What You'll Learn

  • The but-for test 2. Proof and inference
  • Multiple sufficient causes 4. Burden-shifting doctrines
  • An actual-cause sequence

Educational information only; not legal advice. This article is a general study aid and should be checked against current authority and course materials.

1. Prove More Than Sequence

Direct proof Evidence identifies the physical chain between conduct and injury, such as a collision, toxic exposure, or failed medical treatment. Circumstantial proof Facts may support a reasonable inference of causation even when no witness saw the entire sequence.

Probability The plaintiff ordinarily must show that causation is more likely than not, not merely possible. Post hoc fallacy The fact that harm occurred after negligence does not by itself prove that negligence caused the harm.

Where expert testimony presents only a possibility, causation may fail. The plaintiff must connect the breach to the injury with evidence sufficient for a reasonable factfinder to conclude that causation is probable.

2. Use the Doctrine That Matches the Causal Structure

Multiple-cause problems are not all the same. First ask whether each force was necessary, whether each was independently sufficient, or whether the wrongdoer cannot be identified.

Problem Causal structure Doctrine or effect

Concurrent causes Separate acts combine to produce one harm; each contributes to the result. Each contributing act can be a factual cause; indivisible harm may support shared liability.

Multiple sufficient causes Each independent force would have been enough to cause the harm by itself. Traditional but-for logic is relaxed so each sufficient force may count as a cause.

Successive causes Events occur at different times and may aggravate or create distinct injuries. Apportion if possible; each actor is responsible for the harm caused.

Alternative liability All defendants were negligent, one caused the harm, but the plaintiff cannot identify which one. Burden shifts to the defendants to absolve themselves or apportion responsibility.

Market-share liability A fungible product caused harm, but the manufacturer cannot be identified. Some courts assign liability in proportion to market share.

Loss of chance Medical negligence reduces the probability of survival or recovery. Some jurisdictions permit proportional recovery; the outlines note that jurisdictions differ.

Key Takeaway

Use ordinary but-for analysis whenever it can sensibly answer the question. The outlines caution against an open-ended "substantial factor" label that can distract from whether the conduct actually made a causal difference.

Alternative liability is narrow

The defendants generally must all have acted tortiously toward the plaintiff, and the circumstances must make one of them the actual wrongdoer. The doctrine does not replace proof whenever causation is simply uncertain.

Market share and loss of chance vary by jurisdiction

State the jurisdictional rule supplied by the course or question. Do not assume that every court recognizes these exceptions.

3. Write Actual Cause Precisely

1 Identify the exact breach and the exact injury for which causation must be proved. 2 Apply the but-for test first unless the causal structure makes it impossible. 3 Explain why the evidence supports probability rather than mere possibility. 4 Classify the problem as concurrent, multiple-sufficient, successive, alternative, or market-share causation. 5 If a burden shifts, explain what triggered the shift and what each defendant must show. 6 Keep actual cause separate from proximate cause; factual connection does not decide the legal scope of liability.

Key Takeaway

Two hunters negligently fire in the plaintiff's direction at the same moment. One pellet causes the injury, but the evidence cannot identify which gun fired it. If both hunters are before the court and both acted negligently, alternative liability may shift the burden to each hunter to show that the other caused the harm.

Common Mistake

Do not use "substantial factor" as a substitute for analysis. Describe why the conduct was necessary, independently sufficient, or part of a doctrine that justifies shifting the burden.

Primary Authorities

  • • Perkins v. Texas & New Orleans Railroad Co. (negligence must make a causal difference).

  • • Kramer Service, Inc. v. Wilkins (possibility and sequence are insufficient).

  • • Anderson v. Minneapolis, St. P. & S. St. M. Ry. Co. (independent sufficient fires).

  • • Summers v. Tice (alternative liability).

  • • Sindell v. Abbott Laboratories (market-share liability).

  • • Doull v. Foster (but-for analysis in a multiple-cause medical case).

Exam-ready conclusion

Actual cause is factual linkage. Begin with but-for causation, identify the causal structure, and use burden-shifting or multiple-cause doctrines only when ordinary proof cannot fairly resolve the problem.