap would have led to a fairer outcome than failing to compensate the claimant for an injury that was definitely caused by a wrongdoer. Although the court’s preference for policies to protect claimants and warn employers is understandable, it seemed to remain unclear that there was direct causality. This could imply that the legal test has become easier to satisfy when the traditional test cannot be applied. However, it would be counterintuitive to argue that there was no causal link between the tortfeasors’ actions and the claimant’s injury at all, because in that case the claimant’s disease would have - impossibly - been caused by nothing! In cases such as this, not only is material contribution necessary to impose liability on irresponsible tortfeasors, but it is a test that results in a net positive. Penalising employers for increasing the risk of an injury is justified when in fact that injury materialises, even if that must be squared with liability for increasing the risk of an injury without an actual resulting harm being less reasonable.
Similarly, material contribution to injury has also been understood to equal causing the injury, as was decided in Williams v Bermuda Hospitals Board.10 Since the patient was already suffering from sepsis before the hospital’s negligence, it was unclear that the breach of duty made the injury itself worse. This would have rendered the but-for test useless to the claimant: but for the hospital’s negligence, the patient could still have suffered the same injuries from sepsis. A strict application of the but-for test would bar the claimant from seeking damages. However, the hospital’s negligence did lead to the build up of more sepsis which materially contributed to the state of affairs, potentially causing more injury to the patient’s heart and lungs. By extending the principle of causation to include material contribution, the court was able to allow redress.
In some cases of over-determination, applying the but-for test could create the false negative reasoning that but for one’s conduct, the claimant still could have died from the other’s conduct, leading to neither defendant being held liable. Richard Wright’s NESS (necessary element of a sufficient set) test aims to determine whether the defendant’s conduct was significant enough to attract liability in a ‘sufficient set’ of factors.11 This test attempts to establish a historical connection between the tortious conduct and its outcome; thus, it has many similarities to causation. Jane Stapleton has suggested a more accessible ‘targeted but-for test’, which removes complicating factors to satisfy the but-for test. For example, by removing one defendant from the equation, the other defendant would be able to satisfy the but-for test.12 This explains how each factor can be historically involved in an outcome even though the other factor could have been responsible. Thus, an element of causation is retained.
Perhaps the difference between material contribution and the but-for test should be reconciled by establishing material contribution as an alternative test or, as Stephen Bailey suggests, a particular application of but-for causation in cases of cumulatively-caused injury.13 If material contribution were an alternative test of causation, it would ask the question of factual causation through a normative lens, so that a court could still impose liability where an evidentiary gap makes it difficult to apply the but-for test.
Alternatively, it could be argued that material contribution is not another test for causation. Rather, it is the exceptional imposition of liability in the absence of causation. In mesothelioma cases, because the symptoms may take years to materialise, although the cancer is linked to asbestos exposure, the ability to prove that a defendant’s negligence caused the claimant’s injury is severely compromised. This was exposed in Barker v Corus UK Ltd, where an ‘innocent’ potential cause for the claimant’s mesothelioma was present.14 In Fairchild, it seemed to be certain that at least one defendant would be responsible. Of course, it should be noted that Stapleton holds the view that the ‘defendant could always in theory point to environmental exposures’.15 In Barker, there was truly a chance that none of the defendants were responsible. Therefore, the court’s aim might not have been to hold the defendants liable for the damage caused; their decision seemed to place emphasis on warning employers against a breach of duty. This policy approach, which considerably disregards causation as the deciding factor in favour of warning other employers against irresponsible behaviour, could be undesirable and even raise fair labelling issues: even in the face of an innocent cause, the law considers the defendants as if they were directly responsible for the claimant’s injury. Although it could be argued that such a policy approach still relies on a causal link to attach responsibility to employers who place their workers in dangerous working conditions, in cases such as Barker, the claimant does not seem to have to fulfil the normal standard of proof at all.
Imposing liability without a proven causal link would establish material contribution as an court-created exception outside the scope of causation. In light of new legislation which imposes the whole of the damage upon all defendants, this development in tort law may go too far.16 Draconian consequences are created in cases where even a small increase to the risk of mesothelioma may result in the defendant having to pay full damages.17
Material contribution must have a place in the law today as it promotes the policy of compensating those who have suffered grave harm. Logistical problems arising from imposing liability cannot outweigh the injustice of denying victims redress. As a means for the courts to impose liability, material contribution does not mean that causation cannot be proved. In situations such as mesothelioma claims, the courts are merely required to expand their understanding of causation beyond the traditional but-for approach in order to accommodate for evidentiary gaps.
  1 QB 428,  2 WLR 422.
 Wilsher v Essex AHA  AC 1074,  2 WLR 557.
 Reeves v Commissioner of Police for the Metropolis  1 AC 360 at 391, per Lord Hobhouse.
 Barnett (n 1).
  AC 613,  2 WLR 707.
 J Stapleton, ‘Cause-in-Fact and the Scope of Liability for Consequences’ (2003) 119 LQR 389.
 J Stapleton, ‘Unnecessary Causes’ (2013) 129 LQR 39.
 Holtby v Brigham  3 All ER 421.
  UKHL 22,  1 AC 32 .
  UKPC 4,  AC 888.
 R Wright, ‘Once More into the Bramble Bush: Duty, Causal Contribution, and the Extent of Legal Responsibility’ (2001) 53 Vanderbilt LR 1071, pp 1102-1103.
 Stapleton (n 5).
 Bailey, ‘Causation in negligence: what is a material contribution?’ (2010) 30 LS 167.
  UKHL 20,  2 AC 572.
 J Stapleton, ‘Lords A-Leaping Evidentiary Gaps’ (2002) 10 Tort LJ 276.
 Compensation Act 2006, s 3.
 Sienkiewicz v Greif (UK) Ltd  UKSC 10,  2 AC 229.