Introduction
In the law of tort, a claimant must prove that the defendant’s breach of duty caused the damage they have suffered. The element of causation is divided into two parts: factual causation and legal causation. Factual causation is the first hurdle a claimant must overcome. It is concerned with establishing a physical or historical connection between the defendant’s negligence and the claimant’s injury. This essay will explain the primary legal test for establishing factual causation, the ‘but for’ test, as established in case law. It will then go on to discuss the problems that can arise with the strict application of this test and examine the modified approaches the courts have developed in response to these challenges in certain types of cases.
The ‘But for’ Test and its Limitations
The starting point for determining factual causation is the ‘but for’ test. This asks the question: ‘but for the defendant’s breach of duty, would the claimant have suffered the harm?’ If the claimant would have suffered the harm anyway, regardless of the defendant’s actions, then factual causation is not established, and the claim will fail. The burden is on the claimant to prove, on the balance of probabilities, that the defendant’s breach caused the harm (Horsey and Rackley, 2021).
The classic authority for this principle is *Barnett v Chelsea & Kensington Hospital Management Committee* [1969] 1 QB 428. In this case, a man went to a hospital emergency department complaining of stomach pains and vomiting after drinking tea. The doctor on duty, in breach of his duty of care, failed to see and examine him, instead sending him home with instructions to see his own doctor. The man died a few hours later from arsenic poisoning. His widow sued the hospital. The court held that the hospital was not liable. Although the doctor had been negligent, the evidence showed that even if the man had been properly examined and admitted, he would have died anyway as the poisoning was too advanced. Therefore, ‘but for’ the doctor’s negligence, the man would still have died. Causation could not be established.
However, the ‘but for’ test can lead to unjust results in situations where there are multiple potential causes of harm. The courts have recognised that a rigid application of the test in these circumstances could leave a deserving claimant without a remedy. This has led to the development of exceptions. One such exception is the ‘material contribution to harm’ principle. In *Bonnington Castings Ltd v Wardlaw* [1956] AC 613, the claimant contracted a lung disease from inhaling silica dust at work. Some of the dust came from a source for which the employer was not negligent (the ‘innocent’ dust), and some came from a source for which the employer was negligent (the ‘guilty’ dust). It was impossible to prove that ‘but for’ the guilty dust, the claimant would not have contracted the disease. The House of Lords held that the claimant did not need to prove this. Instead, it was sufficient to show that the defendant’s breach had made a ‘material contribution’ to the disease. As the guilty dust was found to be a material cause, the defendant was held liable.
This approach was extended further in cases involving a ‘material increase in risk’. In *McGhee v National Coal Board* [1973] 1 WLR 1, a worker contracted dermatitis. The possible cause was exposure to brick dust during the working day, for which the employer was not liable. However, the employer was in breach of duty for failing to provide washing facilities, which meant the claimant had to cycle home with the dust still on his skin, prolonging the exposure. The medical evidence could not establish whether the dermatitis was caused by the initial exposure or the prolonged exposure. The House of Lords found that by failing to provide showers, the defendant had materially increased the risk of the claimant contracting the disease, and this was treated as equivalent to making a material contribution to the harm itself. This principle was later considered and applied in the specific context of multiple employers in the asbestos case of *Fairchild v Glenhaven Funeral Services Ltd* [2002] UKHL 22.
Conclusion
In conclusion, the main test for factual causation in tort is the ‘but for’ test, which asks whether the harm would have occurred but for the defendant’s negligent act. This is clearly demonstrated in the case of *Barnett*. However, this test is a blunt instrument that does not always work fairly, especially in cases where there are multiple cumulative causes of an injury. To address this, the courts have shown a degree of flexibility. In situations involving cumulative causes or scientific uncertainty, the test has been modified. The principles of ‘material contribution to harm’ seen in *Bonnington Castings* and ‘material increase in risk’ from *McGhee* allow claimants to succeed where they can prove the defendant’s breach made the harm, or the risk of it, worse, even if they cannot satisfy the strict ‘but for’ standard. These exceptions show that the courts are willing to adapt the rules of causation to achieve a just outcome.
References
- Barnett v Chelsea & Kensington Hospital Management Committee [1969] 1 QB 428.
- Bonnington Castings Ltd v Wardlaw [1956] AC 613.
- Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22.
- Horsey, K. and Rackley, E. (2021) Tort Law. 7th edn. Oxford University Press.
- McGhee v National Coal Board [1973] 1 WLR 1.
