Module 2: Negligence: Duty, Breach & Causation

Every negligence claim requires four elements: duty, breach, causation (both actual and proximate), and damages — missing any single element defeats the entire claim, no matter how strong the others are.

Example. Peter drives carelessly through a red light but, by pure luck, no collision occurs and nothing is damaged — even though duty and arguably breach are present, there’s no negligence claim at all without actual damages. Compare that to the same careless driving actually causing a collision and injury — now all four elements are potentially satisfied together.

The reasonable person standard is objective — courts ask how a hypothetical reasonably careful person would have acted under the same circumstances, not what the defendant personally believed was safe. This standard adjusts for professionals (measured against a reasonably skilled practitioner) and children (measured against a reasonable child of similar age, intelligence, and experience, with exceptions for adult activities).

Vaughan v. Menlove is the real case that made this standard objective in the first place, rejecting a much more forgiving alternative. A farmer built a hay rick near his property line in a way neighbors warned him risked fire; he insisted he had acted to the best of his own honest judgment. When the hay ignited and burned down neighboring cottages, he argued he should only be judged against his own sincere best effort, not against some external standard. The court rejected that: negligence is measured against what a reasonably prudent person would have done, not the defendant’s own good-faith but possibly foolish judgment — otherwise the standard of care would vary with each individual defendant’s own level of caution, offering no real protection to anyone.

Example. Peter, a surgeon, is sued for a surgical complication — he’s measured against what a reasonably skilled surgeon would have done, not an ordinary layperson’s understanding of medicine. Now compare: a 10-year-old riding a bicycle carelessly is measured against a reasonable 10-year-old’s judgment, not an adult cyclist’s — unless that same 10-year-old is instead driving a car, an inherently adult activity, where the full adult standard would apply.

The traditional premises liability categories: invitees (there for the possessor’s business benefit, like customers) get the strongest duty, including reasonable inspection for hazards; licensees (social guests) get a duty to warn of known dangers; trespassers traditionally get minimal protection, with exceptions like the attractive nuisance doctrine for child trespassers.

Sioux City & Pacific Railroad Co. v. Stout is the real, original “turntable case” that created the attractive nuisance doctrine. A railroad left an unlocked, unguarded railway turntable near a town, where children were known to play on it; a six-year-old boy, trespassing, was seriously injured using it. The railroad argued it owed a trespasser no duty at all. The Supreme Court disagreed: where a landowner maintains a dangerous condition that’s genuinely likely to attract children too young to appreciate the danger, and the cost of guarding against it is modest relative to the risk, ordinary trespasser immunity doesn’t apply — the landowner owes real care specifically because children can’t be expected to understand what an adult trespasser reasonably should.

Example. Peter’s grocery store owes John, a shopping customer (invitee), a duty to reasonably inspect for and address hazards like spills. Now compare: Peter invites Sam over to his house purely as a social guest (licensee) — Peter must warn Sam of known dangers (a broken step Peter knows about) but doesn’t owe the same proactive inspection duty he’d owe a paying customer.

Judge Learned Hand’s formula offers an economic lens on breach: a precaution should be taken when its burden (B) is less than the probability (P) of harm multiplied by its severity (L) — B < PL. Failing to take a cheap, easy precaution against a serious, likely harm looks unreasonable; skipping an expensive precaution against a minor, unlikely harm may not.

United States v. Carroll Towing Co. is the actual case the formula comes from — Judge Learned Hand articulated B < PL for the first time deciding it. A barge broke loose in New York Harbor and sank, partly because its bargee wasn’t aboard during working hours to respond when other vessels bumped it loose. Hand reasoned that whether leaving the barge unattended was negligent depended on comparing the burden of having someone aboard against the probability of an accident and the severity of harm if one occurred — reducing what had been a fairly vague “reasonableness” inquiry into something courts could reason through more concretely, even if never truly reduced to pure arithmetic in practice.

Example. Peter’s store could install a cheap non-slip mat (low burden) at the entrance during rainy weather, when slip-and-fall risk is genuinely high (high PL) — failing to do so looks like a breach. Now compare: requiring Peter to completely rebuild his entire entrance at massive cost (high burden) to address a vanishingly rare, minor risk (low PL) would not be required under the same formula.

Negligence per se substitutes a statutory violation for the ordinary breach analysis, when the plaintiff is in the statute’s protected class and the harm is the type it was designed to prevent. Res ipsa loquitur lets a jury infer negligence from an accident that ordinarily wouldn’t happen absent negligence, where the relevant instrumentality was in the defendant’s exclusive control.

Byrne v. Boadle is the real, original case behind the falling-barrel example below — res ipsa loquitur’s founding case. A barrel of flour rolled out of a second-story warehouse window and struck a passerby on the street; no one saw exactly what happened inside, and the plaintiff had no way to prove specifically what the warehouse workers did wrong. The court allowed the case to proceed anyway: barrels simply don’t ordinarily fall out of warehouse windows unless someone was careless, and since the warehouse and its contents were in the defendant’s exclusive control, the accident itself was enough to let a jury infer negligence, without the plaintiff needing to prove the specific careless act.

Example. A statute requires stairwell handrails specifically to prevent falls; Peter’s building lacks one, and John falls and is injured because there was nothing to grab — negligence per se, since all three elements (violation, protected class, matching harm type) line up. Now compare a different case with no relevant statute at all: a barrel of flour falls from Peter’s warehouse window and injures a passerby below — res ipsa loquitur may apply instead, since barrels don’t ordinarily fall from windows absent someone’s negligence, and the warehouse was in Peter’s exclusive control.

The but-for test asks: would the harm have occurred but for the defendant’s negligent conduct? When multiple independent causes would each have been sufficient alone (like two merging fires), the substantial factor test is used instead, since a strict but-for analysis would let each defendant escape by pointing to the other.

Summers v. Tice handles a related but different problem: two negligent defendants, only one of whom actually caused the harm, with no way to tell which. Two hunters, hunting quail together, both negligently fired in the plaintiff’s direction at essentially the same moment; one shotgun pellet hit the plaintiff’s eye, but medical evidence couldn’t determine which hunter’s shot actually caused it. Rather than let the plaintiff recover nothing simply because both defendants could each point to the other and say “maybe it was him,” the court shifted the burden to the two negligent defendants to prove they weren’t the actual cause — since both were unquestionably negligent and only their own conduct created the genuine uncertainty, it was fairer to make them sort it out than to leave an innocent plaintiff with nothing.

Example. But for Peter’s uncleared ice, John would not have slipped — a clean but-for case. Now compare: Peter and a second, unrelated party each independently start a fire, and both fires merge and would each alone have destroyed the warehouse — the substantial factor test holds each of them liable, since a strict but-for test would absurdly let both escape by pointing to the other’s independently sufficient fire.

Proximate cause is a policy-driven limit on liability — even with actual cause satisfied, was the harm a reasonably foreseeable result? A superseding cause — a sufficiently unforeseeable, independent intervening event — can break the chain and cut off liability for what happens after it. The eggshell skull rule means a defendant remains liable for the full extent of harm even if an unusual vulnerability made it far worse than typically expected.

Palsgraf v. Long Island Railroad Co. is the single most famous case in American tort law, and it’s really about proximate cause dressed up as a duty question. A railroad guard helped a passenger board a moving train, dislodging a package the passenger was carrying — unknown to anyone, it contained fireworks, which exploded on the platform. The shock of the explosion caused scales at the far end of the platform to fall, injuring Mrs. Palsgraf, who was standing nowhere near the incident itself. Writing for the majority, Judge Cardozo held the railroad owed her no duty at all: negligence toward one person (the passenger with the package) doesn’t automatically create liability to an entirely different, unforeseeable plaintiff outside the zone of danger the conduct actually created — you can only be negligent toward someone the risk was reasonably directed at in the first place, however real the ultimate injury.

Example. John, injured by Peter’s negligence, needs an ordinary ambulance ride to the hospital — a foreseeable consequence, within Peter’s scope of liability. Now compare: on the way, a wildly reckless, unrelated driver runs a red light and crashes into the ambulance, causing additional injuries — a serious candidate for a superseding cause, genuinely contestable, since that specific reckless intervening act may be independent and unforeseeable enough to cut off Peter’s liability for the crash injuries specifically (though not for the original injury either way).