In personal injury law, proximate cause is the rule courts use to decide whether a defendant’s conduct is connected closely enough to your injury to make them legally responsible for it. It works as a limit on liability. Even when someone’s careless act set the harm in motion, the law will not hold them financially responsible unless the injury was a reasonably foreseeable consequence of what they did. Without that limit, a single moment of carelessness could stretch liability out to an endless chain of consequences, and courts refuse to go that far.
Two Causation Questions, Not One
Winning a negligence claim requires proving two separate kinds of causation, and each does different work.
The first is cause-in-fact. This is a factual question: did the defendant’s conduct actually contribute to the injury? The second is proximate cause, which is a policy question: is the connection between that conduct and the injury close enough that the law should treat the defendant as responsible?
You have to clear both. An act can be the factual cause of an injury and still not create liability, because the harm was too remote, too strange, or too far removed from anything the defendant could have anticipated. Proximate cause is the filter that separates consequences a person should answer for from those the law treats as beyond their reach.
How Courts Test the Factual Link
Cause-in-fact is usually measured with the but-for test. The question is simple: would the injury have happened if the defendant had not acted the way they did? If the answer is no, cause-in-fact is established.
A driver runs a red light and hits a pedestrian crossing legally in a crosswalk. The pedestrian would not have been struck but for the driver running the light. Cause-in-fact is satisfied. Whether proximate cause is also satisfied is a separate analysis.
The but-for test breaks down when two independent forces each would have been enough to cause the injury on their own. If two factories independently dump enough toxins into a river to poison it, each one can argue the contamination would have happened anyway because the other’s discharge alone was sufficient. Under a strict but-for reading, neither factory caused the harm, which is an absurd result.
Many jurisdictions solve this with the substantial factor test. Instead of asking whether the harm would have occurred without the defendant’s conduct, the court asks whether the defendant’s conduct was a significant contributing factor. If it was more than trivial, the defendant is on the hook, even where another party’s conduct independently would have produced the same result. That approach allows courts to hold multiple defendants jointly liable when their separate acts converge to produce a single injury.
Foreseeability Is the Heart of Proximate Cause
Once cause-in-fact is established, the real question becomes whether the injury was foreseeable. Foreseeability does not mean the defendant had to predict the exact sequence of events. It means a reasonable person in the defendant’s position should have recognized that their conduct created a risk of the general type of harm that occurred.
If a construction crew leaves an unmarked hole in a sidewalk, it is foreseeable that someone will fall in and break a bone. The crew does not have to foresee which pedestrian will fall or exactly how they will land. The general risk of a fall injury is obvious, and that is enough to make the crew’s negligence a proximate cause.
The Palsgraf Case
The classic illustration is Palsgraf v. Long Island Railroad Co., a 1928 New York Court of Appeals decision that shaped how American courts think about foreseeability. Helen Palsgraf was standing on a train platform when railroad employees helped a rushing passenger board a moving train. They accidentally knocked loose a package the man was carrying. The package turned out to contain fireworks. It hit the tracks, exploded, and the blast toppled a heavy scale at the far end of the platform, which struck and injured Palsgraf.
Judge Cardozo, writing for the majority, ruled that the railroad owed no duty of care to Palsgraf because her injury was not foreseeable. The employees had no way to know the package contained explosives, and even if helping the passenger aboard was careless, the risk of injuring someone far down the platform through a chain of explosions and falling objects was not within the range of danger their conduct created. The decision established that liability extends only to people foreseeably within the zone of risk.
The Eggshell Skull Rule
Foreseeability governs the type of harm a defendant can be held liable for, but not the extent. This catches a lot of defendants off guard.
Under the eggshell skull rule, a defendant who causes a foreseeable type of injury is responsible for its full severity, even if the plaintiff’s pre-existing condition made the harm far worse than anyone could have expected. You take your victim as you find them. Rear-end someone at low speed in a collision that would normally cause minor whiplash, and if the driver you hit has a spinal condition that turns it into a serious injury, you are liable for the full extent of the damage.
This might look like a contradiction, but courts draw a clear line. Proximate cause requires that the general type of harm be foreseeable. A car collision foreseeably causes physical injury, so physical injury is within the scope of liability. The law does not require that the specific severity be foreseeable. As long as the defendant’s negligence proximately caused some version of the harm, the defendant bears the cost of whatever that harm turned out to be.
Intervening and Superseding Causes
Other events happen between a negligent act and the final injury, and courts have to decide whether those later events let the original defendant off the hook. These in-between occurrences are called intervening causes, and their effect on liability depends on whether they were foreseeable.
When the Intervening Event Was Foreseeable
If the intervening event was a predictable consequence of the original negligence, the chain of causation stays intact. Medical treatment is the classic example. When a negligent driver causes a car accident and the injured person receives substandard medical care that makes the injury worse, the original driver typically remains liable for the full harm. It is foreseeable that an injured person will need treatment, and foreseeable that treatment sometimes goes wrong.
When the Intervening Event Breaks the Chain
An unforeseeable intervening event, called a superseding cause, breaks the chain. When something so extraordinary and disconnected occurs that the original defendant could not have reasonably anticipated it, liability stops with the earlier actor. If an ambulance transporting a crash victim is struck by a falling tree in a freak windstorm, the original driver’s liability likely does not extend to injuries caused by the tree.
Third-party criminal acts sit in a middle ground. Courts generally presume that a stranger’s intentional crime is unforeseeable and therefore superseding. Two exceptions matter. First, if the defendant had a special relationship with the victim, like a landlord or business owner responsible for security, a criminal attack may be foreseeable where the defendant knew or should have known about the risk. Second, if the crime is among the specific dangers the defendant’s negligence created, it will not be treated as superseding. A bar that keeps serving a visibly intoxicated and aggressive patron may be liable if that patron later assaults someone, because that is precisely the kind of harm overservice creates.
Who Has to Prove It
The plaintiff carries the burden. In a civil negligence case, the injured person must prove by a preponderance of the evidence that the defendant’s conduct was a proximate cause of the harm. Preponderance of the evidence means more likely than not, a much lower bar than the beyond a reasonable doubt standard used in criminal cases. The plaintiff does not need to prove that the defendant’s negligence was the only cause, just that it was a cause, and that the harm fell within the scope of foreseeable risk.
This is where many claims fall apart. Establishing that something bad happened is usually easy. Proving the specific link between the defendant’s conduct and the specific injury, and that the injury was foreseeable, requires evidence. Medical records, expert testimony, accident reconstruction, and witness statements all play a role. A plaintiff who cannot connect the dots clearly enough loses, even if the defendant was clearly careless about something.
Why It Decides Personal Injury Cases
Proximate cause is not just an academic concept. It shapes the practical outcome of every negligence claim. If you are injured and considering legal action, the strength of your proximate cause argument often determines whether a case is worth pursuing at all. A defendant’s insurance company will study the causal chain looking for gaps, alternative explanations, or superseding events that break the link between the defendant’s conduct and your injury.
The concept also explains why two people hurt in seemingly similar situations can end up with very different legal outcomes. The person whose injury flows directly and foreseeably from the defendant’s negligence has a strong claim. The person whose injury resulted from a bizarre chain of events nobody could have predicted does not, even if the defendant was genuinely negligent. Proximate cause draws that line, and where your facts fall relative to it is often the most important question in the case.