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Even if the claimant proves that the defendant owed a duty of care and breached it, the claim will fail unless the claimant can also prove that the breach caused the damage and that the damage was not too remote. Causation is often the most complex and contested element of a negligence claim. This lesson examines factual causation (the "but-for" test), legal causation (remoteness of damage), the thin skull rule, the doctrine of novus actus interveniens, and problems arising from multiple causes.
Causation in negligence involves two distinct questions:
Both elements must be satisfied for the claimant to succeed.
flowchart TD
A["Did D's breach<br/>cause C's damage?"] --> B{"1. FACTUAL CAUSATION<br/>But-for test"}
B -- "But for the breach,<br/>damage would still<br/>have occurred" --> Z["Causation FAILS<br/>— claim fails"]
B -- "But for the breach,<br/>damage would NOT<br/>have occurred" --> C{"2. LEGAL CAUSATION<br/>Remoteness test"}
C -- "Type of damage<br/>NOT reasonably<br/>foreseeable" --> Z
C -- "Type of damage<br/>WAS reasonably<br/>foreseeable" --> D["Causation<br/>ESTABLISHED"]
style A fill:#1a5276,color:#fff
style D fill:#27ae60,color:#fff
style Z fill:#c0392b,color:#fff
The but-for test asks: but for the defendant's breach of duty, would the claimant have suffered the damage?
If the answer is "yes — the claimant would have suffered the damage anyway" — then the defendant's breach did not cause the damage, and the claim fails on causation.
If the answer is "no — the claimant would not have suffered the damage but for the defendant's breach" — then factual causation is established.
| Aspect | Detail |
|---|---|
| Facts | Three night watchmen attended the casualty department complaining of vomiting after drinking tea. The doctor on duty refused to see them and told them to go home and see their own doctors. One of the men, Mr Barnett, died later that night from arsenic poisoning. |
| Decision | The hospital was in breach of duty (the doctor should have examined the patients). However, the claim failed on causation. Even if the doctor had examined Mr Barnett, it was too late to save him — the arsenic poisoning was too far advanced. He would have died regardless of the doctor's breach. |
| Principle | The but-for test: the breach must be the actual cause of the damage. If the damage would have occurred anyway, factual causation is not established. |
A boy fell from a tree and injured his hip. The hospital negligently failed to diagnose the injury for five days. The claimant argued that the delay caused avascular necrosis (death of the bone tissue) in his hip. The evidence showed that even with prompt treatment, there was a 75% chance the condition would have developed anyway. The House of Lords held that factual causation was not established — on the balance of probabilities, the damage would have occurred regardless.
The but-for test works well in straightforward cases, but it can produce difficulties in certain situations.
Where there are multiple potential causes of the claimant's damage, the but-for test may fail to identify the actual cause, leading to injustice.
Fairchild v Glenhaven Funeral Services Ltd [2002]
| Aspect | Detail |
|---|---|
| Facts | Mr Fairchild developed mesothelioma (a cancer caused by exposure to asbestos) after working for several different employers, all of whom had negligently exposed him to asbestos. Medical science could not determine which employer's asbestos had caused the disease. |
| The problem | Using the strict but-for test, Mr Fairchild could not prove that "but for" the breach of any individual employer, he would not have developed the disease — because any one of the other employers might have been the actual cause. |
| Decision | The House of Lords departed from the strict but-for test. It held that where: (1) the claimant was exposed to asbestos by multiple employers; (2) all were in breach of duty; and (3) the claimant could not prove which employer's breach actually caused the disease — it was sufficient to show that each employer had materially increased the risk of the claimant developing the disease. |
| Principle | The "material increase in risk" test may replace the but-for test where the strict test produces manifest injustice. |
This principle was further developed in Barker v Corus UK Ltd [2006] and subsequently modified by the Compensation Act 2006, s3, which provides that in mesothelioma cases, each employer is jointly and severally liable for the full extent of the damage.
The courts have generally been reluctant to allow claims based on the loss of a chance in clinical negligence cases.
Gregg v Scott [2005] — A doctor negligently misdiagnosed a lump as benign. The delay in treatment reduced the claimant's chances of survival from 42% to 25%. The House of Lords held (by 3–2) that the claim failed — the claimant could not show, on the balance of probabilities, that he would have been cured "but for" the negligence.
Even if factual causation is established, the claimant must also prove that the damage was not too remote. This is a question of legal causation — not all damage that flows from a breach is recoverable; the law draws a line beyond which the consequences are considered too distant or unforeseeable.
| Aspect | Detail |
|---|---|
| Facts | Oil was carelessly spilled from a ship (the Wagon Mound) in Sydney Harbour. The oil spread across the water to a wharf where welding work was being carried out. Sparks from the welding ignited the oil, causing a fire that damaged the wharf. |
| Decision | The Privy Council held that the defendant was not liable for the fire damage. Although the oil spill was negligent and caused some direct damage (pollution of the wharf), the fire damage was too remote. It was not reasonably foreseeable that furnace oil spread on water would ignite. |
| The test | The remoteness test is based on reasonable foreseeability of the type of damage: the defendant is liable only for damage of a type that was reasonably foreseeable at the time of the breach. |
This replaced the earlier "direct consequence" test from Re Polemis [1921], which had held the defendant liable for all direct consequences of the breach, whether foreseeable or not.
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