Causation: Actual and Proximate Cause

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Causation: Actual and Proximate Cause

Key Takeaways Explain This Topic AI

Actual cause uses the but-for test; where multiple sufficient causes combine, the substantial-factor test applies (Anderson/merged fires), and the burden may shift under alternative-liability (Summers v. Tice) or market-share liability (Sindell).

Proximate cause limits liability to the foreseeable consequences of the defendant's negligence; unforeseeable harms and superseding causes break the causal chain.

Intervening forces that are foreseeable (rescuers, ordinary negligence of others, subsequent medical malpractice, disease, or aggravation) do not cut off liability; unforeseeable, extraordinary intervening forces (superseding causes) do.

The eggshell-plaintiff rule: the defendant takes the plaintiff as found and is liable for the full extent of harm even if its severity was unforeseeable.

California pioneered market-share liability in Sindell v. Abbott Laboratories, apportioning liability among DES manufacturers by market share where the plaintiff cannot identify which made the harmful product.

Last updated: June 2026

Actual (Factual) Cause

Actual cause asks whether the defendant's conduct in fact produced the injury. The default test is the but-for test : but for the defendant's negligence, would the plaintiff have been injured? If the harm would have happened anyway, there is no factual cause.

The but-for test breaks down when multiple sufficient causes converge. If two independently negligent fires merge and burn the plaintiff's home, neither is a but-for cause (each alone would have sufficed), yet both are liable under the substantial-factor test : a defendant whose conduct was a substantial factor in bringing about the harm is a cause in fact ( Anderson v. Minneapolis, St. P. & S. Ste. M. Ry. ).

Where the plaintiff cannot identify which of several negligent defendants caused the harm, two burden-shifting doctrines help:

Alternative liability ( Summers v. Tice ): Two hunters negligently fire in the plaintiff's direction; one pellet strikes him, but he cannot prove whose. The burden shifts to each defendant to prove he was not the cause ; if neither can, both are jointly liable. Requires a small number of defendants, all negligent, all before the court.

Market-share liability ( Sindell v. Abbott Laboratories ): California's landmark doctrine. Where a fungible product (DES, a synthetic estrogen) caused harm years later and the plaintiff cannot identify the specific manufacturer, liability is apportioned among the manufacturers by their share of the relevant market . Each defendant pays its market-share percentage (in California, several liability only — a defendant cannot be made to cover the share of absent manufacturers), and a defendant who proves it could not have made the product the plaintiff used escapes.

Proximate (Legal) Cause and Foreseeability

Even where factual cause is clear, proximate cause limits liability to consequences with a sufficiently close connection to the breach. The unifying principle is foreseeability : a defendant is liable for the foreseeable harmful results of his negligence and not liable for unforeseeable, freakish ones. In re Polemis (direct-cause test) is the historical minority view; the modern rule of Wagon Mound asks whether the type of harm was foreseeable.

Proximate cause analysis turns on intervening forces — events that occur after the defendant's negligence and contribute to the harm. The question is whether the intervening force is foreseeable (does not cut off liability) or unforeseeable and extraordinary (a superseding cause that does).

Foreseeable intervening forces (defendant remains liable):

• Negligent rescue and the efforts of rescuers ('danger invites rescue');
• Subsequent medical malpractice in treating the original injury;
• Subsequent disease or infection arising from the injury;
• Subsequent accident/aggravation caused by the weakened condition;
• Ordinary negligence of third persons that is a normal response to the situation;

Foreseeable reactions (panic, flight) of those endangered.

Superseding causes (defendant relieved): Generally unforeseeable intentional torts and crimes of third parties, extraordinary acts of nature , and grossly abnormal responses. The classic line: ordinary negligence by a later actor is foreseeable and does not supersede; a deliberate, unforeseeable criminal act usually does — unless the defendant's duty was precisely to guard against that criminal act (e.g., a hotel's negligent security).

Palsgraf: the zone-of-danger and Andrews views

Palsgraf v. Long Island R.R. frames the scope of foreseeability at the heart of proximate cause. Cardozo's majority (zone of danger) treats the issue as one of duty : a defendant owes a duty only to plaintiffs within the foreseeable zone of danger , so an unforeseeable plaintiff — like Mrs. Palsgraf, standing far from the dislodged fireworks —

cannot recover at all, because no wrong was done to her . Andrews's dissent (everyone view) treats it as proximate cause : a defendant who is negligent toward anyone owes a duty to the world, and liability turns on a multi-factor proximate-cause inquiry (natural and continuous sequence, directness, foreseeability of harm, remoteness in time and space).

Most courts follow Cardozo, making the foreseeable-plaintiff question a recurring essay issue; California's approach folds foreseeability into both duty ( Rowland v. Christian factors) and proximate cause.

The Eggshell Plaintiff and Putting Causation Together

Once a defendant is liable for some foreseeable harm, the eggshell-plaintiff (thin-skull) rule makes him liable for the full extent of the injury, even if its severity was wildly unforeseeable. 'You take your plaintiff as you find him.' A minor negligent tap that triggers a fatal hemophiliac bleed, or that reactivates a latent disease, yields full liability for the death. Foreseeability governs the type of harm and the existence of duty — not the extent of damages.

A disciplined causation analysis proceeds in this order:

• Step Question Doctrine
• 1 Did the breach in fact cause the harm? But-for; substantial factor; Summers; Sindell
• 2 Was the type of harm foreseeable? Wagon Mound foreseeability
• 3 Did an intervening force contribute? Foreseeable → liable; superseding → relieved
• 4 How much harm is the defendant liable for? Eggshell-plaintiff: full extent

Hypothetical: D negligently rear-ends P, causing a moderate neck injury. The ambulance taking P to the hospital is negligently driven by an EMT and crashes, worsening P's injuries; at the hospital, a surgeon commits malpractice. Is D liable for the aggravated harm? Yes. Negligent ambulance driving and subsequent medical malpractice are foreseeable intervening forces; both are normal incidents of the original injury and do not supersede. D is liable for the entire chain (the EMT and surgeon are also liable as joint tortfeasors).

MBE trap: Students over-apply 'superseding cause' to ordinary third-party negligence. Remember the default: foreseeable negligent intervention is not superseding. Only the extraordinary, unforeseeable, or independent intentional/criminal act (outside the scope of the risk) breaks the chain.