California Bar Causation
Last updated: May 2, 2026
Causation questions are one of the highest-leverage areas to study for the California Bar. This guide breaks down the rule, the elements you need to recognize, the named traps that catch most students, and a memory aid that scales to test day. Read it once, then practice the same sub-topic adaptively in the app.
The rule
To prevail on a negligence claim, the plaintiff must prove both actual cause (cause-in-fact) and proximate cause (legal cause). Actual cause is generally established by the but-for test: but for the defendant's breach, the plaintiff would not have been injured. Where two or more independent forces each would have caused the harm, courts apply the substantial factor test (Restatement (Second) of Torts § 431). Proximate cause limits liability to harms whose risk made the defendant's conduct negligent — typically the foreseeable scope of the risk created (Restatement (Third) of Torts § 29). Intervening causes that are foreseeable do not break the chain; superseding causes (unforeseeable intervening forces) cut off liability.
Elements breakdown
But-For Causation (Cause-in-Fact, default test)
The defendant's breach was a necessary antecedent to the plaintiff's harm.
- Plaintiff suffered legally cognizable harm
- Defendant breached a duty of care
- Harm would not have occurred absent the breach
- Causal link traceable in time and physical sequence
Substantial Factor Test (Multiple Sufficient Causes)
Used when two or more independent causes each would have been sufficient to produce the harm, making but-for analysis fail.
- Two or more causes operating concurrently
- Each cause independently sufficient to produce harm
- Defendant's conduct was a substantial contributing factor
- Harm is indivisible or commingled
Common examples:
- Two negligently set fires merging and burning plaintiff's home
- Two polluters each discharging enough toxin to kill fish
- Concurrent negligent acts producing single indivisible injury
Alternative Liability (Summers v. Tice doctrine)
Burden of proof on causation shifts to multiple defendants when all acted negligently but plaintiff cannot identify which one caused the harm.
- All defendants acted tortiously toward plaintiff
- Only one (or some) actually caused plaintiff's harm
- Plaintiff cannot identify the specific tortfeasor
- All possible tortfeasors joined as defendants
Loss-of-Chance Doctrine
In medical malpractice, plaintiff may recover for the reduced chance of survival or recovery proximately caused by defendant's negligence, even if pre-existing chance was below 50%.
- Defendant negligently failed to diagnose or treat
- Plaintiff had a measurable pre-existing chance of better outcome
- Defendant's breach reduced that chance
- Damages proportional to chance lost
Common examples:
- Misread tumor scan reducing 40% survival chance to 15%
- Delayed diagnosis of treatable infection
- Failure to refer to specialist within window
Proximate Cause — Foreseeability (Risk Rule)
Liability extends only to harms within the scope of the risk that made the defendant's conduct negligent.
- Type of harm reasonably foreseeable
- Class of plaintiff within zone of foreseeable danger
- No superseding unforeseeable intervening cause
- Harm not too remote in time, space, or causal sequence
Foreseeable Intervening Causes (No Break in Chain)
Intervening forces that are reasonably foreseeable do not cut off the original tortfeasor's liability.
- Original defendant's negligence created risk
- Intervening force occurred after breach
- Intervening force was foreseeable type
- Plaintiff's harm flowed from combined sequence
Common examples:
- Subsequent medical malpractice treating original injury
- Negligent rescue of person endangered by defendant
- Foreseeable criminal conduct in high-crime area defendant ignored
- Reaction injuries from fleeing defendant's hazard
Superseding Causes (Break in Chain)
Unforeseeable intervening forces that relieve the original defendant of liability for ensuing harm.
- Intervening force arose after defendant's breach
- Force was unforeseeable in type and manner
- Force was independent (not produced by defendant's act)
- Force was the direct cause of ultimate harm
Common examples:
- Unforeseeable intentional criminal conduct
- Acts of God of extraordinary character
- Grossly abnormal medical treatment producing new injury
- Unforeseeable third-party deliberate sabotage
Eggshell-Plaintiff Rule
Defendant takes the plaintiff as found; unforeseeable extent of harm does not defeat proximate cause once any harm of the foreseeable type was foreseeable.
- Defendant's conduct was tortious
- Some harm of the relevant type was foreseeable
- Plaintiff suffered greater harm due to pre-existing condition
- Extent of harm need not be foreseeable
Common patterns and traps
The But-For/Proximate Conflation
Distractors confuse the two causation tests, treating proximate cause as a question of physical chain and but-for as a question of foreseeability. The correct analysis applies but-for as a mechanical necessary-condition test and proximate cause as a normative scope-of-risk filter. Choices that say 'no proximate cause because the injury would not have occurred but for X' are diagnostically miscategorizing the test.
An answer choice that resolves a foreseeability dispute by reciting 'but for' language, or resolves a multiple-cause problem by reciting 'proximate cause' language.
The Sufficient-Cause Trap (Substantial Factor Missed)
When two independent forces each would have caused the harm, the but-for test produces the wrong answer because neither defendant is a but-for cause (the harm would have occurred anyway from the other force). Candidates who recite the default rule mechanically conclude 'no causation' and miss that the substantial factor test governs. The Restatement (Second) § 432(2) and Third § 27 both supply the rule.
A choice that says 'no liability because plaintiff's harm would have occurred anyway from the other negligent fire/polluter/source,' applied to merged-cause facts.
The Superseding-Cause Overreach
Distractors label any intervening third-party act as 'superseding' to insulate the original tortfeasor. The actual rule is narrow: the intervening force must be unforeseeable in kind, not merely unexpected in detail. Subsequent medical negligence, negligent rescue, foreseeable criminal acts on premises with known crime risk, and reaction injuries are all foreseeable as a class.
A choice asserting that the original defendant is not liable 'because the doctor's negligence was a superseding cause' or 'because the subsequent criminal act broke the chain.'
The Eggshell Misapplication
Candidates either over-apply the eggshell rule (using it to manufacture foreseeability where the type of harm itself was unforeseeable) or under-apply it (denying recovery because the extent of harm was unforeseeable). The rule operates only on extent, not on the threshold question whether any harm of the foreseeable type would result.
A choice denying recovery 'because defendant could not have foreseen plaintiff's hemophilia,' offered against facts where physical injury of the type suffered was clearly foreseeable.
The Loss-of-Chance Pre-Existing-Condition Trap
In medical malpractice with a pre-existing low-survival-chance condition, distractors invoke 'plaintiff would have died anyway' to deny causation entirely. Many jurisdictions (and California recognizes the doctrine in narrow circumstances) allow recovery for the lost chance itself, with damages proportional to the chance reduced.
A choice that says 'no causation because plaintiff had only a 30% chance of survival even with proper diagnosis,' applied to negligent-misdiagnosis facts.
How it works
Causation is the negligence element where most exam points are won and lost because it has two independent components and candidates routinely conflate them. Suppose Reyes runs a stop sign and clips Liu's car; Liu is taken to County Hospital where Dr. Patel negligently administers the wrong medication, worsening Liu's injuries. Actual cause asks the mechanical question: but for Reyes's running the stop sign, would Liu have been injured? No — so actual cause is satisfied. Proximate cause then asks the policy question: is the worsened condition within the scope of risk Reyes's negligence created? Yes — subsequent medical malpractice on a person injured by the defendant is a classic foreseeable intervening cause, so Reyes is liable for the aggravated harm too. If instead a meteor struck the ambulance, that would be a superseding cause cutting off Reyes's liability for harms beyond the original collision. The eggshell rule then handles the case where Liu has an unusually fragile spine that turns a fender-bender into paraplegia: foreseeability of extent is irrelevant once any harm of the relevant type was foreseeable.
Worked examples
How should the court rule on Reyes's motion?
- A Grant the motion, because Patel cannot establish but-for causation when the lightning fire alone would have produced the same harm.
- B Grant the motion, because lightning is an act of God that supersedes Reyes's negligence as a matter of law.
- C Deny the motion, because Reyes's conduct was a substantial factor in producing Patel's indivisible harm. ✓ Correct
- D Deny the motion, because under the eggshell-plaintiff rule Reyes takes Patel as he finds him.
Why C is correct: This is the textbook merged-fires fact pattern that triggers the substantial factor test from Restatement (Second) of Torts § 432(2) and Third § 27. When two independent forces each would have been sufficient to produce indivisible harm, the but-for test produces an absurd result (neither cause is necessary), so courts ask whether each defendant's conduct was a substantial contributing factor. Reyes's negligently set fire merged with the lightning fire and contributed to destroying the barn, satisfying the substantial factor standard.
Why each wrong choice fails:
- A: This applies the default but-for test mechanically to a fact pattern that defeats it. The whole point of the substantial factor doctrine is to avoid the unjust no-causation result that but-for produces when independent sufficient causes merge. (The Sufficient-Cause Trap (Substantial Factor Missed))
- B: Lightning is a natural force, but its presence does not supersede a concurrent negligent cause when both forces independently would have produced the same harm; the proper analysis is concurrent causation, not superseding cause. Superseding causes operate sequentially after defendant's breach, not simultaneously alongside it. (The Superseding-Cause Overreach)
- D: The eggshell-plaintiff rule addresses the unforeseeable extent of harm to a vulnerable plaintiff, not the existence of multiple sufficient causes. The rule has no application here because Patel's barn has no special vulnerability — the issue is concurrent causation by independent forces. (The Eggshell Misapplication)
How should the court rule on Patel's motion?
- A Grant the motion, because Dr. Mendoza's independent negligence is a superseding cause as a matter of law.
- B Grant the motion, because Patel could not have foreseen the specific manner in which Dr. Mendoza would breach her standard of care.
- C Deny the motion, because subsequent medical negligence in treating an injury caused by defendant is a foreseeable intervening cause. ✓ Correct
- D Deny the motion, because Patel and Dr. Mendoza are joint tortfeasors and Patel is therefore strictly liable for all downstream harm.
Why C is correct: Subsequent negligent medical treatment of an injury the original tortfeasor caused is the canonical example of a foreseeable intervening cause that does not break the chain of proximate causation (Restatement (Second) of Torts § 457). The original defendant remains liable for the aggravated harm because such malpractice is foreseeable as a class — that the injured plaintiff will seek medical care, and that medical care is sometimes negligent, is exactly the kind of risk Patel's negligence set in motion.
Why each wrong choice fails:
- A: This overstates the superseding-cause doctrine, which is narrow and reserved for unforeseeable intervening forces. Subsequent medical negligence is foreseeable as a class even though no one can predict the specific manner of the malpractice; it is a paradigm foreseeable intervening cause. (The Superseding-Cause Overreach)
- B: Foreseeability for proximate cause purposes operates at the level of the type or class of harm, not the specific manner of breach. The Restatement and Wagon Mound line of cases ask whether the general category (medical complications from accident treatment) was foreseeable, not whether the precise mistake was predictable. (The But-For/Proximate Conflation)
- D: Joint tortfeasor analysis allocates liability among multiple defendants but does not impose strict liability on negligence defendants. The basis for Patel's liability for the aggravated harm is foreseeable proximate causation, not a strict-liability rule, and joint-and-several liability is the wrong doctrinal label here. (The But-For/Proximate Conflation)
Will Singh likely prevail?
- A No, because Okafor's deliberate criminal conduct is always a superseding cause that breaks the chain of proximate causation.
- B No, because Garcia owed no duty to Singh, an adjacent landowner with whom he had no contractual relationship.
- C Yes, because criminal conduct on inadequately secured premises with prior similar incidents is a foreseeable intervening cause within the scope of the risk Garcia's negligence created. ✓ Correct
- D Yes, because Garcia is strictly liable as a matter of law for storage of flammable solvents under the abnormally dangerous activity doctrine.
Why C is correct: Criminal acts of third parties are generally treated as superseding only when unforeseeable, but where the defendant's negligence created the very opportunity for the criminal act and prior similar incidents put the defendant on notice, the criminal conduct falls within the scope of the foreseeable risk and does not cut off liability (Restatement (Third) of Torts § 19; see scope-of-risk doctrine). The three prior trespasses through the same gap make Okafor's conduct foreseeable as a class.
Why each wrong choice fails:
- A: This states the superseding-cause rule too broadly. Deliberate criminal conduct can be a superseding cause when unforeseeable, but where defendant's negligence created the very opportunity and prior incidents established foreseeability, the criminal act is a foreseeable intervening cause that preserves liability. (The Superseding-Cause Overreach)
- B: A landowner owes a duty of reasonable care to avoid creating unreasonable risks of harm to neighboring properties; no contractual relationship is required. The duty question here is satisfied — the dispute is about causation, not duty. (The But-For/Proximate Conflation)
- D: Storage of flammable solvents in an industrial setting is generally not categorized as an abnormally dangerous activity triggering strict liability under Restatement (Third) of Torts § 20, particularly in zoned industrial parks where such storage is common. The basis for Garcia's liability is negligence with foreseeable proximate causation, not strict liability. (The But-For/Proximate Conflation)
Memory aid
Causation has TWO gates: (1) BUT-FOR (or substantial factor when two sufficient causes merge), then (2) FORESEEABILITY of harm-type. Memorize the four classic foreseeable intervening causes — 'Medical malpractice, Negligent rescue, Reaction injury, Subsequent disease/accident' (M-N-R-S) — these never break the chain.
Key distinction
Foreseeable intervening cause (does NOT cut off liability) versus unforeseeable superseding cause (DOES cut off liability). Subsequent medical negligence treating the very injury defendant caused is foreseeable per se; deliberate criminal conduct unrelated to defendant's risk is generally superseding unless defendant's negligence created the opportunity (e.g., leaving keys in car in high-theft area).
Summary
Negligence causation requires both factual causation (but-for, or substantial factor when causes merge) and proximate causation (harm within the foreseeable scope of risk), with foreseeable intervening causes preserving liability and unforeseeable superseding causes cutting it off.
Practice causation adaptively
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Start your free 7-day trialFrequently asked questions
What is causation on the California Bar?
To prevail on a negligence claim, the plaintiff must prove both actual cause (cause-in-fact) and proximate cause (legal cause). Actual cause is generally established by the but-for test: but for the defendant's breach, the plaintiff would not have been injured. Where two or more independent forces each would have caused the harm, courts apply the substantial factor test (Restatement (Second) of Torts § 431). Proximate cause limits liability to harms whose risk made the defendant's conduct negligent — typically the foreseeable scope of the risk created (Restatement (Third) of Torts § 29). Intervening causes that are foreseeable do not break the chain; superseding causes (unforeseeable intervening forces) cut off liability.
How do I practice causation questions?
The fastest way to improve on causation is targeted, adaptive practice — working questions that focus on your specific weak spots within this sub-topic, getting immediate feedback, and revisiting items you missed on a spaced-repetition schedule. Neureto's adaptive engine does this automatically across the California Bar; start a free 7-day trial to see your sub-topic mastery climb in real time.
What's the most important distinction to remember for causation?
Foreseeable intervening cause (does NOT cut off liability) versus unforeseeable superseding cause (DOES cut off liability). Subsequent medical negligence treating the very injury defendant caused is foreseeable per se; deliberate criminal conduct unrelated to defendant's risk is generally superseding unless defendant's negligence created the opportunity (e.g., leaving keys in car in high-theft area).
Is there a memory aid for causation questions?
Causation has TWO gates: (1) BUT-FOR (or substantial factor when two sufficient causes merge), then (2) FORESEEABILITY of harm-type. Memorize the four classic foreseeable intervening causes — 'Medical malpractice, Negligent rescue, Reaction injury, Subsequent disease/accident' (M-N-R-S) — these never break the chain.
What's a common trap on causation questions?
Conflating but-for with proximate cause
What's a common trap on causation questions?
Treating any intervening act as superseding
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