Negligence - Superseding causes

Learning Outcomes

This article explains superseding causes in negligence for MBE-style proximate cause questions, including:

• How to distinguish intervening causes from superseding causes by focusing on foreseeability, scope of risk, and whether the later act is responsive or independent.
• How to apply the scope-of-risk and foreseeability tests step-by-step to later events in a causal chain, and articulate why a particular harm is or is not within the defendant’s scope of liability.
• How to analyze the effect of criminal acts, intentional torts, negligent third parties, and natural forces (acts of God) on the original defendant’s liability, and when those forces are treated as superseding.
• How to handle responsive intervening forces such as rescue attempts, escape efforts, medical treatment, subsequent diseases, and later accidents in a weakened condition, and explain why they usually do not cut off liability.
• How to evaluate questions involving concurrent tortfeasors, subsequent medical malpractice, and the eggshell plaintiff rule, and determine the full extent of damages attributable to the original defendant.
• How to structure an exam answer on proximate cause: separating factual cause from legal cause, spotting possible intervening acts, and arguing both sides on whether the chain of causation is broken.

MBE Syllabus

For the MBE, you are required to understand how intervening acts affect a defendant’s liability in negligence, with a focus on the following syllabus points:

• The definition and role of superseding causes in negligence
• The difference between intervening and superseding causes
• The foreseeability test for intervening events and the scope-of-risk approach
• The effect of criminal acts, intentional torts, and acts of God on proximate cause
• The impact of rescuers, medical malpractice, subsequent accidents, and diseases
• How to determine when a defendant is relieved from liability due to a superseding cause

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 of the following is most likely to be considered a superseding cause that relieves a defendant of liability?
   1. A foreseeable act of negligence by a third party.
   2. An unforeseeable criminal act by a third party.
   3. A foreseeable reaction by the plaintiff to the defendant’s conduct.
   4. A subsequent medical error that aggravates the plaintiff’s injury.
2. If an intervening act is deemed foreseeable, what is the effect on the original defendant’s liability?
   1. The defendant is always relieved of liability.
   2. The defendant remains liable for the harm.
   3. The intervening act is always a superseding cause.
   4. The plaintiff cannot recover from anyone.
3. Which of the following is NOT typically a superseding cause?
   1. Grossly negligent medical treatment.
   2. Ordinary negligence by a rescuer.
   3. A natural event that was foreseeable.
   4. A subsequent disease resulting from the original injury.

Introduction

In negligence, a defendant is liable only for harm that is proximately caused by their conduct. Sometimes, after the defendant’s act, another event or act occurs and contributes to the plaintiff’s injury. Whether the defendant remains liable depends on whether this later event is a mere intervening cause or a superseding cause that breaks the chain of causation.

Key Term: Proximate Cause
The legal limitation on actual (factual) causation that restricts a defendant’s liability to harms that bear a sufficiently close relationship to the defendant’s negligent conduct, usually framed in terms of foreseeability or scope of risk.

Modern courts often express proximate cause using the scope-of-risk or scope of liability approach.

Key Term: Scope of Liability
The set of harms that fall within the risks that made the defendant’s conduct negligent in the first place. A defendant is liable only for those harms that materialize from the very dangers that rendered the conduct unreasonable.

So proximate cause asks: Did the plaintiff suffer the type of harm that made the defendant’s conduct negligent to begin with? Superseding-cause analysis is simply a more specific version of this inquiry applied to later events.

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

Key Term: Superseding Cause
An intervening act or event that is so unforeseeable and independent, and so outside the scope of the risks created by the defendant, that it breaks the chain of proximate causation, relieving the original defendant of liability.

Intervening vs. Superseding Causes

An intervening cause is any later event that joins with the defendant’s conduct to produce the injury. Not all intervening causes relieve the defendant of liability. Only those classified as superseding will cut off the defendant’s responsibility.

Historically, courts drew a sharp line:

• Intervening cause → does not break the chain
• Superseding cause → does break the chain

Today, many courts emphasize the scope-of-risk analysis rather than labels. The central question is:

• Was the injury that actually occurred one of the risks that made the defendant’s conduct negligent, or did it result from an entirely different, unforeseeable risk created by someone else or by nature?

If the later event and resulting harm fall within the risks that made the defendant’s conduct unreasonable, the event is merely intervening and not superseding.

Illustrations of the scope-of-risk idea:

• A trolley operator speeds through a neighborhood. A tree, loosened by an unrelated storm, suddenly falls onto the trolley and injures passengers. Speeding increases the risk of traffic collisions, not random falling trees. Being hit by a tree may be outside the scope of risks that make speeding negligent; the tree fall may be a superseding cause.
• An adult negligently gives a handgun to a child. The child drops the gun on his own foot and is injured. The risk that makes this conduct negligent is that the child might fire the gun and shoot someone, not that he might be injured by its weight. The dropped-gun injury may fall outside the scope of liability.
• A contractor negligently fails to barricade an open shaft at a construction site. The obvious risk is that someone will fall in. Instead, a radiator is accidentally pushed into the shaft and injures a worker below. A court might find that the failure to barricade the shaft created a general risk of falling objects injuring someone below, so the harm is within the scope of liability.

Exam questions may still use the terminology of “intervening” versus “superseding,” but the core reasoning is foreseeability of the type of harm and scope of risk.

The Foreseeability Test

Foreseeability is the central tool for deciding whether an intervening act is superseding.

Key Term: Foreseeability
The likelihood that a reasonable person in the defendant’s position would have anticipated the intervening act or resulting harm as a possible consequence of their conduct.

If the intervening event was a normal or foreseeable response to the defendant’s negligence, it will not be a superseding cause. The defendant remains liable.

If the intervening act is extraordinary, highly unusual, or not reasonably anticipated, and produces a type of harm outside the risks that made the defendant negligent, it is likely a superseding cause, and the defendant is not liable for the later harm.

Courts sometimes describe four patterns combining foreseeability of result and intervening force:

• Foreseeable result + foreseeable intervening force → Defendant liable.
• Foreseeable result + unforeseeable intervening force → Defendant usually liable (except when the intervening force is an unforeseeable crime or intentional tort).
• Unforeseeable result + foreseeable intervening force → Defendant usually not liable.
• Unforeseeable result + unforeseeable intervening force → Intervening force is superseding; defendant not liable.

Importantly, proximate cause focuses on the type of harm, not its precise extent or manner.

Key Term: Eggshell Plaintiff Rule
Once the type of harm is foreseeable, the defendant is liable for the full extent of that harm, even if the plaintiff is unusually vulnerable and suffers more severe injuries than an ordinary person would.

So, if a car crash foreseeably causes minor physical injuries, the defendant is also liable if the plaintiff’s rare bone condition turns that impact into a catastrophic injury. The severity is not a superseding cause.

Types of Intervening Events

Some intervening acts are almost always considered foreseeable and thus not superseding. Others are more likely to be superseding. It helps to distinguish two broad categories.

Key Term: Responsive Intervening Force
An intervening act that is a direct reaction or response to the danger created by the defendant’s negligence (e.g., rescue attempts, efforts to escape danger, medical treatment).

Key Term: Independent Intervening Force
An intervening act or event that operates on the situation created by the defendant’s negligence but arises from independent sources (e.g., separate negligent actors, criminal acts, certain natural events).

Responsive (Dependent) Intervening Acts — Usually Not Superseding

These are typical responses to the dangerous situation created by the defendant. They are usually considered foreseeable:

• Ordinary negligence by rescuers or third parties
• Efforts to protect persons or property endangered by the defendant’s conduct
• Reasonable attempts by the plaintiff to escape or to mitigate harm
• Subsequent medical treatment (even if negligent)
• Subsequent diseases or physical conditions resulting from the weakened state caused by the original injury
• Subsequent accidents where the original injury is a substantial factor (e.g., a plaintiff on crutches falls and suffers further injury)

Because these are ordinary reactions to danger, they almost never break the chain.

Example (subsequent accident):
A driver negligently breaks the plaintiff’s leg. Later, while walking carefully on crutches, the plaintiff slips on a negligently maintained supermarket floor and breaks her arm. The original driver is still liable for the arm injury: needing crutches was a foreseeable consequence of the first injury, and being less stable on crutches makes a fall foreseeable. The supermarket is also liable as a concurrent tortfeasor.

Key Term: Concurrent Tortfeasor
A second tortfeasor whose conduct combines with the defendant’s negligence to cause the plaintiff’s harm. Each is liable for the full extent of the indivisible injury.

Independent Intervening Acts — Sometimes Superseding

Independent intervening forces are more likely to be superseding, especially if they involve criminal acts or extraordinary natural events. Common categories include:

• Negligent acts of third persons
• Criminal acts or intentional torts of third persons
• Acts of God and unusual natural forces

However, even these may be foreseeable if the defendant’s negligence increased the risk that such forces would cause harm.

Criminal Acts and Intentional Torts

If a third party’s criminal act or intentional tort is not foreseeable, it is usually a superseding cause. Courts are reluctant to hold a negligent actor responsible for a completely unexpected deliberate wrongdoer.

Key Term: Acts of God
Natural events (such as storms, floods, earthquakes, or lightning) that occur without human agency. They are superseding causes only when they are extraordinary and not reasonably foreseeable in light of the circumstances.

But criminal acts and intentional torts are not automatically superseding. If the defendant’s conduct created or increased a foreseeable risk of such acts, the criminal conduct may be treated as foreseeable and merely intervening, so the defendant remains liable.

Situations where third-party crime is often foreseeable:

• A business or landlord knows the premises are in a high-crime area and negligently fails to take basic security measures.
• A common carrier or innkeeper fails to protect passengers or guests from reasonably foreseeable assaults.
• A parking lot attendant leaves keys in a car in circumstances where theft is likely.
• A contractor leaves a ladder or other access tool at an unoccupied building, making break-ins foreseeable.

In these settings, the defendant’s negligence creates the very risk of criminal activity that later materializes.

Acts of God and Natural Events

Natural events, such as storms or earthquakes, are superseding causes only if they are so unusual that no reasonable person could have anticipated them in light of the defendant’s conduct.

• If a roofer leaves tools unsecured on a roof, and a typical strong wind blows a hammer off the roof onto a passerby, the wind is foreseeable. The roofer’s negligence includes the risk that wind will dislodge tools; the wind is not a superseding cause.
• If a defendant complies with all ordinary precautions, and a historically unprecedented tsunami destroys the property, that event may be a superseding cause because it was outside any reasonable set of risks the defendant’s conduct created.

Medical Malpractice and Subsequent Harm

Subsequent medical treatment is typically foreseeable. Injured plaintiffs commonly seek medical care, and ordinary medical errors are part of that risk. Therefore:

• Ordinary medical negligence does not break the chain of causation.
• The original tortfeasor is liable for the aggravation of the injury caused by negligent treatment, in addition to the original harm.
• Only grossly negligent or intentional misconduct by medical providers might be treated as superseding in some jurisdictions, and even then, exam questions usually signal this with extreme facts.

Worked Example 1.1

A driver negligently leaves a car blocking a lane on a busy street. Later, a thief steals the car and, while fleeing, hits a pedestrian. Is the driver liable for the pedestrian’s injuries?

Answer:
The key question is whether theft of the car and a resulting collision are within the foreseeable risks created by the driver’s negligence. If car thefts are common in the area and the driver’s conduct made theft likely (for example, leaving the keys in the ignition in a high-crime neighborhood), then theft and dangerous driving by the thief may be foreseeable. In that case, the theft is an intervening but not superseding cause, and the driver remains liable as a proximate cause. If, by contrast, car thefts are rare, the neighborhood is very safe, and nothing about the situation made theft likely, the thief’s conduct may be an unforeseeable criminal act and a superseding cause, relieving the driver of liability for the pedestrian’s injuries.

Worked Example 1.2

A store owner negligently fails to repair a broken step. A customer trips, falls, and is taken to the hospital. The doctor commits an ordinary error in treatment, worsening the injury. Is the store owner liable for the aggravated harm?

Answer:
Yes. Seeking medical treatment is a normal response to injury, and some degree of medical negligence is foreseeable. The doctor’s mistake is a responsive intervening force, not a superseding cause. The store owner remains liable for the full extent of the injuries, including the aggravation caused by the negligent treatment. The doctor is also liable as a concurrent tortfeasor.

Worked Example 1.3

A landlord negligently fails to fix a broken lock. A burglar enters and assaults a tenant. Is the landlord liable for the tenant’s injuries?

Answer:
The analysis focuses on foreseeability of criminal activity in light of the landlord’s negligence. If the building is in an area with known break-ins or prior assaults and the defective lock creates an obvious security risk, the assault may be a foreseeable result of failing to maintain the lock. The burglar’s act is then an intervening but not superseding cause, and the landlord may be liable. If, however, the area has virtually no history of crime and there is no reason to anticipate such an assault, the burglar’s intentional attack may be an unforeseeable criminal act and a superseding cause, cutting off the landlord’s liability.

Worked Example 1.4

A construction company negligently leaves a deep trench unguarded next to a sidewalk. A pedestrian steps into the trench to retrieve a dropped item and is injured. While helping the pedestrian out, a passerby negligently drops a tool, causing additional injury to the pedestrian. Is the construction company liable for the second injury?

Answer:
Yes. The passerby’s negligent conduct is a foreseeable response to the hazardous condition created by the construction company. It is foreseeable both that someone might fall into the trench and that others will attempt a rescue, perhaps negligently. The passerby’s negligence is an intervening but not superseding cause. The construction company remains liable for both injuries, along with the passerby as a concurrent tortfeasor.

Worked Example 1.5

A railroad negligently carries a passenger past his stop and forces him to disembark late at night in a notoriously high-crime neighborhood. While walking home, he is assaulted. Is the railroad liable for his injuries?

Answer:
Likely yes. The railroad’s negligence placed the passenger in a foreseeable zone of criminal danger by forcing him to disembark in a high-crime area. The risk that someone in that situation will be assaulted is precisely the kind of harm that makes the railroad’s conduct negligent. The assailant’s criminal act is therefore an intervening but not superseding cause. The railroad may be held liable for the assault injuries.

Worked Example 1.6

A driver speeds through a residential neighborhood, causing a pedestrian to jump back onto the sidewalk to avoid being hit. While waiting on the sidewalk, the pedestrian is mugged by a stranger. Is the driver liable for the mugging?

Answer:
No. Although the driver’s speeding was negligent and a factual cause of the pedestrian’s presence at the later time and place, the risk that someone will be mugged simply because a car sped by is not one of the risks that makes speeding negligent. The mugging is an independent, unforeseeable criminal act and a superseding cause, breaking the chain of proximate causation. The driver is not liable for the mugging injuries.

Worked Example 1.7

A motorist negligently hits a cyclist, breaking the cyclist’s leg. While recovering and walking with crutches, the cyclist trips over a small crack in the sidewalk and injures her wrist. Is the motorist liable for the wrist injury?

Answer:
Yes. The original injury made it foreseeable that the cyclist would be temporarily unstable and at greater risk of falling. The subsequent fall is a foreseeable result of the weakened condition caused by the initial negligence, even though the specific crack was not foreseeable. The motorist remains liable for both the leg and wrist injuries; the sidewalk defect may also subject the property owner to liability.

Exam Warning

In MBE questions, do not assume every criminal act or act of God is a superseding cause. Always analyze whether the event and resulting harm were within the foreseeable risks created by the defendant’s conduct and whether the defendant’s negligence increased the likelihood of that kind of event.

Revision Tip

When analyzing proximate cause, ask two questions:

• Was the intervening act a normal or foreseeable result or response to the defendant’s negligence?
• Is the type of harm that occurred one of the risks that made the defendant’s conduct negligent?
  If both answers are yes, the defendant usually remains liable.

Key Point Checklist

This article has covered the following key knowledge points:

• A superseding cause is an unforeseeable, independent intervening act that breaks the chain of proximate causation by producing a harm outside the risks that made the defendant’s conduct negligent.
• Foreseeable intervening acts, especially responsive acts like rescue, escape, medical treatment, and subsequent accidents in a weakened condition, do not relieve the defendant of liability.
• Criminal acts and intentional torts by third parties are superseding causes only when they are unforeseeable in light of the risks created by the defendant; they are not superseding when the defendant’s negligence makes such acts likely.
• Acts of God (natural events) cut off liability only when they are extraordinary and not reasonably foreseeable, given the situation the defendant created.
• Ordinary negligence by rescuers or medical providers is usually foreseeable and not superseding; the original tortfeasor remains liable for any aggravation of injuries.
• The scope-of-risk approach focuses on whether the type of harm falls within the set of dangers that made the defendant’s conduct negligent, not on the precise details of how the harm occurred.
• The eggshell plaintiff rule means that once the type of harm is foreseeable, the defendant is liable for the full extent of that harm, even if the plaintiff’s particular injuries are more severe than expected.
• Exam analysis should separate actual cause from proximate cause, then systematically assess whether any later events qualify as superseding causes that break the chain of liability.

Key Terms and Concepts

• Proximate Cause
• Scope of Liability
• Intervening Cause
• Superseding Cause
• Foreseeability
• Responsive Intervening Force
• Independent Intervening Force
• Acts of God
• Eggshell Plaintiff Rule
• Concurrent Tortfeasor