Learning Outcomes
After reading this article, you will be able to identify and apply the rules for negligence where harm may be caused by multiple actors or events. You will understand the difference between concurrent and alternative causes, the substantial factor test, and how liability is allocated when more than one defendant may have caused the plaintiff’s injury. You will be able to answer MBE-style questions on these issues.
MBE Syllabus
For MBE, you are required to understand how negligence law addresses situations where harm may be attributable to more than one cause or party. This includes:
- Recognizing when the "but for" test is inadequate due to multiple sufficient causes.
- Applying the substantial factor test for concurrent causation.
- Understanding alternative liability and burden-shifting when the actual cause is uncertain.
- Knowing how liability is apportioned among multiple defendants.
- Identifying when joint and several liability applies.
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.
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When two defendants act independently, and either act alone would have been sufficient to cause the plaintiff’s harm, which test is used to determine actual causation?
- But-for test
- Substantial factor test
- Proximate cause test
- Market share liability
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If two hunters negligently fire in the plaintiff’s direction, but only one bullet causes injury and it is impossible to tell whose shot hit the plaintiff, what doctrine may apply?
- Res ipsa loquitur
- Alternative liability
- Comparative negligence
- Last clear chance
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In a negligence case with multiple defendants, when is joint and several liability most likely to apply?
- When each defendant’s act is a but-for cause of harm
- When the harm is indivisible and caused by concurrent acts
- When the plaintiff is contributorily negligent
- When the harm is divisible
Introduction
Negligence cases often involve situations where more than one act or event could have caused the plaintiff’s injury. The law must determine when each defendant is liable, how causation is established, and how damages are apportioned. This article explains the rules for harms traceable to multiple causes, focusing on concurrent and alternative causation, the substantial factor test, and burden-shifting doctrines.
Multiple Causes in Negligence
Negligence law recognizes that harm may result from the actions of more than one party, or from several independent events. The standard "but for" test for actual causation may not always be adequate in these cases.
Key Term: Concurrent Causes Two or more acts or events that operate simultaneously or together to produce an indivisible injury, where either act alone would have been sufficient to cause the harm.
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 indivisible injury.
The Substantial Factor Test
When two or more defendants act independently, and each act alone would have been sufficient to cause the plaintiff’s harm, the "but for" test fails because neither act is strictly necessary for the injury. In these cases, courts use the substantial factor test.
Key Term: Substantial Factor Test A causation test used when multiple independent acts could each have caused the harm; a defendant is liable if their conduct was a substantial factor in bringing about the injury.
Application
If both defendants’ acts were substantial factors in causing the harm, each is liable. This often results in joint and several liability, meaning the plaintiff can recover the full amount from any liable defendant.
Alternative Liability and Burden Shifting
Sometimes, multiple defendants are negligent, but only one actually caused the harm, and it is impossible for the plaintiff to prove which one. In these cases, courts may shift the burden of proof to the defendants.
Requirements
- All defendants must have acted negligently.
- The injury was caused by one of the defendants.
- The actual cause cannot be determined by the plaintiff.
- All possible tortfeasors are before the court.
If these are met, each defendant must show they did not cause the harm. If neither can do so, both may be held liable.
Joint and Several Liability
When harm is indivisible and caused by multiple concurrent acts, each defendant whose conduct was a substantial factor may be held jointly and severally liable. The plaintiff may recover the full amount from any one defendant, who can then seek contribution from others.
Key Term: Joint and Several Liability A rule under which each of multiple defendants is liable for the entire harm when their concurrent acts produce an indivisible injury.
Apportionment of Damages
If the harm is divisible (e.g., separate injuries), each defendant is liable only for the portion they caused. If the harm is indivisible, joint and several liability applies.
Worked Example 1.1
Two factories, A and B, independently discharge pollutants into a river. Either discharge alone would have been sufficient to kill the fish population. The plaintiff sues both for damages to his fishing business. What test applies, and who is liable?
Answer: The substantial factor test applies. Since each discharge was sufficient to cause the harm, and both were substantial factors, both A and B are liable for the entire harm under joint and several liability.
Worked Example 1.2
Three companies manufacture a drug. The plaintiff develops an illness after taking the drug but cannot prove which company’s product she used. All companies used the same formula and were negligent in failing to warn of risks. What doctrine may apply?
Answer: The doctrine of alternative liability may apply. If all possible tortfeasors are before the court, the burden shifts to each company to prove it did not cause the harm. If none can do so, all may be held liable.
Worked Example 1.3
Two drivers, D1 and D2, negligently collide, causing a fire that spreads and destroys P’s house. It is impossible to determine whether D1 or D2’s car started the fire, but both were negligent. What result?
Answer: If both acts were substantial factors and the harm is indivisible, both D1 and D2 are jointly and severally liable for the entire loss.
Exam Warning
On the MBE, if you see a fact pattern where either defendant’s act alone would have caused the harm, do not use the "but for" test. Apply the substantial factor test and consider joint and several liability.
Revision Tip
If the plaintiff cannot prove which of several negligent defendants caused the harm, look for facts supporting alternative liability and burden shifting.
Key Point Checklist
This article has covered the following key knowledge points:
- The "but for" test is inadequate when multiple sufficient causes exist.
- The substantial factor test is used for concurrent causes where either act alone would have caused the harm.
- Alternative liability shifts the burden to defendants when the actual cause is uncertain and all are negligent.
- Joint and several liability applies when harm is indivisible and caused by concurrent acts.
- Damages are apportioned only if harm is divisible; otherwise, each defendant may be liable for the whole.
Key Terms and Concepts
- Concurrent Causes
- Alternative Liability
- Substantial Factor Test
- Joint and Several Liability
