1. Core Rule
A defendant who acts negligently remains liable for harm that is a foreseeable result of that negligence, even when a third party’s ordinary negligence also contributes to the injury.
The presence of a negligent third party does not automatically break the chain of causation. Liability is avoided only when the intervening act is extraordinary, unforeseeable, or intentional, rising to the level of a superseding cause.
2. Foreseeability Controls Liability
Negligence law is grounded in foreseeability, not exclusivity of fault.
A defendant is responsible for:
- Harm that falls within the scope of the risk created by their conduct
- Injuries that are a natural and probable consequence of the original negligence
If it is foreseeable that another person might act negligently in response to the defendant’s conduct, that negligence is treated as a concurrent cause, not a superseding one.
3. Ordinary Negligence by Third Parties Is Foreseeable
Courts consistently recognize that:
- People make mistakes
- Drivers drive carelessly
- Employees act inattentively
- Medical providers commit non-gross errors
Because ordinary negligence is common and predictable, it is considered foreseeable as a matter of law.
Therefore:
A negligent defendant takes the risk that others may also act negligently.
4. Intervening vs. Superseding Causes
The critical distinction is between:
Intervening Cause
- Occurs after the defendant’s negligence
- Contributes to the harm
- Is foreseeable
- Does NOT relieve the defendant of liability
Superseding Cause
- Occurs after the defendant’s negligence
- Is extraordinary or unforeseeable
- Breaks the causal chain
- Relieves the defendant of liability
Ordinary negligence by a third party almost always falls into the intervening, not superseding, category.
5. Practical Examples
Example 1: Traffic Hazard
A contractor negligently leaves debris on a roadway.
A driver, speeding slightly, hits the debris and injures a pedestrian.
Result:
- Contractor remains liable
- Driver’s ordinary negligence is foreseeable
- Fault is apportioned, not eliminated
Example 2: Unsafe Premises
A landlord fails to repair broken stairs.
A delivery driver trips due to minor inattention and falls.
Result:
- Landlord is liable
- Inattention is foreseeable
- Comparative fault may reduce damages, not bar recovery
Example 3: Medical Chain
A defendant causes an accident.
A physician commits a routine diagnostic error during treatment.
Result:
- Original tortfeasor remains liable
- Ordinary medical negligence is foreseeable
- Only gross malpractice might qualify as superseding
6. Comparative Fault Does Not Erase Liability
Modern comparative fault systems:
- Allocate responsibility
- Do not require exclusive causation
- Preserve liability for all substantial contributing causes
Thus, the presence of a negligent third party typically leads to apportionment of damages, not dismissal of claims against the original defendant.
7. Policy Rationale
This rule exists to:
- Prevent negligent actors from escaping liability due to predictable human error
- Encourage safer conduct by accounting for real-world behavior
- Protect injured parties from gaps in responsibility
If ordinary negligence could erase liability, defendants would benefit from the very risks they helped create.
8. Conclusion
A negligent defendant cannot avoid responsibility simply because someone else was also negligent.
So long as:
- The injury was foreseeable, and
- The third party’s conduct was ordinary negligence,
the original defendant remains liable.
Only extraordinary, unforeseeable, or intentional misconduct by a third party breaks the chain of causation.