In tort law, intervening and superseding causes are the doctrines courts use to decide whether a later event breaks the link between a defendant’s negligence and the plaintiff’s injury. An intervening cause is any new event that enters the chain after the defendant’s negligent act. A superseding cause is an intervening cause so unforeseeable and extraordinary that it replaces the original negligence as the legal cause of harm, cutting the defendant loose from liability. Almost every fight over these doctrines comes down to a single question: was the later event foreseeable?
The Core Difference
Every intervening event is a candidate for superseding status, but very few qualify. When someone’s negligence sets an injury in motion, they are generally responsible for the full result even if other events pile on along the way. That responsibility breaks down only when a later event is so disconnected from the original negligence that holding the first actor liable no longer makes sense.
Think of it as a chain. The defendant’s negligent act is the first link. Everything that happens afterward adds links. An ordinary intervening cause is a link that fits the chain; a superseding cause is a break so sharp the chain can’t carry weight across it. The test for the break is foreseeability, not timing or severity.
This matters because proximate cause is part of the plaintiff’s case from the start. A defendant arguing that a superseding event cut the chain isn’t raising a separate affirmative defense. The defendant is arguing that the plaintiff hasn’t shown the injury flowed from the negligent act in a natural and continuous sequence.
Dependent and Independent Intervening Forces
Courts sort intervening causes into two categories, and the category usually tells you the answer.
A dependent intervening force is a response triggered directly by the defendant’s negligence. A bystander pulling an injured person from a car wreck. A doctor treating accident injuries. A driver swerving to avoid debris the defendant left in the road. These actions arise as natural reactions to the situation the defendant created, so courts treat them as foreseeable almost by default. A dependent intervening force rarely breaks the causal chain unless the response is wildly abnormal.
An independent intervening force operates on the situation the defendant created but isn’t a direct response to it. A lightning strike during a rescue. A separate criminal attack on an already-injured plaintiff. Whether an independent force breaks the chain depends entirely on how foreseeable it was. A second car hitting someone lying in the road after a first collision is independent but foreseeable, so the first driver stays on the hook. A tornado touching down at the accident scene is independent and extraordinary, and it probably breaks the chain.
The categories aren’t a formality. They give courts a structured way to think about what the defendant should have anticipated: dependent forces get a strong presumption of foreseeability, and independent forces get evaluated case by case.
When an Intervening Cause Becomes Superseding
The Restatement (Second) of Torts identifies several factors courts weigh when deciding whether an intervening force rises to the level of a superseding cause:
- Whether the intervening force operated independently of the situation the defendant created
- Whether the result was abnormal or extraordinary
- Whether a reasonable person would have anticipated the force
- Whether the intervening actor exercised their own independent judgment
No single factor controls. Courts look at the full picture and ask whether holding the original defendant responsible still makes sense.
A concrete contrast helps. If a negligent driver causes a collision and a second driver rear-ends the stopped cars while rubbernecking, that second collision is intervening but almost certainly foreseeable, and the first driver remains liable. But if the collision produces only a minor fender-bender and, while the drivers exchange insurance information, a small plane crashes into the intersection, no reasonable person would have predicted it. The plane crash is a superseding cause.
Criminal Acts by Third Parties
Criminal acts by strangers are the strongest candidates for superseding cause status. Courts generally treat them as unforeseeable because the law doesn’t expect people to anticipate that a third party will choose to commit a crime. When a completely independent criminal act produces the plaintiff’s injury, the original defendant’s negligence fades into the background.
The major exception arises when the defendant’s negligence specifically created the opportunity for the criminal conduct. A property owner who ignores a broken security gate in a neighborhood with a documented history of break-ins can’t hide behind the superseding cause defense when a tenant gets robbed. The criminal act was foreseeable precisely because the defendant’s failure to maintain security invited it. Courts evaluate local conditions, prior incidents, and the nature of the security failure to decide whether the crime was a predictable consequence of the negligence.
Medical Errors After the Original Injury
When someone gets hurt and seeks medical treatment, the original defendant generally stays liable for harm caused by ordinary medical errors during that treatment. It’s foreseeable that an injured person will need medical care, and it’s foreseeable that medical care sometimes involves mistakes. Seeking treatment is a textbook dependent intervening force.
This rule extends further than many people expect. Where a plaintiff exercises reasonable care in choosing a competent doctor and following medical advice, the law treats the original negligent act as the proximate cause of damages flowing from subsequent negligent treatment. The first defendant doesn’t get a discount because a nurse made an error or a surgeon had a bad day. The injured person wouldn’t have been on the operating table at all if not for the defendant’s negligence.
The line shifts only when the medical error is so extreme and unusual that it can’t be considered a normal risk of treatment. A surgeon operating on the wrong limb or performing a completely unrelated procedure falls outside what anyone would anticipate. In those rare cases, the medical error is extraordinary enough to qualify as a superseding cause.
Acts of Nature
Weather and natural events sit on a sliding scale of foreseeability. Rain, wind, seasonal storms, and temperature swings are ordinary conditions that people encounter routinely, and a defendant is expected to account for them. If a building collapses during a moderate storm because of shoddy construction, the builder can’t blame the weather. The storm was foreseeable; the real cause was the negligent construction.
The analysis flips only when the natural event is truly extraordinary. A catastrophic earthquake in a region with no seismic history, or a flood so extreme it exceeds any recorded precedent, can qualify as a superseding cause. Courts apply the “act of God” defense narrowly. The natural force must be entirely independent of human activity, inevitable in the sense that no precaution could have prevented it, and of a character that historical conditions in the area gave no reasonable warning of. Heavy rainfall alone usually doesn’t qualify, even if it’s heavier than usual, because rain is inherently foreseeable in most places.
Rescuers and the Rescue Doctrine
A defendant who negligently creates a dangerous situation should expect that someone will try to help. The rescue doctrine holds that a rescuer’s intervention is a foreseeable response to the defendant’s negligence, not a superseding cause. If a bystander gets hurt pulling someone from a burning car after the defendant caused the crash, the defendant is liable for the rescuer’s injuries too. Danger invites rescue.
The doctrine applies to ordinary bystanders who act reasonably under the circumstances. A rescuer who takes reckless or wildly disproportionate risks might fall outside the doctrine’s protection, because at some point the rescue attempt itself becomes the dominant cause of the rescuer’s injuries.
Professional rescuers face a different standard. Under the professional rescuer rule (sometimes called the fireman’s rule), firefighters, police officers, and other professional rescuers generally cannot sue the person whose negligence created the emergency they were called to handle. The rationale is that they voluntarily chose careers involving known hazards and are compensated for assuming those risks. The rule has limits: professional rescuers can still recover for injuries caused by risks independent of the emergency they responded to, such as a collapsing staircase in a burning building the owner negligently failed to maintain. Courts also carve out exceptions when the defendant’s conduct rises to recklessness or gross negligence.
The Modern Scope-of-Liability Approach
The traditional superseding cause framework still dominates in most courtrooms, but tort law is moving. The Restatement (Third) of Torts, published in 2010, abandoned the language of “superseding cause” entirely. In its place, the Third Restatement uses a scope-of-liability test: a defendant is liable for harms that result from the risks that made the defendant’s conduct negligent in the first place.
The practical difference is subtle but real. Under the traditional framework, courts focus on the intervening event and ask whether it was foreseeable. Under scope-of-liability, courts focus on the type of harm and ask whether it falls within the range of risks the defendant’s negligence created. A distracted driver creates the risk of collisions. If the collision leads to a fire because the other car’s gas tank was poorly designed, the distracted driver is still liable because fire-related injuries fall within the general risk of collisions. If the collision somehow triggers a chain of events ending in a completely unrelated type of harm, liability stops.
The Third Restatement reaches many of the same results as the traditional framework, but it reframes the question in a way some courts find cleaner. Anyone raising or defending against a superseding cause argument should know which framework their jurisdiction follows, because the framing can influence how a jury thinks about the case.
Who Proves What
Proximate cause is an element of the plaintiff’s case, not an affirmative defense. The plaintiff carries the initial burden of showing that the defendant’s negligence was a proximate cause of the injury. A defendant arguing superseding cause is really arguing that the plaintiff hasn’t met this burden.
That distinction has procedural weight. A defendant doesn’t need to plead “superseding cause” as an affirmative defense in the answer to preserve the argument. The defendant can challenge proximate cause at summary judgment or at trial by presenting evidence that an unforeseeable intervening event, not the defendant’s negligence, was the actual legal cause of the harm.
Whether an intervening event qualifies as superseding is almost always a question for the jury. The judge decides whether there’s enough evidence for the issue to go to the jury, but the jury weighs how unusual the event was, whether it was foreseeable, and whether the defendant’s negligence still played a meaningful role in producing the harm. Only in clear-cut cases, where no reasonable juror could disagree, will a court resolve the question as a matter of law.
When the Chain Holds: Shared Fault
When an intervening cause is foreseeable and doesn’t rise to superseding, both the original defendant and the intervening actor may share liability. How that plays out depends on the jurisdiction.
Most states use some form of comparative fault, which reduces recovery based on each party’s percentage of responsibility. A plaintiff found 30% responsible for a $100,000 loss recovers $70,000. The majority of states use a modified system that bars recovery entirely once the plaintiff’s share of fault hits 50% or 51%, depending on the state. A smaller number use a pure system that allows recovery no matter how large the plaintiff’s share, reducing the award proportionally even if the plaintiff was 90% at fault.
When multiple defendants share responsibility for an indivisible injury, joint and several liability may apply. Each defendant is independently liable for the full amount of damages, meaning a plaintiff can collect the entire judgment from whichever defendant has the deepest pockets, and that defendant then seeks contribution from the others. Many states have modified or limited joint and several liability in recent decades, so availability varies significantly.