Negligence - Problems relating to causation

Learning Outcomes

This article explains how causation problems arise in negligence questions on the MBE, including:

• Identifying and clearly separating issues of duty, breach, factual causation, proximate cause, and damages in multistep exam problems.
• Distinguishing factual causation from proximate (legal) cause and applying the but-for and substantial factor tests, especially in multiple-sufficient-cause scenarios.
• Evaluating when alternative liability, joint and several liability, contribution, and indemnity apply in cases with multiple negligent defendants or indeterminate causes.
• Assessing whether intervening events—such as medical malpractice, rescue efforts, or criminal acts—are foreseeable intervening causes or superseding causes that cut off liability.
• Applying the eggshell plaintiff rule to determine the proper scope of damages when plaintiffs have pre-existing vulnerabilities or suffer unusually severe harm.
• Recognizing common MBE traps, such as plaintiff negligence that is not a factual cause, and correctly analyzing how comparative or contributory negligence interacts with causation.
• Using structured reasoning to trace the causal chain in fact patterns, determine which actors are actual and proximate causes, and identify which parties are ultimately liable for an indivisible injury.

MBE Syllabus

For the MBE, you are required to understand causation in negligence, with a focus on the following syllabus points:

• Distinguish between factual causation (but-for and substantial factor tests) and proximate cause.
• Apply the rules for causation where there are multiple sufficient or indeterminate causes.
• Recognize the effect of intervening and superseding events, including criminal acts, on liability.
• Analyze scenarios involving joint tortfeasors, alternative liability, contribution, and indemnity.
• Understand the eggshell plaintiff rule and its impact on damages, including successive injuries.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which test is most commonly used to establish factual causation in negligence?
   1. Substantial factor test
   2. "But for" test
   3. Foreseeability test
   4. Last clear chance doctrine
2. If two defendants independently cause the same harm and either act alone would have been sufficient, what is the standard for causation?
   1. Both are liable only if acting in concert
   2. Neither is liable because the harm would have occurred anyway
   3. Each is liable if their conduct was a substantial factor in causing the harm
   4. Only the first actor is liable
3. An unforeseeable criminal act by a third party occurs after a defendant’s negligence. Is the original defendant generally liable for the resulting harm?
   1. Yes, always
   2. No, because it is a superseding cause
   3. Yes, if the defendant was reckless
   4. No, unless the defendant intended the harm
4. Under the "eggshell plaintiff" rule, a defendant:
   1. Is liable only for foreseeable injuries
   2. Is liable for all injuries caused, even if the extent is unforeseeable
   3. Is not liable if the plaintiff had a pre-existing condition
   4. Can reduce damages if the plaintiff is unusually vulnerable

Introduction

Causation is a core element of negligence. In addition to duty, breach, and damages, the plaintiff must prove that the defendant’s breach both factually and legally (proximately) caused the harm.

On MBE questions, causation often supplies the hidden issue: several parties may be negligent, but only some are actual and proximate causes of the plaintiff’s injury. You must therefore:

• Separate factual causation (did this conduct actually contribute to the harm?) from
• Proximate cause (is this harm within the scope of risks that made the conduct negligent?).

Key Term: Factual Causation
The requirement that the defendant’s breach was a necessary condition for the plaintiff’s harm; usually tested by asking whether the harm would have occurred but for the defendant’s act or omission.

Key Term: Proximate Cause
The legal limitation that confines liability to harms that are within the foreseeable scope of risk created by the defendant’s breach.

Factual causation is about the actual chain of events; proximate cause is about how far along that chain liability should extend. Both must be satisfied for negligence liability.

Factual Causation: The "But For" Test

Factual causation asks whether the injury would have occurred but for the defendant’s breach. The classic formula is:

• If the harm would not have occurred in the absence of the defendant’s conduct → factual cause is satisfied.
• If the harm would have occurred anyway even without the defendant’s conduct → that conduct is not a but-for cause.

Key Term: But-For Test
A test for factual causation that asks whether the injury would have occurred in the absence of the defendant’s conduct. If not, the conduct is a but-for cause.

The plaintiff bears the burden of proving factual causation by a preponderance of the evidence. Negligence alone is not enough; there must be a causal link between breach and injury.

Importantly, there can be more than one factual cause. Several negligent acts may each be but-for causes of a single harm. On the MBE, do not assume that only one actor can be the cause-in-fact.

Factual causation also matters to defenses. For example, contributory or comparative negligence only reduces (or bars) recovery if the plaintiff’s own negligence was a factual cause of the accident.

Worked Example 1.1

(Original content preserved)

A factory negligently emits toxic fumes. Two nearby residents, A and B, both develop respiratory illness. Medical evidence cannot determine whether A’s illness was caused by the factory or by a different nearby plant, which was also negligent. Both plants are sued.

Answer:
Because both defendants were negligent and it is unclear which caused the harm, the burden shifts to the defendants to prove they did not cause A’s illness. If neither can do so, both may be held jointly liable under alternative liability.

Substantial Factor Test and Multiple Sufficient Causes

The but-for test breaks down when two or more independent acts would each have been sufficient to cause the harm by themselves. In such “multiple sufficient cause” cases, courts use the substantial factor test.

Key Term: Multiple Sufficient Causes
A situation in which two or more independent negligent acts each would have been sufficient on their own to cause the plaintiff’s harm.

Key Term: Substantial Factor Test
A standard used when multiple acts combine to cause harm; each act is a substantial factor if it alone would have been sufficient to produce the result.

Each defendant is a factual cause if their conduct was a substantial factor in bringing about the harm. On the MBE, you’ll see language like:

• “Either collision alone would have totaled the car.”
• “Either fire would have destroyed the house.”

In those situations, neither defendant can escape liability by arguing, “The harm would have occurred anyway because of the other defendant.” Both are causes-in-fact.

Worked Example 1.2

(Original content preserved, slightly expanded)

Two drivers, X and Y, independently drive negligently and each crashes into a parked car at the same time, causing it to be destroyed. Either collision alone would have totaled the car.

Answer:
Both X and Y are liable. This is a multiple sufficient cause case. Each impact by itself would have destroyed the car, so neither defendant can argue the car would have been totaled anyway. Each act was a substantial factor in causing the harm, so both are responsible for the full damage (subject to apportionment between them, but not as against the plaintiff).

Additional Example: Multiple Sufficient Causes and Plaintiff Fault

Consider a variation where the plaintiff is also negligent.

Worked Example 1.3

A motorcyclist’s engine fails on a hilly road at dusk. He leaves the motorcycle in the lane without turning on its hazard lights and goes to seek help. Two drivers, approaching from opposite directions with their headlights off in violation of traffic laws, simultaneously hit the motorcycle. Either impact alone would have totaled the motorcycle.

Answer:
The motorcyclist’s failure to activate hazard lights is negligent, but both drivers are still factual causes under the substantial factor test: each collision alone would have destroyed the motorcycle. Depending on the jurisdiction’s comparative or contributory negligence rules, the motorcyclist’s own negligence may reduce or bar his recovery, but it does not eliminate the drivers’ causal responsibility.

Indeterminate Causes and Alternative Liability

Sometimes it is clear that one of several defendants caused the harm, and all were negligent, but the plaintiff cannot prove which one. Classic examples include multiple hunters negligently firing in the plaintiff’s direction, or several manufacturers selling identical harmful products.

To avoid letting all negligent defendants escape liability merely because the plaintiff cannot identify the specific wrongdoer, courts may apply alternative liability.

Key Term: Alternative Liability
A doctrine that shifts the burden of proof to multiple negligent defendants when it is uncertain which one caused the plaintiff’s harm. Each must prove they did not cause the harm; if they cannot, all may be held liable.

The usual requirements (as tested on the MBE) are:

• All defendants acted tortiously (e.g., all were negligent).
• The harm was caused by one of them (or at most a small, defined group).
• The actual tortfeasor is among the defendants before the court.
• The plaintiff cannot identify which defendant caused the injury.

If these elements are met, the defendants must exculpate themselves. Those who cannot are typically held jointly and severally liable.

Alternative liability is distinct from:

• Market-share liability, which may apportion liability among many manufacturers by market share (rarely tested on the MBE).
• Concert of action, where defendants agree to pursue a common plan and are all liable for resulting harm, even if only one’s act is the immediate cause.

Proximate Cause: Legal Limitation on Liability

Even when factual causation is established, the defendant is only liable for harms that are sufficiently connected to the breach in a legal sense. This is the role of proximate cause.

Key Term: Intervening Cause
An event that occurs after the defendant’s negligent act and contributes to the plaintiff’s harm.

Key Term: Superseding Cause
An intervening event that is so unforeseeable and extraordinary that it breaks the chain of proximate causation, relieving the original defendant of liability for subsequent harm.

Proximate cause focuses on foreseeability:

• Was the type of harm that occurred among the risks that made the defendant’s conduct negligent?
• Was the class of persons harmed (e.g., passengers, pedestrians) reasonably foreseeable?
• Did any intervening acts fall within the scope of the risk created?

If the harm results from a highly unusual, unforeseeable sequence, or if a third party’s act is a superseding cause, the defendant is not liable even though their negligence was a factual cause.

Intervening and Superseding Causes

An intervening cause is any event that occurs after the defendant’s negligence and contributes to the injury. Most intervening causes do not cut off liability; they simply create additional factual causes.

They become superseding causes only when they are:

• Not within the scope of risk created by the defendant’s conduct, and
• So abnormal, extraordinary, or unforeseeable that they break the causal chain.

Common foreseeable intervening events (usually not superseding):

• Ordinary negligence of rescuers (“danger invites rescue”).
• Medical malpractice in treating the original injury.
• Subsequent accidents arising from the weakened condition caused by the initial injury.
• The plaintiff’s reasonable attempts to escape danger.

The original tortfeasor is typically liable for all such foreseeable consequences.

By contrast, the following may be superseding (depending on the facts):

• Intentional criminal acts or intentional torts of third parties that are not reasonably foreseeable.
• Extraordinary forces of nature (e.g., unprecedented earthquake) unrelated to the risk created.

However, if the defendant’s negligence increased the risk of that type of third-party act—such as failing to provide security in a high-crime area, or leaving keys in an unattended vehicle—the criminal act may be treated as a foreseeable intervening cause, not superseding.

Worked Example 1.4

(Original example renumbered for continuity)

A defendant leaves a pit uncovered. Later, a third party pushes the plaintiff into the pit. Is the original defendant liable for the plaintiff’s injuries?

Answer:
If the third party’s act was a foreseeable result of the defendant’s negligence (e.g., the area was known for rough behavior), the defendant remains liable: the pushing is an intervening but not superseding cause. If the act was so unforeseeable and extraordinary that it fell outside the risks created by leaving a pit uncovered, it may be a superseding cause, relieving the defendant of liability.

The "Eggshell Plaintiff" Rule

Defendants take plaintiffs “as they find them.”

Key Term: Eggshell Plaintiff Rule
The principle that a defendant is liable for the full extent of the plaintiff’s injury, even if the injury is more severe than what was foreseeable, due to a pre-existing physical or psychological vulnerability.

Once some physical injury is foreseeable, the defendant is responsible for all resulting harm, even if the plaintiff is unusually fragile (e.g., brittle bones, hemophilia) and suffers catastrophic consequences.

The eggshell plaintiff rule concerns the extent of harm, not the type of harm. The type of harm must still be within the foreseeable scope of risk for proximate cause; but the magnitude, or how badly this particular plaintiff is injured, need not be foreseeable.

The rule applies in negligence, intentional torts, and strict liability.

Multiple Defendants: Joint and Several Liability

When multiple defendants combine to cause an indivisible injury (one that cannot be meaningfully apportioned), each is jointly and severally liable for the entire harm.

Key Term: Joint Tortfeasors
Two or more defendants whose tortious conduct combines to produce a single, indivisible injury to the plaintiff.

Key Term: Joint and Several Liability
The rule that each of multiple defendants responsible for an indivisible harm is liable for the entire amount; the plaintiff may recover all damages from any one of them.

Key points for the MBE:

• The plaintiff can collect the full judgment from any one defendant.
• As between defendants, contribution may redistribute the loss in proportion to fault.
• In some relationships (e.g., employer–employee), the employer may seek indemnity (full reimbursement) from the primary wrongdoer.

Many comparative-fault jurisdictions partially limit joint and several liability (for example, by making it apply only above a certain percentage of fault), but the core MBE principle remains: where an injury is indivisible, each joint tortfeasor is liable to the plaintiff for the full amount.

Joint and several liability frequently interacts with doctrines such as alternative liability, res ipsa loquitur against multiple defendants, and vicarious liability.

Worked Example 1.5

Three drivers, A, B, and C, each drive negligently and collide in an intersection, causing a chain reaction that injures the plaintiff driver. The medical experts testify that the injuries are indivisible—they cannot say what portion was caused by which impact. A, B, and C are all sued.

Answer:
A, B, and C are joint tortfeasors whose negligence combined to cause an indivisible injury. Each is jointly and severally liable to the plaintiff for the full amount of damages. Among themselves, they may seek contribution according to their relative fault, but that does not affect the plaintiff’s ability to recover fully from any one of them.

Rescue Doctrine and Foreseeable Plaintiffs

Proximate cause also determines who is within the class of foreseeable plaintiffs. A key special rule is the rescue doctrine.

Key Term: Rescue Doctrine
The principle that if the defendant’s negligence puts someone in danger, it is foreseeable that a rescuer will attempt to help, and the defendant is liable for injuries suffered by a reasonably conducted rescue.

Rescuers are considered foreseeable plaintiffs. The classic phrase is “danger invites rescue.” A negligent defendant whose conduct creates a dangerous situation is liable not only to the person initially endangered but also to rescuers injured in a reasonable rescue attempt, unless the rescue effort is itself completely reckless.

This doctrine is often tested when a plaintiff is hurt while aiding someone injured by the defendant’s negligence.

Causation and Defenses: Plaintiff Negligence Must Cause the Harm

Contributory or comparative negligence only matters if the plaintiff’s own negligence is a cause-in-fact of the harm. Merely violating a safety statute or acting carelessly is not enough; that breach must also satisfy the but-for (or relevant) test.

For example, a plaintiff’s texting while stopped at a red light may be negligent, but if a speeding driver rear-ends her while she is stationary, her texting is unlikely to be a factual cause of the collision.

This is a favorite MBE trap: a plaintiff may clearly have breached a duty, but if that breach did not contribute causally to the accident, it does not support a contributory or comparative negligence defense.

Loss of Chance (Rare on the MBE)

Some jurisdictions recognize a “loss of chance” doctrine in medical malpractice, where a doctor’s negligence reduces the patient’s chance of survival or recovery. The patient may recover for the lost opportunity even if survival was initially less than 50%.

Key Term: Loss of Chance
A doctrine (not universally adopted) that allows recovery for the reduction in a patient’s probability of recovery or survival caused by medical negligence.

This doctrine is rarely tested on the MBE and should not distract from understanding the core causation rules above.

Worked Example 1.6

A plaintiff is injured in a car crash caused by a defendant’s negligence. While being transported to the hospital, the ambulance is involved in a second accident due to the ambulance driver’s negligence, worsening the plaintiff’s injuries. The defendant argues that the ambulance driver’s negligence is a superseding cause.

Answer:
The defendant remains liable for the additional injuries. The need for medical treatment and the risk of subsequent negligent treatment or accidents during transport are foreseeable consequences of the original negligence. The ambulance driver’s negligence is an intervening, not a superseding, cause, so the original defendant is liable for the full extent of the injuries.

Exam Warning

In MBE questions, do not confuse factual causation with proximate cause. A defendant may be a factual cause but not a proximate cause if the harm is outside the foreseeable scope of risk or results from a superseding event. Conversely, if factual causation is missing, the analysis stops—proximate cause is never reached.

Revision Tip

For each negligence problem, move systematically:

1. Identify any negligent conduct.
2. Ask: Did that conduct satisfy the but-for or substantial factor test?
3. Ask: Is the harm, to this plaintiff, within the foreseeable scope of risk?
4. Check for intervening acts and decide whether they are superseding.
5. Consider whether any joint and several or alternative liability doctrines apply.

Key Point Checklist

This article has covered the following key knowledge points:

• Factual causation is usually established by the but-for test; there may be multiple factual causes.
• The substantial factor test applies when there are multiple sufficient causes, so that simple but-for analysis fails.
• Alternative liability shifts the burden of proof to multiple negligent defendants when the actual cause is indeterminate, provided all likely tortfeasors are before the court.
• Joint and several liability makes each joint tortfeasor liable for the full amount of an indivisible injury, leaving contribution and indemnity issues for defendants.
• Proximate cause limits liability to foreseeable harms to foreseeable plaintiffs, measured by the scope-of-risk approach.
• Intervening causes are common; only unforeseeable, extraordinary intervening events are superseding causes that break the causal chain.
• Subsequent negligence in rescue or medical treatment is usually foreseeable and does not cut off liability.
• The eggshell plaintiff rule makes defendants liable for the full extent of injury, even when the plaintiff’s special vulnerability leads to unexpectedly severe harm.
• Plaintiff negligence affects recovery only if it is itself a factual cause of the harm.
• Rescuers are foreseeable plaintiffs under the rescue doctrine, so the original negligent actor is liable for injuries suffered in a reasonable rescue attempt.

Key Terms and Concepts

• Factual Causation
• But-For Test
• Multiple Sufficient Causes
• Substantial Factor Test
• Alternative Liability
• Joint Tortfeasors
• Joint and Several Liability
• Proximate Cause
• Intervening Cause
• Superseding Cause
• Rescue Doctrine
• Eggshell Plaintiff Rule
• Loss of Chance