← The hardest concepts in United States law
In one breath
Proximate cause, also called scope of liability, limits a defendant’s responsibility to harms that fall within the risks that made the conduct careless in the first place. A defendant whose carelessness was a but-for cause of an injury is still not liable if the harm is too remote or of a kind the carelessness did not make likely.
The picture
The guardrail on the mountain road
A guardrail goes up on a mountain road because cars might go over the edge. If the builder leaves it out, the builder answers for the cars that go over. But suppose a rockfall crushes a car on the same bend. The missing rail had nothing to do with that. The rail was needed for the danger it guards against, and responsibility for its absence follows that danger and no other.
That is the structure of proximate cause. First, would the harm have happened without the careless act? That is the road itself: no road, no accident. Then comes the guardrail question: was this harm the kind of harm, arising through the kind of sequence, that made the act careless? If so, the builder answers. If the harm is a freak that the rail was never meant to cover, the chain stops, however direct the physical link.
Where the picture stops working
A guardrail’s purpose is plain to see, while in law the scope of the risk is a judgment that courts describe in different words: foreseeability, direct consequences, the zone of danger. The picture also does not show intervening events, such as another driver’s wildly reckless act, which can cut the chain, or the thin-skull rule, under which a defendant takes the victim as found.
How it really works
- 1Establish actual cause: but for the defendant’s conduct, the harm would not have occurred (or the conduct was a substantial factor where several causes each would have sufficed).
- 2Identify the risks that made the conduct careless: the reasons a reasonable person would have avoided it.
- 3Compare the harm with those risks. Is the type of harm, and the general way it came about, among them? The exact details need not have been foreseeable.
- 4Look for intervening or superseding causes. Foreseeable events, such as a rescue attempt or ordinary medical negligence in treating the injury, usually do not cut the chain. Extraordinary or unforeseeable ones may.
- 5Apply the thin-skull rule. Once the type of harm is within the risk, the defendant is liable for its full extent even if the plaintiff was unusually vulnerable.
Why people get it wrong
- Running together but-for causation and proximate cause. The first is factual and the second is a limit based on the scope of the risk; both are required.
- Using hindsight. The question is whether the risk made the conduct careless, not whether the harm could have been predicted with certainty after the event.
- Assuming any intervening act breaks the chain. Many do not, if they are within the risk the defendant created.
- Demanding that the precise sequence of events be foreseeable. The general type of harm and the general manner of its occurrence are enough.
- Forgetting the thin-skull rule, which separates the type of harm (which must be within the risk) from its extent (which need not be).
A worked example
The facts are invented
Rocco carelessly leaves a ladder across a sidewalk in the invented town of Calder. A pedestrian trips on it and breaks her arm. That is the harm that made leaving a ladder there careless, and Rocco is liable. If she has unusually brittle bones and the arm shatters far worse than a normal arm would, Rocco is liable for the whole of the injury, because the type of harm was within the risk.
At the hospital a doctor treats the arm with ordinary negligence, and it heals badly. Rocco generally remains liable for the worsened result too, since medical treatment of the injury is a foreseeable consequence of causing it. Change the facts again. A thief picks up the ladder, uses it to climb into a neighbor’s window and steals a necklace. Rocco’s carelessness was a but-for cause of the burglary, since the ladder was there. But the risk that made leaving it careless was tripping, not theft, so the burglary is outside the scope of his liability.
Try it
A railroad guard carelessly pushes a passenger who is boarding a moving train. The passenger drops a package that looks harmless but holds fireworks. The explosion topples scales on a distant platform and injures a waiting woman. On the reasoning of the New York court in the famous case on these facts, what is the result?
Landmark authorities
Read the sources themselves; this list is a starting point.
- Palsgraf v. Long Island Railroad Co., 248 N.Y. 339, 162 N.E. 99 (1928)
- Overseas Tankship (U.K.) Ltd. v. Morts Dock & Engineering Co. (The Wagon Mound No. 1), [1961] A.C. 388 (Privy Council)
- Restatement (Third) of Torts: Liability for Physical and Emotional Harm, section 29 (2010)
Where to go next
More hard concepts in United States law
- Easements and covenants running with the land (Property law)
- The battle of the forms (UCC 2-207) (Contracts)
This page is an educational overview. It is not legal advice and not a substitute for the sources: the statute, the rule, the case itself. United States law is made in fifty states and in the federal system, and the rules differ between them. Each page states the usual formulation of the rule and names landmark decisions; your own state, circuit or course may use different wording. Check the primary sources before relying on any rule.