Negligence - But for and substantial causes

Learning Outcomes

This article examines the essential element of causation in Negligence for the MBE. It explains the two required components: actual cause (cause-in-fact) and proximate cause (legal cause). After reading this article, you will be able to distinguish between the 'but-for' test and the substantial factor test for actual cause, apply the concept of foreseeability to determine proximate cause, and identify when intervening forces become superseding causes, enabling you to analyze causation issues in MBE fact patterns effectively.

MBE Syllabus

For the MBE, a thorough understanding of causation in negligence is required. This involves analyzing both factual causation (actual cause) and legal causation (proximate cause). You should be prepared to:

• Apply the 'but-for' test to determine actual cause.
• Recognize situations involving concurrent causes where the 'but-for' test is inadequate.
• Apply the substantial factor test in concurrent cause scenarios.
• Analyze proximate cause based on the foreseeability of the harm and the plaintiff.
• Distinguish between direct and indirect causation.
• Identify intervening forces and determine if they are superseding causes that cut off liability.
• Understand the 'eggshell plaintiff' rule regarding the extent of harm.

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. To establish actual cause in a negligence action, the plaintiff generally must show that the defendant's breach was the:
   1. Sole cause of the injury.
   2. Proximate cause of the injury.
   3. 'But-for' cause of the injury.
   4. Substantial factor in causing the injury.
2. Two motorcyclists simultaneously rev their engines very loudly next to an elderly pedestrian with a known heart condition, causing the pedestrian to suffer a fatal heart attack. Either motorcyclist's noise alone would have been sufficient to cause the heart attack. In a suit against one of the motorcyclists, what test should be used to determine actual cause?
   1. The 'but-for' test.
   2. The foreseeability test.
   3. The substantial factor test.
   4. The risk-utility test.
3. A driver negligently runs a red light, striking a car lawfully proceeding through the intersection. The driver of the struck car is taken to the hospital, where a doctor negligently administers the wrong medication, causing further injury. Is the driver who ran the red light liable for the injuries caused by the doctor's negligence?
   1. Yes, because the driver's negligence was the 'but-for' cause of all subsequent injuries.
   2. Yes, because subsequent medical negligence is generally considered a foreseeable intervening cause.
   3. No, because the doctor's negligence was a superseding cause.
   4. No, unless the driver could specifically foresee the doctor's negligent act.

Introduction

Once duty and breach have been established in a negligence claim, the plaintiff must prove causation. Causation consists of two distinct components, both of which must be proven: actual cause (also known as cause-in-fact or factual cause) and proximate cause (legal cause). Actual cause links the defendant's breach to the plaintiff's injury, asking if the breach actually caused the harm. Proximate cause examines whether the harm was a foreseeable consequence of the breach and whether liability should fairly attach.

Actual Cause (Cause-in-Fact)

The primary test for determining actual cause is the 'but-for' test.

The 'But-For' Test

Under this test, the plaintiff must show that, but for the defendant's negligent act, the injury would not have occurred. If the injury would have happened even without the defendant's negligence, then the defendant's conduct is not the actual cause.

Key Term: Actual Cause The requirement that the defendant's negligent conduct was a necessary antecedent to the plaintiff's injury; the injury would not have occurred 'but for' the defendant's act, or the act was a substantial factor in causing the injury.

Worked Example 1.1

Driver negligently fails to stop at a stop sign and enters an intersection. Pedestrian, who was properly crossing the street, is struck and injured by Driver's car. Would Pedestrian have been injured if Driver had stopped at the sign?

Answer: No. But for Driver's negligent failure to stop, Pedestrian would not have been injured. Driver's negligence is the actual cause of Pedestrian's injury.

Problems with the 'But-For' Test: Concurrent Causes

The 'but-for' test proves inadequate in situations involving multiple negligent acts, any one of which would have been sufficient alone to cause the injury. These are often called concurrent cause situations.

• Multiple Sufficient Causes: Where two or more defendants (or a defendant and a natural force) commit separate negligent acts, each of which alone would have been sufficient to cause the plaintiff's injury, the 'but-for' test fails. Applying it to either defendant individually suggests that the injury would have occurred even without that specific defendant's negligence (because the other defendant's act would still have caused it).

The Substantial Factor Test

To address the multiple sufficient causes problem, courts use the substantial factor test. Under this test, if a defendant's negligent act was a substantial factor in bringing about the plaintiff's injury, the defendant is an actual cause (even if not the 'but-for' cause). An act is a substantial factor if it contributed materially to the harm. This test is typically applied when multiple forces combine simultaneously to cause the harm.

Key Term: Substantial Factor Test An alternative to the 'but-for' test used in concurrent cause situations; asks whether the defendant's conduct was a substantial factor in bringing about the plaintiff's harm.

Worked Example 1.2

Two campers in different parts of a forest negligently fail to extinguish their campfires. Each fire spreads independently. The two fires merge and burn down Plaintiff's cabin. Expert testimony establishes that either fire alone would have been sufficient to destroy the cabin. Plaintiff sues one of the campers. Is that camper's negligence an actual cause?

Answer: Yes. Although the 'but-for' test fails (the cabin would have burned down anyway due to the other fire), the camper's negligence was a substantial factor in causing the destruction. Under the substantial factor test, the camper is an actual cause.

Proximate Cause (Legal Cause)

Even if the defendant's conduct is the actual cause of the plaintiff's harm, liability will attach only if the conduct is also the proximate cause. Proximate cause is a legal limitation on liability, essentially asking whether the harm was a foreseeable result of the defendant's negligence.

Key Term: Proximate Cause The legal requirement that the plaintiff's injury must have been a foreseeable result of the defendant's negligent conduct, and that no superseding intervening cause broke the chain of causation.

Foreseeability Test

The dominant test for proximate cause is foreseeability. Was the type of harm suffered by the plaintiff a foreseeable result of the defendant's negligent conduct? If the harm was foreseeable, the defendant's conduct is the proximate cause.

• Unforeseeable Type of Harm: If the type of harm that occurred was not foreseeable, the defendant is generally not liable, even if their negligence was the actual cause.
• Extent of Harm (Eggshell Plaintiff Rule): The extent of the harm need not be foreseeable. The defendant takes the plaintiff as they find them. If the defendant's negligence causes foreseeable harm (e.g., a minor impact), but the plaintiff suffers unusually severe injuries due to a pre-existing vulnerability (the "eggshell skull"), the defendant is liable for the full extent of the injuries.
• Foreseeable Plaintiff: The harm must be foreseeable to a plaintiff within the "zone of danger." Liability generally does not extend to unforeseeable plaintiffs.

Direct vs. Indirect Causation: Intervening Forces

• Direct Cause: If the harm results directly from the defendant's negligence without any external intervening force, proximate cause is usually established if the harm was foreseeable.

• Indirect Cause (Intervening Forces): Often, an intervening force comes into play after the defendant's negligent act and combines with it to cause the injury. The key question is whether the intervening force was foreseeable.

  • Foreseeable Intervening Forces: If the intervening force was a normal or foreseeable consequence of the situation created by the defendant's negligence, it does not cut off liability. The defendant remains the proximate cause. Common foreseeable intervening forces include:
    • Subsequent medical malpractice (negligent treatment of injuries caused by defendant).
    • Negligence of rescuers ("danger invites rescue").
    • Normal responses or reactions to the defendant's act (e.g., fleeing from danger).
    • Subsequent diseases or accidents caused by the weakened condition resulting from the original injury.
  • Unforeseeable Intervening Forces (Superseding Causes): If the intervening force was unforeseeable and produced an unforeseeable result, it is generally deemed a superseding cause. A superseding cause breaks the chain of proximate causation, relieving the defendant of liability for the harm caused by the superseding force. Unforeseeable criminal acts or intentional torts of third parties are often superseding causes, unless the defendant's negligence created a foreseeable risk of such conduct (e.g., leaving keys in a car in a high-crime area).

Key Term: Intervening Cause A force that comes into play after the defendant's negligent act and combines with it to cause the plaintiff's injury.

Key Term: Superseding Cause An unforeseeable, intervening cause that breaks the chain of proximate causation between the defendant's initial negligent act and the plaintiff's ultimate injury, relieving the defendant of liability for that injury.

Worked Example 1.3

Driver negligently speeds through a residential area, loses control, and crashes into a utility pole, knocking it down. The impact causes sparks that ignite dry leaves nearby, starting a small fire. An arsonist, unrelated to the driver, sees the small fire and decides to add gasoline, causing the fire to spread rapidly and burn down Plaintiff's house. Is Driver's negligence the proximate cause of the destruction of Plaintiff's house?

Answer: Likely no. While Driver's negligence was the actual cause ('but-for' the crash, the pole wouldn't have fallen, no sparks, no initial fire), the arsonist's act of intentionally adding gasoline and greatly expanding the fire was likely an unforeseeable criminal act of a third party. This act would be considered a superseding cause, breaking the chain of proximate causation from Driver's initial negligence to the destruction of the house.

Exam Warning

Do not confuse actual cause ('but-for' or substantial factor) with proximate cause (foreseeability). Both must be proven for negligence liability. An act can be the actual cause but not the proximate cause if the resulting harm or the manner in which it occurred was unforeseeable.

Key Point Checklist

This article has covered the following key knowledge points:

• Causation in negligence requires proof of both actual cause and proximate cause.
• The primary test for actual cause is the 'but-for' test.
• The substantial factor test applies to concurrent causes where the 'but-for' test fails.
• Proximate cause is primarily based on the foreseeability of the type of harm.
• The extent of harm need not be foreseeable (eggshell plaintiff rule).
• Liability requires a foreseeable plaintiff within the zone of danger.
• Foreseeable intervening forces do not break the chain of proximate causation.
• Unforeseeable intervening forces, especially criminal acts or intentional torts, may be superseding causes that cut off liability.

Key Terms and Concepts

• Actual Cause
• Substantial Factor Test
• Proximate Cause
• Intervening Cause
• Superseding Cause