Legal Disclaimer: This article provides general legal information only. Laws vary by jurisdiction, and individual circumstances differ substantially. Consult a licensed attorney in your state for advice specific to your situation.
Two Causation Questions
Proving negligence requires more than showing the defendant breached their duty. The plaintiff must also prove that breach caused their injuries. Courts split this inquiry into two distinct questions: actual cause (also called cause-in-fact) and proximate cause (also called legal cause).
Both must be satisfied. A breach with no actual causal connection fails. A breach that actually caused harm but was too remote to be legally recognized also fails. Understanding the distinction is critical for anyone involved in car accident litigation.
Actual Cause: The But-For Test
Actual cause asks a factual question: did the defendant’s conduct actually contribute to the plaintiff’s injury? The standard test is the “but-for” test. But for the defendant’s negligent act, would the injury have occurred?
Consider a driver who runs a red light and strikes a vehicle lawfully proceeding through an intersection. But for running the red light, the defendant would not have entered the intersection at that moment, and the collision would not have occurred. Actual cause is established.
The but-for test works well when a single negligent act leads to a clear result. It becomes complicated when multiple causes contribute. If two cars both run a red light and collide, each driver’s negligence was a but-for cause of the other’s injuries.
Substantial Factor Alternative
When multiple causes make but-for analysis awkward, courts sometimes apply the “substantial factor” test instead. Was the defendant’s conduct a substantial factor in bringing about the harm? This test avoids the logical problem of two independent causes, either of which alone would have been sufficient.
Most car accident cases do not require substantial factor analysis because the but-for test works clearly. But multi-vehicle pileups and concurrent negligence scenarios sometimes demand it.
Proximate Cause: The Foreseeability Limit
Proximate cause asks a legal question: should the defendant be held responsible for this particular consequence? Even if the defendant’s breach actually caused harm in the but-for sense, liability may not follow if the harm was too remote, too unusual, or too unforeseeable.
Courts describe proximate cause using language like “natural and continuous sequence” and “foreseeable consequences.” A defendant is liable for harms that a reasonable person would anticipate might result from their negligent conduct.
A driver who rear-ends another vehicle can foresee that the collision might cause whiplash, broken bones, or vehicle damage. Those consequences flow naturally from the breach. But if the collision somehow triggers a gas station explosion two miles away that injures a bystander, proximate cause likely fails. The chain of events is too attenuated.
Foreseeability in Application
Foreseeability does not require predicting the exact injury. A driver who runs a red light need not foresee that the specific victim would be in the intersection at that precise moment. General foreseeability suffices: running red lights creates foreseeable risk of collision with crossing traffic.
Similarly, the type of injury need not be precisely anticipated. Foreseeing that a collision might cause injury is enough; the defendant need not predict the specific fracture or soft tissue damage that results.
The Eggshell Plaintiff Rule
One critical exception to foreseeability limits: the eggshell skull rule. A defendant takes their victim as they find them. If the plaintiff had a pre-existing condition that made them unusually vulnerable, the defendant is liable for the full extent of injury, not just what would have happened to an average person.
A plaintiff with a degenerative spinal condition may suffer permanent paralysis from a collision that would only have caused temporary whiplash in a healthy person. The defendant cannot escape liability by arguing the severe outcome was unforeseeable. The collision was foreseeable; the specific severity is irrelevant.
This rule prevents defendants from benefiting from their victim’s vulnerabilities. It also means liability exposure can be vastly greater when the plaintiff happens to have pre-existing fragility.
Superseding Cause: Breaking the Chain
A superseding cause is an intervening event that breaks the chain of proximate causation. If a new, independent act intervenes between the defendant’s breach and the plaintiff’s injury, that intervening act may absorb liability.
The intervening act must be unforeseeable and independent to qualify as superseding. If a defendant causes a minor fender-bender and then a third party comes along and commits an intentional assault on the plaintiff, that assault is a superseding cause. The original defendant is not liable for assault injuries.
However, foreseeable intervening acts do not break the chain. If a defendant leaves an accident scene and the plaintiff, now stranded on a highway shoulder, is struck by another vehicle, that second collision may be foreseeable. The original defendant could remain liable.
Medical Malpractice as Intervening Act
A common scenario: the defendant causes a crash, the plaintiff goes to the hospital, and negligent medical treatment worsens the injuries. Generally, negligent medical care is foreseeable when someone is injured and seeks treatment. Courts typically hold that medical malpractice does not break the causal chain; the original tortfeasor remains liable for all injuries flowing from the crash, including those aggravated by medical negligence. The plaintiff may also have a separate claim against the medical provider.
Proving Causation in Practice
Expert Testimony
Accident reconstruction experts analyze physical evidence to determine how a crash occurred and what role each party’s conduct played. They interpret skid marks, vehicle damage patterns, EDR data, and physics models to establish causation.
Medical experts connect injuries to the collision. Defense attorneys frequently argue that plaintiff injuries predated the crash or resulted from something else. Medical causation testimony rebuts these defenses.
EDR and Physical Evidence
Event Data Recorders capture pre-crash vehicle data, providing objective evidence of speed, braking, and steering. This data often resolves causation disputes that would otherwise depend on conflicting witness accounts.
Crush analysis, glass breakage patterns, and debris fields reconstruct the collision sequence. Physical evidence does not lie, though interpretation requires expertise.
Causation Disputes: Common Defense Strategies
Pre-Existing Conditions
Defendants often argue that the plaintiff’s injuries resulted from conditions that existed before the crash. Medical records from before and after the collision become central evidence. Comparative MRI analysis can show whether disc herniations or other structural damage predated the accident.
Alternative Causes
The defense may argue that something else caused the injury: a subsequent accident, a workplace incident, or a recreational activity. Plaintiffs must show the defendant’s breach was the cause, not an alternative explanation.
Lack of Impact Correlation
In minor impact crashes, defendants argue that the collision forces were too low to cause the claimed injuries. Biomechanical experts testify about crash forces and human injury thresholds.
Key Takeaways:
Actual cause uses the but-for test to establish factual connection between breach and injury. Proximate cause limits liability to foreseeable consequences, cutting off claims that are too remote or unusual. The eggshell plaintiff rule makes defendants liable for the full extent of injury regardless of the victim’s unusual vulnerability. Superseding causes break the chain, but only when the intervening act is unforeseeable and independent.
Sources:
- But-for test and substantial factor alternative: Restatement (Second) of Torts § 431-432
- Eggshell plaintiff rule: Womack v. Crow and related case law
- Proximate cause and foreseeability: Standard jury instructions in civil negligence cases