Negligence: Causation, Remoteness and the Wagon Mound Principle
This domain separates two questions examiners love to conflate: did the defendant's breach actually cause the damage (causation in fact), and if so, is that damage close enough in law (remoteness)?
Causation in fact
- But-for test: would the damage have occurred anyway? Barnett v Chelsea and Kensington HMC - the doctor's failure did not cause the death, because the poisoning would have killed the patient regardless.
- Multiple causes: where the but-for test is unworkable, a material contribution suffices (Bonnington Castings v Wardlaw). In industrial disease and similar cases, a material increase in risk may be enough (Fairchild v Glenhaven).
- Unknown causes: where the harm could arise from several sources, the claimant must show which (Wilsher v Essex AHA).
- Novus actus interveniens: a reasonable act in the defence of life or property, or an independent third-party act, can break the chain; negligent medical treatment usually does not.
Remoteness: Wagon Mound (No 1)
Overseas Tankship (UK) Ltd v Morts Dock (The Wagon Mound No 1) displaced Re Polemis: the defendant is liable only for damage of a kind that a reasonable person would foresee, not for every direct consequence. The precise manner or extent need not be foreseen (Hughes v Lord Advocate; Jolley v Sutton).
The thin skull rule
The defendant takes the claimant as he finds him: an unforeseeable severity of a foreseeable kind of injury is no answer (Smith v Leech Brain). The rule applies to the extent of damage, not to create liability for an unforeseeable type of damage.
Worked example
A driver negligently leaves a van across a road. A second driver swerves, hits a lamp-post, and the lamp falls on a bystander already suffering from brittle bones, whose leg fractures. Causation: but for the van blocking the road, the collision would not have occurred. Remoteness: collision and injury are foreseeable kinds of harm; the lamp falling is not so unusual a mechanism as to be unforeseeable. The brittle bones affect only quantum under the thin skull rule.
Traps that cost marks
Answering remoteness with the direct-consequence test still; treating thin skull as covering unforeseeable kinds of damage; confusing material contribution to injury with material contribution to risk; and forgetting that intervening negligent medical treatment usually does not sever the chain.