Causation is the third element of negligence and it comes in two parts that do different work. Actual cause is a factual question: did the breach in fact produce this harm? Proximate cause is a policy question: even though the breach produced the harm, is it fair to hold the defendant responsible for a result this remote? A plaintiff must win both. Most hard exam questions are about the second.
Rule
- But for. The harm would not have happened but for the defendant's breach.
- Substantial factor. Where two forces would each have been enough on their own, the test becomes whether the defendant's conduct was a substantial factor in producing the harm.
- Shifting the burden. Where two defendants were both negligent and only one caused the harm, some courts put the burden on each of them to disprove causation.
- Proximate cause. Liability extends to harms that are a foreseeable result of the risk the defendant negligently created.
- Intervening causes. A foreseeable intervening act does not break the chain. An unforeseeable and independent one, often called a superseding cause, does.
- The eggshell plaintiff. The extent of the harm need not be foreseeable, only its general kind, so a defendant takes the victim as found.
Leading cases
- Summers v. Tice: two hunters both fired negligently and only one hit the plaintiff, so the burden shifted to each of them to show he was not the cause.
- Overseas Tankship (UK) Ltd v. Morts Dock and Engineering Co., known as the Wagon Mound: liability turns on whether the kind of damage was reasonably foreseeable, not on how direct the sequence was.
- Palsgraf v. Long Island Railroad Co.: the dissent framed proximate cause as a question of drawing a practical line, and courts still use that framing where duty is conceded.
Where students go wrong
The first mistake is running but for causation and proximate cause together in one sentence. They are separate steps with separate answers, and separating them is free points.
The second is using but for where it does not work. When two independently sufficient causes combine, but for gives the absurd answer that neither defendant caused anything. That is exactly when the substantial factor test appears.
The third is treating foreseeability as one question. Ask whether the type of harm was foreseeable, not whether the precise sequence was. The eggshell plaintiff rule follows directly from that distinction.
FAQ
What is the difference between actual and proximate cause?
Actual cause asks whether the breach in fact produced the harm. Proximate cause asks whether the connection is close enough that the law should impose liability.
What is a superseding cause?
An unforeseeable intervening event that breaks the causal chain and relieves the original defendant. Ordinary negligence by a rescuer or a doctor treating the injury is usually foreseeable and does not.
Does the eggshell plaintiff rule apply to proximate cause?
Yes. Once a foreseeable kind of harm is established, the defendant is liable for the full extent, even where a pre-existing condition made the injury far worse.
Related terms
Working through this in your own casebook takes longer than reading it here. Syllume starts from your syllabus and turns each assigned case into a brief you can study from.