Factual Causation: The Counterfactual That Changes with Two Fires
Actual causation asks whether the defendant’s conduct factually produced the plaintiff’s harm, while proximate causation asks whether that harm falls within the conduct’s foreseeable scope of risk. These are separate gates: a defendant may be a factual cause without being a proximate cause, and a foreseeable risk cannot matter unless the conduct actually contributed to the injury.
For but-for causation, identify the specific negligent conduct and ask whether the plaintiff would have suffered the same harm without it. If the answer is no, the conduct is an actual cause. If the plaintiff would have suffered the same harm anyway because another force would independently have produced it, the but-for test is not satisfied.
Run the test precisely:
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Define the harm being attributed to the defendant. Do not ask whether the defendant generally created a dangerous situation; ask whether the challenged conduct produced this injury or loss.
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Remove the conduct from the facts while holding the other conditions constant.
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Ask whether the harm would still have occurred. If it would not, but-for causation exists. If it would, ordinary but-for causation fails.
Two or more causes can be multiple necessary causes. Each cause is necessary when the harm would not have occurred without that cause, even though no single cause was sufficient by itself. For example, two negligent drivers collide with a pedestrian at nearly the same time. If each driver’s impact was needed to produce the pedestrian’s broken pelvis, each driver’s conduct satisfies the but-for test. The fact that neither driver alone would have caused the full injury does not defeat actual causation.
The difficult variation is multiple sufficient causes. Each force is independently sufficient to produce the same harm, but both forces actually operate. Two separate fires may each be capable of destroying a warehouse, and each may reach the warehouse. Removing either fire from the facts still leaves the other fire capable of causing the destruction, so but-for reasoning would incorrectly deny causation for both fires.
For that pattern, apply the substantial factor test: each defendant’s conduct is an actual cause if it was a substantial factor in bringing about the harm. The conduct must have made a meaningful contribution to the injury; a merely trivial or purely background condition is not enough. The test prevents the but-for test from producing a false negative when independent causes each would have been sufficient.
| Causation question | But-for test | Substantial factor test |
|---|---|---|
| Trigger | Each cause was necessary to produce the harm | Each independent cause was sufficient by itself |
| Counterfactual | Would the harm occur without this conduct? | Did this conduct meaningfully contribute to the harm? |
| Typical pattern | Two forces combine, and neither alone is enough | Two forces each independently can produce the harm |
| Result | No answer means no actual cause | A substantial contribution establishes actual cause despite but-for failure |
Do not use the substantial-factor test merely because several events appear in the story. First determine whether the causes are necessary or independently sufficient. If each was needed, use but-for causation. If each alone would have been enough, use substantial-factor analysis. This is closed-book: be able to state each test, its trigger, and its consequence without legal materials.
Actual causation also requires distinguishing a cause from a condition. A defendant’s conduct need not be the only cause, the greatest cause, or the immediate cause. It must be part of the factual sequence that produced the injury. But a fact that merely made the injury possible, while making no meaningful contribution to the injury that occurred, is not enough.
Scope of the Risk: When a Factual Cause Also Counts Legally
After actual causation, apply the scope-of-the-risk test for proximate cause. Identify the risk that made the defendant’s conduct negligent, then compare that risk with the type of harm the plaintiff suffered. If the harm resulted from the same general kind of danger, it is foreseeable and falls within the scope of the risk. If it resulted from an entirely different kind of danger, proximate causation is absent even though the conduct was a but-for cause.
The analysis is executable:
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State the risk created by the defendant’s conduct in general terms. The question is not whether the defendant could predict every detail, but what kind of harm made the conduct dangerous.
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Identify the type of harm that occurred.
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Ask whether the actual harm is a foreseeable manifestation of that risk.
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If yes, proximate causation ordinarily exists. If no, the causal chain ends for that harm.
Foreseeability concerns the type of harm, not its precise mechanics. A defendant need not foresee the exact sequence of events, the exact person injured, the exact instrumentality, or the exact timing. If negligent driving creates a foreseeable risk of a collision, the defendant may be liable even if the collision occurs through an unusual chain of impacts. If careless conduct creates a foreseeable fire risk, an unusual route by which the fire spreads does not necessarily take the loss outside the risk.
The near-miss is a different kind of harm. If the defendant’s conduct created a risk of physical injury but the plaintiff suffers a wholly unrelated economic or emotional consequence that is not a manifestation of that physical danger, foreseeability may fail. The inquiry is not whether the defendant’s conduct was somehow connected to the plaintiff’s loss; it is whether the loss is the kind of harm that made the conduct unreasonable.
Do not confuse unforeseeable severity with unforeseeable type. Under the eggshell-plaintiff rule, once the type of injury is within the scope of the risk, the defendant is liable for the full extent of the injury even if the plaintiff’s unusual fragility makes the injury much more serious than an ordinary person’s injury. A fragile plaintiff who suffers catastrophic consequences from a foreseeable physical impact does not convert a foreseeable injury into an unforeseeable type of harm.
An event after the defendant’s conduct may be an intervening cause if it contributes to the final harm. Timing alone does not make an event intervening: the later event must actively play a causal role. An intervening cause may be foreseeable or unforeseeable.
A superseding cause is an unforeseeable intervening cause that is sufficiently abnormal or extraordinary to break the causal chain and relieve the defendant of liability for the later resulting harm. Thus, the terms are not interchangeable:
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Every superseding cause is intervening.
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Not every intervening cause is superseding.
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A foreseeable intervening cause ordinarily does not supersede.
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An unforeseeable and extraordinary intervening cause ordinarily does supersede.
Responsive intervening events are generally foreseeable because they are normal reactions to the danger the defendant created. A person may attempt to escape a danger, a bystander may attempt a rescue, or an injured person may seek medical treatment. Negligent medical treatment is ordinarily foreseeable and therefore is usually intervening but not superseding. Extraordinary or grossly negligent treatment may be sufficiently unforeseeable to supersede.
Coincidental events are not responses to the defendant’s danger. A third party’s criminal act or an extraordinary natural event is more likely to be superseding. But intentional or criminal conduct is not automatically superseding. If the defendant’s negligence created the very opportunity or risk of that kind of misconduct, the misconduct may fall within the scope of the risk and remain a foreseeable intervening cause.
| Later event | Ordinary characterization | Usual causal consequence | Boundary |
|---|---|---|---|
| Ordinary negligent medical treatment | Responsive intervening cause | Usually not superseding | Gross or extraordinary malpractice may supersede |
| Rescue or escape attempt | Responsive intervening cause | Usually not superseding | An extraordinary and independent response may supersede |
| Third-party crime | Often coincidental intervening cause | Often superseding | Not superseding when the negligence created a foreseeable opportunity for the crime |
| Natural event | Often coincidental intervening cause | Depends on foreseeability | Ordinary expected conditions usually do not supersede; extraordinary events may |
A superseding cause does not mean the defendant’s conduct was never a factual cause. It means the later event is treated as the legal stopping point for the defendant’s responsibility for the later harm. Analyze the harm in portions when necessary: the defendant may remain liable for the injury already caused even if a later superseding event causes additional harm.
Once actual cause is established, the order matters:
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The chart’s “not superseding” result means the later event remains part of the causal chain; it does not mean the defendant automatically loses. The defendant must still have been an actual cause, and the later event must not have changed the harm into a type outside the original scope of risk.
One Causation Item: Ordinary Malpractice Does Not Break the Chain
The following item combines the scope-of-risk test with the intervening-versus-superseding distinction.
Dana negligently strikes Priya with her car, causing Priya to suffer a broken leg. At the hospital, a surgeon provides ordinary but negligent treatment that causes an infection, requiring Priya to undergo an amputation. The infection and amputation are an aggravation of the original injury, and the facts contain no gross or extraordinary malpractice.
Practice
Which is the best analysis of Dana’s responsibility for Priya’s injuries?
Recurring errors in these objectives include:
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Treating the two warehouse fires as defeating causation because neither fire passes the ordinary but-for test, instead of applying the substantial factor test for multiple sufficient causes.
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Calling every later event superseding, even though ordinary medical treatment responding to an injury is a foreseeable intervening cause.
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Requiring the defendant to foresee the exact sequence of impacts instead of asking whether the type of harm falls within the scope of the risk.
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Treating an unusually severe injury to a fragile plaintiff as an unforeseeable type of harm instead of applying the eggshell-plaintiff rule.
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Assuming every intentional act automatically supersedes, even when the defendant’s negligence created a foreseeable opportunity for that act.
Three Causation Drills: Necessary Causes and Chain-Breaking Events
Practice
Two careless drivers independently strike a pedestrian within seconds of each other. Medical evidence shows that each driver’s impact was necessary to produce the pedestrian’s fractured pelvis; neither impact alone would have caused that fracture. Which analysis best applies to each driver’s conduct?
Two independent fires reach a warehouse at the same time. One fire was caused by the defendant’s negligence, and the other was caused by lightning. Either fire alone would have destroyed the plaintiff’s inventory, and the defendant’s fire actually reached and burned the inventory. Which analysis best establishes actual causation?
A driver negligently injures a pedestrian’s leg. During ordinary negligent medical treatment, the pedestrian develops an infection that makes the injury much more severe. Which statement best describes the medical treatment?
High-Yield Points - ⚡ Biggest Takeaways
Use but-for for necessary causes and substantial factor for independently sufficient causes. Proximate cause asks whether the harm is a foreseeable type within the risk that made the conduct dangerous. An intervening cause breaks the chain only when it is sufficiently unforeseeable and extraordinary to be superseding.
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