Causation in Tort Law
Causation in tort law requires proving both actual cause (but-for or substantial factor) and proximate cause (foreseeability), connecting the defendant's conduct to the plaintiff's harm.
Overview
Causation is the critical link between the defendant's breach of duty and the plaintiff's injury. Tort law requires two types of causation: actual cause (cause-in-fact) and proximate cause (legal cause).
Actual cause is typically established through the but-for test: but for the defendant's negligent act, would the plaintiff have been injured? When multiple defendants contribute to a single indivisible injury, courts may use the substantial factor test — asking whether each defendant's conduct was a substantial factor in causing the harm, even if neither alone would have been sufficient.
Special causation problems arise with multiple tortfeasors. In Summers v. Tice, where two hunters simultaneously fired and one pellet struck the plaintiff, the court shifted the burden of proof to the defendants to show which one caused the injury. In Sindell v. Abbott Laboratories, the court adopted market share liability for DES manufacturers, allocating liability based on each manufacturer's share of the market.
Proximate cause limits the scope of liability by requiring that the harm be a foreseeable consequence of the defendant's conduct. The Palsgraf debate frames the key question: does foreseeability limit duty (Cardozo) or proximate cause (Andrews)? Intervening causes — particularly superseding causes that are unforeseeable — may break the causal chain and relieve the defendant of liability.
Key Takeaway
Causation requires two showings: actual cause (the defendant's conduct was a factual cause of harm) and proximate cause (the harm was within the scope of foreseeable risk).
Exam Tip
When you see multiple defendants or unusual causal chains, consider alternative causation theories: substantial factor, alternative liability (Summers v. Tice), market share liability (Sindell), and loss of chance. Always analyze intervening and superseding causes separately.
Landmark Cases (8)
Frequently Asked Questions
What is the but-for test for causation?
The but-for test asks: would the plaintiff's injury have occurred but for the defendant's negligent conduct? If the injury would have happened anyway, the defendant's conduct is not the actual cause.
When is the substantial factor test used instead of but-for?
The substantial factor test is used when multiple causes each independently could have caused the harm (concurrent causes), making the but-for test inadequate. Each defendant's conduct need only be a substantial factor in causing the injury.
What is a superseding cause?
A superseding cause is an unforeseeable intervening event that breaks the chain of proximate causation, relieving the original defendant of liability. Foreseeable intervening causes generally do not break the chain.
What is market share liability?
Market share liability, from Sindell v. Abbott Laboratories, allocates liability among multiple manufacturers based on their market share when the plaintiff cannot identify which specific manufacturer caused the harm. It applies in limited circumstances, primarily involving fungible products.
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