16.2 Proximate Cause & Intervening Forces

Proximate Cause & Intervening Forces

1. Proximate Cause: The Scope of Foreseeable Risk

Proximate cause (legal cause) evaluates whether the physical harm suffered by the plaintiff was a reasonably foreseeable result of the defendant's negligent breach.

Defendant's Negligent Breach
  │
  ├── Foreseeable Type of Harm (Within Scope of Created Risk) ──▶ Proximate Cause Satisfied
  └── Highly Unforeseeable / Bizarre Type of Harm              ──▶ No Proximate Cause (Wagon Mound)

The Wagon Mound Rule: Foreseeability of the Harm

In the landmark decision Overseas Tankship (U.K.) Ltd. v. Morts Dock & Engineering Co., Ltd. (The Wagon Mound No. 1, 1961), the Privy Council repudiated the archaic direct-consequences rule of In re Polemis (which held a defendant liable for all direct physical results, however bizarre). Under the modern rule adopted across American jurisdictions:

• The Rule of Law: An actor is liable only for harm that is within the scope of the foreseeable risks generated by the actor's negligent conduct.
• Application in Wagon Mound: A ship negligently discharged furnace bunkering oil into Sydney Harbour. The oil drifted across the bay and coated the plaintiff's timber wharf. Two days later, molten metal dropped from welding operations onto floating cotton waste, igniting the oil and burning down the wharf. Scientific experts agreed that bunkering oil on water was not reasonably foreseeable to ignite. The court held that while fouling the slipways with oil was foreseeable, destruction by fire was an unforeseeable type of risk; therefore, proximate cause was lacking as a matter of law.

The Triad of Foreseeability: Type vs. Manner vs. Extent

To master proximate cause on the FYLSE, examinees must categorize foreseeability into three distinct dimensions:

Foreseeability Triad
├── 1. TYPE of Harm    ──▶ MUST be reasonably foreseeable (Wagon Mound)
├── 2. MANNER of Harm  ──▶ Need NOT be foreseeable (Bizarre mechanism irrelevant)
└── 3. EXTENT of Harm  ──▶ Need NOT be foreseeable (Eggshell Skull Rule)

Illustrative Scenario (Manner of Harm): A city worker negligently leaves an open, unguarded 10-foot manhole in a public sidewalk. A pedestrian carrying a box of kerosene lamps trips on the curb, drops the lamps into the hole, and the shattered kerosene lamp hits an exposed electrical cable, generating an explosive fireball that launches the pedestrian into the air. The city argues that an exploding fireball is an unforeseeable manner of injury from an open manhole. The argument fails: falling and suffering severe physical trauma is the foreseeable type of risk created by leaving an open manhole; the freakish sequence of ignition does not break proximate cause.

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2. The Eggshell Skull (Thin Skull) Rule

A universal, ironclad fixture of tort law is the Eggshell Skull Rule (also known as the Thin Skull Doctrine or Talem Qualem Rule):

Defendant Negligently Commits Minor Physical Impact
  │
  ▼
Plaintiff Possesses Latent Pre-Existing Frailty (Hemophilia, Brittle Bones, Aneurysm)
  │
  ▼
Catastrophic, Disproportionate Injury or Death Results
  │
  ▼
RULE: Defendant Takes Plaintiff as Found ──▶ FULLY LIABLE FOR ALL DAMAGES

The Rule of Law

The defendant takes the plaintiff as the defendant finds the plaintiff. If a defendant commits a negligent act that inflicts foreseeable physical impact or bodily injury upon the plaintiff, the defendant is legally liable for all resulting physical consequences, no matter how severe, unexpected, or extraordinary, and regardless of whether the magnitude of harm was foreseeable.

• Application to Pre-Existing Medical Conditions:
  • If Driver negligently rear-ends Pedestrian at 5 mph—an impact that would leave an ordinary person with a minor bruise—but Pedestrian suffers from severe latent osteoporosis or hemophilia, causing extensive internal hemorrhage, permanent paralysis, or death, Driver is liable for 100% of the catastrophic medical expenses and wrongful death damages.
  • Latent vulnerabilities include: hemophilia, latent heart disease, dormant cancer triggered by trauma, brittle bone disease (osteogenesis imperfecta), and pre-existing psychiatric fragility.
• Scope and Limitations:
  • The eggshell skull rule applies strictly to physical bodily injuries.
  • It does not apply to create initial duty or proximate cause for pure emotional distress (NIED) where a bizarre, unusually sensitive bystander suffers severe shock from conduct that would not distress a person of normal sensibilities.
  • Once a physical impact/injury occurs, the eggshell skull rule applies with full force to all physical and subsequent psychological sequelae.

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3. Intervening Forces: Dependent vs. Independent & Superseding Causes

When evaluating indirect causation, an intervening force is an external force of nature or action of a third party that enters the sequence of events after the defendant has committed the breach. Intervening forces are divided into two fundamental categories:

Intervening Forces
├── Dependent Intervening Forces (Foreseeable Responses) ──▶ DO NOT SEVER LIABILITY (D remains liable)
│     ├── Ordinary Medical Malpractice (Doctor casts broken leg improperly)
│     ├── Rescuer Intervention ("Danger invites rescue" - Rescuer injured or acts)
│     ├── Reflexive / Instinctive Reactions (Crowd flees in sudden panic)
│     └── Weakened Condition Complication (Patient on crutches slips and falls)
└── Independent Superseding Causes (Highly Extraordinary Forces) ──▶ BREAK CAUSAL CHAIN (D relieved)
      ├── Gross Medical Malpractice / Reckless Treatment (Surgeon operates intoxicated)
      ├── Unforeseeable Intentional Crimes / Torts of Third Parties (Arsonist sets fire)
      └── Extraordinary Acts of God / Natural Catastrophes (Unprecedented 500-year deluge)

Dependent Intervening Forces (Defendant Remains Liable)

A dependent intervening force is a normal, natural, or foreseeable response to the dangerous situation created by the defendant's negligence. Because these responses flow predictably from the initial peril, dependent forces DO NOT break the causal chain:

1. Subsequent Ordinary Medical Malpractice (The #1 FYLSE Trap): If a defendant's negligence causes physical injury requiring medical treatment, it is foreseeable as a matter of law that medical personnel may commit ordinary negligence during treatment. The original tortfeasor is liable for the initial injury AND the aggravated harm caused by the doctor's ordinary malpractice.
2. Rescuer Intervention ("Danger Invites Rescue"): Under Wagner v. International Ry. Co., it is foreseeable as a matter of law that third parties will attempt to rescue someone placed in peril by the defendant. The original tortfeasor is liable for injuries suffered by the rescuer, and for ordinary negligence committed by the rescuer that accidentally aggravates the victim's harm.
3. Instinctive & Escape Reactions: When an actor creates a sudden peril, reflexive human escape reactions (Scott v. Shepherd squib case) are foreseeable dependent forces; the original wrongdoer remains the proximate cause of resulting injuries.
4. Secondary Injuries & Weakened Physical Condition: If an injured plaintiff suffers a secondary injury due to their weakened condition (e.g., an accident victim using crutches slips on a clean floor because of impaired balance, fracturing a wrist), the original tortfeasor is liable for the secondary fracture.

Independent Superseding Causes (Severing Liability)

An independent intervening force operates independently of the situation created by the defendant. When an intervening force is so highly extraordinary, bizarre, and unforeseeable that the law deems it unfair to hold the original defendant liable, it is classified as a superseding cause:

1. Gross Medical Malpractice: While ordinary medical negligence is a dependent intervening force, gross medical malpractice, reckless conduct, or intentional medical abuse is an independent superseding cause that cuts off the original tortfeasor's liability for subsequent death or catastrophic worsening.
2. Unforeseeable Intentional Criminal Acts: Baseline rule: intentional criminal conduct and intentional torts of third parties are superseding causes.
3. The Foreseeable Crime Exception (Restatement (Second) of Torts § 448): An intentional criminal act DOES NOT supersede liability if the very risk of that criminal conduct was what made the defendant's act negligent in the first place (e.g., a landlord failing to fix a broken security door in a high-crime apartment building where armed robberies are frequent).
4. Extraordinary Acts of God: While ordinary seasonal weather (rain, snow, ice, wind) is foreseeable and does not break causation, an extraordinary, unprecedented natural catastrophe (an 8.5 Richter earthquake or 500-year flood) operates as a superseding cause.

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4. Master Comparison Matrix: Causation Doctrines