Causation in Tort Law
Introduction
Causation is a fundamental element of liability in tort law. Before a defendant can be held liable in negligence (and in many other torts), the plaintiff must show that the defendant's conduct actually caused the harm complained of, and that the harm is not too remote a consequence of that conduct. Indian tort law is largely uncodified and draws heavily on English common law principles, so the leading tests on causation come from decided cases rather than from statute.
This guide explains the two questions courts ask on causation, the tests used to answer each, and how intervening events and multiple causes are handled.
The Two Questions of Causation
Causation is analysed in two stages:
- Factual causation (causation in fact) — Did the defendant's act or omission, as a matter of fact, bring about the harm?
- Legal causation (causation in law / remoteness) — Even if the defendant caused the harm in fact, is the harm sufficiently connected to the wrongful conduct that the law should impose liability, or is it too remote?
A plaintiff must succeed on both. Establishing factual causation alone is not enough; the harm must also pass the test of legal causation.
Factual Causation: The "But-For" Test
The standard test for factual causation is the but-for test: would the harm have occurred but for the defendant's wrongful conduct? If the harm would have happened anyway, the defendant's conduct is not a factual cause.
Illustrative case — Barnett v Chelsea and Kensington Hospital Management Committee [1969] 1 QB 428. A night-watchman who had drunk poisoned tea attended a hospital, but the doctor negligently failed to examine him and sent him away; he later died of arsenic poisoning. The court held that although the doctor was negligent, the negligence was not the cause of death, because the evidence showed the man would have died of the poisoning even if he had been treated. The but-for test was not satisfied, so the claim failed.
The case shows that a breach of duty does not create liability unless it is causally connected to the harm.
Limits of the But-For Test
The but-for test does not work well where two or more sufficient causes operate together, or where medical/scientific evidence cannot pinpoint a single cause. In such situations courts have used a "material contribution to the harm" or "material increase in risk" approach, holding a defendant liable where the wrongful conduct materially contributed to, or materially increased the risk of, the injury even though it cannot be shown to be the sole but-for cause.
Legal Causation and Remoteness of Damage
Once factual causation is established, the court asks whether the damage is too remote. The governing test is reasonable foreseeability: the defendant is liable only for the kind of harm that a reasonable person could have foreseen as a consequence of the wrongful conduct.
Illustrative case — Overseas Tankship (UK) Ltd v Morts Dock & Engineering Co (The Wagon Mound, No. 1) [1961] AC 388. Oil negligently discharged into a harbour spread to a wharf and later ignited, damaging the wharf. The Privy Council held that the defendants were not liable for the fire damage because fire was not a reasonably foreseeable consequence of spilling the oil. This case replaced the older "directness" test (from Re Polemis) with the modern foreseeability test for remoteness.
The Thin-Skull (Egg-Shell Skull) Rule
An important qualification to foreseeability is the thin-skull rule: a defendant must take the victim as he finds them. If some injury of a foreseeable kind is caused, the defendant is liable for the full extent of that injury even if it is unexpectedly severe because of the victim's pre-existing vulnerability.
Illustrative case — Smith v Leech Brain & Co Ltd [1962] 2 QB 405. Due to the employer's negligence, a workman was burned on the lip by molten metal. The burn triggered a cancer in pre-malignant tissue, and he died. The court held the employer liable for the death: since a burn (some injury) was foreseeable, the defendant was liable for its full consequences even though the fatal cancer was not itself foreseeable. This is the classic authority for the thin-skull principle, not a "faulty ladder" case.
Intervening Acts (Novus Actus Interveniens)
The chain of causation between the defendant's wrongful act and the harm may be broken by a new intervening act (novus actus interveniens) — an independent event, a third party's act, or the plaintiff's own conduct — that is sufficiently unforeseeable or unrelated. If the chain is broken, the defendant is not liable for the harm that follows the intervening act.
Foreseeable intervening events generally do not break the chain; only an unforeseeable, independent act that becomes the effective cause of the harm does so.
Illustrative case — Palsgraf v Long Island Railroad Co., 248 NY 339 (1928). A landmark American decision (per Cardozo J) closely tied to causation and foreseeability. Railroad staff, helping a passenger board a moving train, dislodged a package of fireworks that exploded; the blast was said to have toppled scales at the far end of the platform, injuring Mrs Palsgraf. The court held the railroad not liable because the injury to her was not a reasonably foreseeable consequence of the staff's conduct — there was no duty owed to an unforeseeable plaintiff. The case is a cornerstone of the foreseeability approach to proximate cause.
Multiple Causes and Multiple Defendants
Where several causes combine to produce a single injury, or several parties contribute to it, courts may:
- Apportion liability between defendants according to their respective share of responsibility; and/or
- Hold defendants jointly and severally liable, so the plaintiff may recover the whole loss from any one of them, leaving that defendant to seek contribution from the others.
The material-contribution approach mentioned above is often applied in these situations, particularly where the precise contribution of each cause cannot be scientifically separated (for example, cumulative exposure to a harmful substance from multiple sources).
Summary
| Question | Test | Leading authority |
|---|---|---|
| Factual causation | But-for test (and material contribution where but-for fails) | Barnett v Chelsea & Kensington |
| Legal causation / remoteness | Reasonable foreseeability of the kind of harm | The Wagon Mound (No. 1) |
| Extent of harm | Thin-skull rule: take the victim as you find them | Smith v Leech Brain |
| Breaking the chain | Novus actus interveniens (unforeseeable independent act) | Palsgraf (foreseeability of harm/plaintiff) |
Conclusion
To establish liability, a plaintiff must show both that the defendant's conduct was a factual cause of the harm (usually through the but-for test) and that the harm was a foreseeable, non-remote consequence of that conduct. The thin-skull rule extends liability to the full extent of a foreseeable kind of injury, while an unforeseeable intervening act may cut off liability. Because Indian tort law follows the common law, students should study these leading English and American authorities closely and note how Indian courts have adopted and applied the same reasoning.
Glossary
- Factual causation: Whether the defendant's conduct actually brought about the harm, tested primarily by the but-for test.
- But-for causation: The harm would not have occurred but for the defendant's wrongful conduct.
- Legal causation / remoteness: Whether the harm is sufficiently connected to the wrongful conduct to justify liability, tested by reasonable foreseeability.
- Thin-skull (egg-shell skull) rule: A defendant is liable for the full extent of a foreseeable kind of injury even if it is unexpectedly severe due to the victim's vulnerability.
- Novus actus interveniens: A new intervening act that breaks the chain of causation and relieves the defendant of liability for later harm.
- Joint and several liability: Where each of several defendants can be held liable for the whole of the plaintiff's loss.