⚡ 10-Second Rule
Erase the careless act in your head — if the harm disappears with it, the act was an actual cause.
🧒 ELI-10 Scene
Nina leaves the garden hose running into the basement window. Erase her mistake, and the basement stays dry. Her hose caused the flood. Now suppose Tom also left his hose running into the same window. Either hose alone would have soaked the carpet. Each kid says, "Erase me — the flood happens anyway!" That answer feels like a cheat, so we change the question. Was each hose a big, real part of the flood? Yes. Both kids are on the hook. Last one: Ava and Ben each hurl a snowball at the garage. One snowball cracks the window, but nobody knows whose. Since both threw carelessly, each must prove "not mine" — or both pay.
⚖️ Actual Rule
The default test is but-for causation: the defendant's tortious conduct is a factual cause of harm when the harm would not have occurred absent that conduct (paraphrasing Restatement (Third) of Torts: Liability for Physical and Emotional Harm § 26).
When multiple forces combine, but-for still works if neither act alone was sufficient — each careless act remains a but-for cause of the combined harm. But when two or more forces are each independently sufficient to cause the entire harm, mechanical but-for analysis would absolve everyone. Courts instead hold each sufficient force a factual cause — often phrased as asking whether each was a substantial factor in producing the harm (paraphrasing Restatement (Second) of Torts § 432(2) and Restatement (Third) of Torts: Liability for Physical and Emotional Harm § 27) — the rule of the merged-fires cases such as Anderson v. Minneapolis, St. Paul & Sault Ste. Marie Railway, 146 Minn. 430, 179 N.W. 45 (1920).
Under alternative liability, when two or more defendants act negligently but only one unidentifiable actor caused the harm, the burden shifts to each defendant to prove he did not cause it; if none can, all are liable. Summers v. Tice, 33 Cal. 2d 80 (1948) (two hunters, one pellet); the principle is restated in Restatement (Second) of Torts § 433B(3).
Loss of chance: in medical malpractice, some courts allow a patient whose pre-negligence odds of survival were already below fifty percent to recover for the lost chance itself, with damages usually discounted in proportion to the chance destroyed. Jurisdictions split; under strict traditional but-for preponderance analysis such a plaintiff loses. Flag the doctrine, state the split, and apply but-for unless the question invites the exception. [NJ-VARIANT: flagged for future Eli Explains NJ Law module]
ELI-10 translation: ask if the harm vanishes when you erase the mistake — and when two big causes each could have done it alone, or the true culprit is hidden among careless actors, use the special backup rules instead.
🔍 Ask These Questions
- Apply but-for first: erase the careless act — does the same harm still happen? (Rewind the movie without the mistake and watch the ending.)
- Did two combined causes each contribute, with neither enough alone? (Two small leaks that flood only together are both but-for causes.)
- Were there two or more forces each sufficient alone? Drop but-for; ask if each was a substantial factor. (When either hose alone floods the basement, both hose-leavers pay.)
- Multiple careless actors but only one unknown culprit? Shift the burden to the defendants. (Both snowball throwers must prove "not mine.")
- Is it a medical case with under-50% survival odds? Flag loss of chance and the jurisdictional split. (Some courts pay for the destroyed chance, sliced to its size.)
- Causation found? Remember factual cause is only half the causation story. (You still must ask whether the harm was the predictable kind — that's the next lesson.)
⚠️ Bar Trap
Exam language: Examiners present two independently sufficient causes — two fires, two polluters, two crushing forces — and offer the answer "no liability, because the harm would have occurred regardless of the defendant's conduct." Choosing it applies but-for mechanically where the multiple-sufficient-causes rule controls. A second bait mislabels these facts as Summers v. Tice burden-shifting, which fits only when just one unidentified actor caused the harm.
ELI-10: When two causes each could have done the whole job, "it would have happened anyway" is the trap answer. And the prove-it-wasn't-me rule is only for whodunits — not for cases where both actors clearly did damage.
🧪 Question
Two chemical plants sit upstream of a commercial fish hatchery on opposite banks of a river. On the same night, each plant independently and negligently released a solvent into the river. Undisputed expert testimony established that each release, by itself, contained more than enough solvent to kill every fish in the hatchery, and that the two plumes reached the hatchery within minutes of each other. All the fish died. The hatchery owner sued the first plant, which moved for judgment on the ground that its release could not be a factual cause of the loss.
Should the court deny the plant's motion?
(A) No, because the fish would have died from the second plant's release even if the first plant had released nothing. (B) No, unless the owner can establish which plant's solvent reached the hatchery first. (C) Yes, because the first plant's release was an independently sufficient force and thus a substantial factor in killing the fish. (D) Yes, because the burden shifts to each plant to prove that its solvent did not cause the deaths.
Answer: (C). With two negligent releases each sufficient to destroy the entire stock, the multiple-sufficient-causes rule treats each as a factual cause; the first plant cannot hide behind the other's equal wrong.
💡 Why the Wrong Answers Are Wrong
- (A) applies but-for mechanically to independently sufficient causes — the precise situation the substantial-factor rule exists to fix.
- (B) demands proof of arrival order that the doctrine makes irrelevant; each sufficient plume is a cause regardless of which touched the fish first.
- (D) invokes Summers v. Tice burden-shifting, which applies when only one unidentified defendant caused the harm — here both releases contributed to a common destruction.
- ELI-10: The misconception is thinking "it would have happened anyway" always wins. When each careless act could have wrecked everything alone, the law refuses to let both wrongdoers point at each other.
