Causation in negligence - Legal causation: acts of God, thir...

Learning Outcomes

This article examines legal causation in negligence, including:

• Principles of legal causation and the effect of subsequent events after breach on liability
• Intervening acts (novus actus interveniens): acts of God, acts of third parties, and acts of the claimant
• Factual causation versus legal causation, and how fairness and foreseeability shape assessment of intervening events
• Criteria for when the chain of causation breaks across the main categories
• Distinguishing a chain break from contributory negligence and from apportionment of damages
• The remoteness of damage test (The Wagon Mound) and the “similar in type” approach
• The eggshell skull rule, including psychiatric vulnerability
• Application to SQE1 assessment scenarios and determination of a defendant’s liability

SQE1 Syllabus

For SQE1, you are required to understand how the chain of causation can be broken in negligence claims, and to apply the rules relating to legal causation and remoteness of damage, with a focus on the following syllabus points:

• The concept of novus actus interveniens (a new intervening act).
• How acts of God can break the chain of causation.
• When the actions of a third party will break the chain of causation.
• The circumstances in which the claimant's own actions might break the chain.
• The test for remoteness of damage (The Wagon Mound test).
• The application of the 'eggshell skull' rule.
• How deliberate or criminal third party acts are treated compared to negligent ones, and the role of foreseeability and relationship.
• Medical treatment following the initial injury and when such treatment breaks the chain (palpably wrong/grossly negligent vs ordinary negligence).
• The difference between a break in the chain and contributory negligence, and between chain break and later supervening illness.
• How the “similar in type” principle and indivisible vs divisible injury considerations operate alongside remoteness.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. What is the legal term for an intervening act that breaks the chain of causation?
2. True or False: If damage caused by a defendant's negligence is made worse by an unforeseeable natural event, the defendant is always liable for the full extent of the damage.
3. In what circumstances might the negligent act of a third party not break the chain of causation following the defendant's initial negligence?
4. What is the general principle known as the 'eggshell skull' rule?

Introduction

Establishing factual causation using the 'but for' test (covered elsewhere) is only the first step in proving causation in negligence. Even if the defendant's breach was a factual cause of the claimant's harm, the defendant may not be legally responsible if the chain of causation is broken by a subsequent event, or if the damage is considered too remote. Legal causation asks whether it is fair, just and reasonable—based on foreseeability and policy—to treat the defendant’s breach as continuing to operate when a later event contributes to the loss.

Legal causation principally involves:

• Novus actus interveniens: whether a later event is sufficiently independent and unforeseeable to displace the defendant’s responsibility for subsequent loss.
• Remoteness of damage: whether the type of damage suffered was reasonably foreseeable at the time of breach (the extent and precise manner need not be foreseeable).

A defendant remains liable for damage up to the point the chain is broken, but not for losses occurring thereafter. Conversely, if the chain is intact, the defendant may be liable even where subsequent acts or conditions aggravate the harm, subject to remoteness and the eggshell skull rule.

Key Term: Novus Actus Interveniens
A new intervening act by a third party, the claimant, or an act of God, which is significant enough to break the chain of causation between the defendant's negligent act and the claimant's loss or damage.

Whether an act breaks the chain depends on its nature and foreseeability. The main categories are acts of God, acts of third parties, and acts of the claimant.

Breaking the Chain of Causation: Novus Actus Interveniens

Sometimes, an event occurs after the defendant's breach of duty but before the claimant suffers damage, or further damage. If this subsequent event is sufficient to break the chain of causation linking the breach to the damage, it is known as a novus actus interveniens (a new intervening act). The effect is that the defendant will not be liable for the damage occurring after the intervening act, as the legal responsibility shifts.

The courts emphasise fairness and foreseeability. Put shortly, it is usually unfair to hold a defendant liable for subsequent harm caused by an independent, unforeseeable event for which they are not responsible. If the later event was foreseeable (or part of a normal sequence of consequences) then responsibility tends to remain with the original tortfeasor.

Key Term: Act of God
A natural event of exceptional and unforeseeable force (eg, earthquake, unprecedented storm) that occurs independently of human action.

Intervening Acts: Acts of God

An act of God refers to a natural event that is so extraordinary and unforeseeable that it is considered outside human control or foresight. In practice, the court asks whether the nature and severity of the natural event were reasonably foreseeable at the time of the breach, and whether the additional damage would probably have occurred regardless of the defendant’s negligence.

If such an event occurs after the defendant's breach and contributes to the claimant's damage, it may break the chain of causation, absolving the defendant from liability for the additional damage caused by the natural event. The defendant remains liable for damage caused before the intervention, and for any damage that the breach itself would inevitably have caused.

Shipping and transport cases often illustrate this principle. Where a vessel suffers negligent collision damage, and later sustains further independent heavy weather damage, the subsequent storm damage is usually treated as a distinct cause for which the original negligent defendant is not liable if the storm was not connected to the collision and would have occurred anyway.

Worked Example 1.1

A defendant negligently damages the claimant’s roof, leaving it exposed. Before repairs can be made, an exceptionally severe hurricane, unprecedented in the region, completely destroys the claimant's house. Is the defendant liable for the destruction of the house?

Answer:
Probably not. While the defendant is liable for the initial roof damage, the hurricane might be considered an unforeseeable Act of God. If its severity was truly unprecedented and unforeseeable, it would likely break the chain of causation, meaning the defendant is not liable for the house's destruction, only the initial roof damage.

Worked Example 1.2

A cargo ship is negligently damaged in a minor collision. Temporary repairs are made and the ship continues across the Atlantic, where it is later severely damaged by a storm. The storm damage is unrelated to the collision damage. Is the original negligent party liable for the later storm damage?

Answer:
No. The heavy weather damage is a separate, natural event. It is not a consequence of the earlier collision, and would have happened regardless. The storm acts as a new cause that breaks the chain for the additional damage; the original tortfeasor remains liable only for the collision damage.

Intervening Acts: Acts of Third Parties

The actions of a third party occurring after the defendant's breach can also break the chain of causation. However, this depends heavily on the foreseeability and nature of the third party's actions.

If the third party's actions were a foreseeable consequence of the defendant's negligence, the chain is unlikely to be broken. Conversely, if the third party's actions are unforeseeable, or intentionally harmful (or criminal) and outside the scope of risk created by the defendant, they may be a novus actus.

Factors the court considers include:

• The foreseeability of the third party’s intervention (e.g., would careless rescue attempts or ordinary medical treatment likely follow the accident?).
• Whether the third party’s act was negligent, reckless, or intentional and whether it was independent of the risk created by the defendant.
• Any relationship that makes the intervention more or less foreseeable (e.g., a duty to secure premises against known risks).
• Whether the defendant’s breach was still operating as a substantial cause of the loss.

Ordinary negligent medical treatment following injury is usually foreseeable and will not break the chain, unless it is “palpably wrong” or grossly negligent in a way that eclipses the original wrongdoing. Deliberate criminal acts by third parties are more likely to break the chain, but not invariably—if the defendant’s breach made such an attack likely or the defendant had a responsibility to protect against such risks, causation can be maintained.

Worked Example 1.3

Defendant A negligently leaves an excavation site unsecured. Children trespass onto the site and one falls into a trench, suffering injury. Is Defendant A liable?

Answer:
Likely yes. It is generally foreseeable that children might trespass onto unsecured sites and injure themselves. The children's actions, while technically those of a third party, are a foreseeable consequence of the defendant's initial negligence in failing to secure the site. The chain of causation is unlikely to be broken.

Worked Example 1.4

Defendant B negligently causes a minor road traffic accident, slightly damaging Claimant C's car. While they are waiting for assistance, Third Party D, driving recklessly at high speed, crashes into C's stationary car, causing significant further damage and injuring C. Is B liable for the injuries and further damage caused by D?

Answer:
Likely no. While B is liable for the initial minor damage, D's reckless driving is likely seen as a new, independent act breaking the chain of causation. B could not reasonably foresee such reckless behaviour. B would not be liable for the harm caused solely by D's intervention.

Worked Example 1.5

A contractor negligently leaves a property insecure. Overnight, squatters enter and cause extensive damage. The local authority or owner had no specific reason to anticipate entry or vandalism beyond general urban risk. Does the contractor remain liable for the squatters’ damage?

Answer:
Probably not. Deliberate acts of third parties (such as squatters causing damage) tend to break the chain where those acts are not foreseeable in the circumstances and are independent of the risk created. Absent any reason to anticipate such entry or a duty to prevent it, the intentional damage by squatters would be a novus actus.

Worked Example 1.6

After D’s negligence causes C to suffer a leg fracture, hospital doctors treat C. The treating physician makes a judgment call within accepted practice that later proves suboptimal, and C’s recovery is slower. Does D escape liability for the worsened outcome?

Answer:
No. Ordinary negligent or suboptimal medical treatment is commonly foreseeable and seldom breaks the chain. Unless the treatment is grossly negligent—palpably wrong so as to constitute a new dominant cause—the original defendant remains liable for the worsened consequences.

In contrast, where a defendant has a specific responsibility to prevent criminal interference (for example, a decorator leaving doors open contrary to instructions, enabling theft), subsequent criminal acts may be treated as foreseeable and the chain remains intact. The courts look closely at whether the defendant’s breach created the opportunity or materially increased the risk of the third party’s act.

Intervening Acts: Acts of the Claimant

A claimant's own actions after the defendant's breach can also break the chain of causation, but only if the claimant’s conduct was entirely unreasonable in the circumstances. The threshold is high. The law expects claimants to take reasonable care for their own safety; it does not penalise honest errors of judgment. If the claimant’s actions are merely careless or understandable attempts to cope with injury, responsibility is usually handled through contributory negligence (reducing damages), not chain break (eliminating liability for later harm).

The courts assess:

• The claimant’s knowledge of their condition or risk and the obviousness of the danger they undertook.
• Whether the claimant’s acts were a normal, reasonable response to the situation created by the defendant.
• The temporal proximity and the causal link between the claimant’s act and the further injury.

Examples of entirely unreasonable conduct include knowingly descending a steep staircase without support when one’s leg is prone to giving way. More sympathetic responses—walking carefully with a collar restricting vision; attempting routine tasks notwithstanding disability—do not usually break the chain.

Worked Example 1.7

Due to Defendant E's negligence, Claimant F suffers a leg injury that occasionally makes the leg give way. F is aware of this weakness. Later, F decides to descend a steep, narrow staircase without a handrail and without assistance. The leg gives way, F falls, and suffers further injury. Is E liable for the second injury?

Answer:
Unlikely. F's action in attempting to use the difficult stairs despite knowing the leg's weakness might be considered entirely unreasonable. This unreasonable conduct would constitute a novus actus interveniens, breaking the chain of causation. E would be liable for the initial leg injury but not the injury from the fall.

Worked Example 1.8

C sustains a neck injury caused by D. Because C must wear a neck collar that restricts vision, C misjudges a step on ordinary stairs and falls, aggravating the injury. Does C’s conduct break the chain?

Answer:
No. C’s conduct is a reasonable, everyday response to the original injury. The misjudgment is a foreseeable consequence of the neck collar. The chain remains intact, although contributory negligence might be argued if C’s care fell below reasonable standards.

Suicide cases illustrate the fairness-based approach: if the claimant’s suicide is the product of depressive illness caused by the defendant’s breach and impaired decision-making capacity, the chain does not break. If, however, the claimant acts voluntarily and rationally with full capacity, courts may treat the suicide as a new independent cause.

It is important to distinguish between the claimant's conduct breaking the chain of causation (which absolves the defendant of liability for subsequent damage) and contributory negligence (which reduces the damages awarded but does not eliminate liability entirely). For the claimant's act to break the chain, it must be more than merely careless; it must be unreasonable in the circumstances.

Remoteness of Damage

Even if factual causation is established and the chain of causation is unbroken, a defendant will not be liable if the damage suffered by the claimant is considered too ‘remote’ a consequence of the breach. Remoteness acts as a legal limit on the extent of a defendant’s liability.

Key Term: Remoteness of Damage
A legal principle limiting liability in negligence to types of damage that were reasonably foreseeable consequences of the defendant's breach.

The leading test for remoteness comes from Overseas Tankship (UK) Ltd v Morts Dock & Engineering Co Ltd (The Wagon Mound (No 1)) [1961] AC 388. The test is whether the type or kind of damage suffered by the claimant was reasonably foreseeable at the time of the defendant's breach.

• It is the type of harm, not the extent or manner of its occurrence, that must be foreseeable.
• If the type of harm was foreseeable, the defendant is liable even if the extent of the harm was far greater than expected.
• If the type of harm was foreseeable, the defendant is liable even if the precise way it happened was unforeseeable.

When assessing “type”, courts use a practical categorisation. Burns are a foreseeable type of injury from heat sources even if the mechanism is unusual. By contrast, a rare disease contracted via an unexpected route may be treated as not of a foreseeable type in the circumstances.

Worked Example 1.9

Defendant G negligently starts a small fire which blocks an access road. Claimant H, driving a tanker carrying flammable liquid, has to take a long detour. Due to the delay and H's unrelated heart condition, H suffers a heart attack. Is G liable for H's heart attack?

Answer:
Unlikely. While some delay or inconvenience (economic loss) might be foreseeable from blocking a road, personal injury in the form of a heart attack is likely not the type of harm reasonably foreseeable from G's negligence in starting a small fire. The damage is probably too remote.

Worked Example 1.10

Contractors leave a paraffin lamp near an open manhole, and a boy knocks it in. An unexpected explosion occurs, causing severe burns. Are burns too remote because the mechanism was unforeseeable?

Answer:
No. Burns are of a foreseeable type where flammable substances and lamps are involved. The precise mechanism (an unusual explosion) need not be foreseen. The manner and extent do not prevent recovery if the type (burns) is foreseeable.

The 'Eggshell Skull' Rule

An important exception or clarification to the remoteness rule is the 'eggshell skull' (or thin skull) rule. This principle states that the defendant must take their victim as they find them.

Key Term: Eggshell Skull Rule
The principle that a defendant is liable for the full extent of the harm suffered by a claimant, even if the severity is due to the claimant's pre-existing vulnerability or weakness, provided the initial type of harm was reasonably foreseeable.

If the type of initial injury was foreseeable, the defendant is liable for all the consequent harm, even if its extent was unforeseeable because the claimant had a particular vulnerability (eg, a brittle bone condition, a particular allergy, or even a pre-existing psychological vulnerability).

The rule applies to psychiatric vulnerability as well: if psychiatric injury would be foreseeable in a person of ordinary fortitude, the defendant bears full responsibility for the actual extent of harm suffered by a vulnerable claimant.

Worked Example 1.11

Defendant J negligently causes a minor burn to Claimant K's hand. Due to an unknown and rare pre-existing condition, K develops severe complications resulting in permanent disability. Is J liable for the full extent of the disability?

Answer:
Yes. Injury by burning was a foreseeable type of harm. Applying the eggshell skull rule, J must take K as they find them, including the rare condition. J is liable for the full extent of the disability, even though the severity of the outcome was not foreseeable.

Putting Principles Together: Supervening Events and Fairness

Two recurring patterns require attention:

• Supervening wrongs: A later wrong (e.g., assault or robbery) may aggravate the damage caused by the first wrong. Courts assess whether the later wrong is a novus actus. If it is not (because the first injury was the continuing operative cause), the first defendant remains liable despite the later event.
• Supervening illness: A later, naturally occurring disease may wholly overtake the claimant’s capacity to work. This can be treated as a novus actus interrupting the original defendant’s liability for future loss (even though the earlier injury contributed to initial loss).

Worked Example 1.12

C suffers a permanently stiff leg due to D1’s negligent driving. Before trial, C is shot in the same leg during a robbery and the leg is amputated. Is D1 still liable for loss of earnings after the amputation?

Answer:
Yes, on these facts the later assault does not replace the original injury as the operative cause of C’s impaired capacity. The robbery does not break the chain for ongoing loss; damages are assessed as if the original injury continued to be the cause.

Worked Example 1.13

E negligently injures F’s back, reducing F’s earning capacity by 50%. Three years later F develops an unrelated spinal disease that would have prevented all work. Is E liable for total loss of earnings after the disease arises?

Answer:
No. The supervening, unrelated illness breaks the chain for future loss. E remains liable for losses up to the onset of the illness but not afterwards, because the disease would have caused the total incapacity in any event.

Summary

Legal causation filters the consequences of a defendant's breach, limiting liability to those harms that are not too remote and where the chain of causation remains intact.

• Novus Actus Interveniens: A new act can break the chain if it is unforeseeable and independent.
  • Acts of God: Must be exceptional and unforeseeable natural events.
  • Acts of Third Parties: Break the chain if unforeseeable, deliberate, or reckless; do not break the chain if a foreseeable consequence of the defendant's breach. Ordinary medical treatment usually does not break the chain unless palpably wrong/grossly negligent.
  • Acts of the Claimant: Break the chain only if entirely unreasonable; the threshold is high. More commonly addressed as contributory negligence.
• Remoteness (The Wagon Mound Test): Liability is limited to damage of a type that was reasonably foreseeable at the time of the breach.
  • Type vs. Extent/Manner: Foreseeability applies to the type of harm, not its exact extent or the precise way it occurred. Burns sustained via an unusual mechanism remain recoverable where burns are a foreseeable type.
  • Eggshell Skull Rule: Defendant takes the claimant as they find them; liable for the full extent of harm if the initial type of harm was foreseeable, even if exacerbated by the claimant's vulnerability.

Understanding these principles is essential for correctly analysing liability in SQE1 negligence scenarios where events occur after the initial breach.

Key Point Checklist

This article has covered the following key knowledge points:

• Legal causation assesses whether the defendant's breach remains the operative cause of the damage despite subsequent events, with fairness and foreseeability at its core.
• A novus actus interveniens (new intervening act) can break the chain of causation.
• Acts of God (exceptional, unforeseeable natural events) can break the chain for subsequent damage.
• Acts of third parties break the chain if they are unforeseeable, independent, or intentional/criminal; they do not break the chain if they are a foreseeable consequence of the defendant’s negligence.
• Ordinary medical treatment is usually foreseeable and does not break the chain; only palpably wrong/grossly negligent treatment will do so.
• Acts of the claimant break the chain only if entirely unreasonable; otherwise the issue is addressed by contributory negligence.
• Remoteness of damage limits liability to types of harm that were reasonably foreseeable (The Wagon Mound test).
• The foreseeability test applies to the type of harm, not the extent or manner of occurrence; unusual mechanisms do not preclude liability where the type is foreseeable.
• The 'eggshell skull' rule means the defendant is liable for the full extent of foreseeable types of harm, even if exacerbated by the claimant's vulnerability.
• Supervening wrongs and illnesses are treated differently: later independent illness can break the chain for future loss, whereas some later wrongs may not if the original injury remains the operative cause.

Key Terms and Concepts

• Novus Actus Interveniens
• Act of God
• Remoteness of Damage
• Eggshell Skull Rule