Legal Definitions - intervening cause

An intervening cause is a new, independent event that occurs after an initial wrongful action but before the ultimate harm or injury takes place. This new event is significant because it disrupts the natural sequence of events that would have otherwise linked the original action directly to the resulting harm. When an intervening cause is present, it can effectively "break the chain of causation," meaning the person who committed the initial wrongful act may no longer be considered legally responsible for the final injury, as the intervening cause is seen as the more direct or immediate reason for the harm.

Here are some examples to illustrate this concept:

• Example 1: Car Accident and Subsequent Ambulance Crash

  Imagine a driver (Driver A) negligently runs a stop sign, causing a minor collision with another car (Driver B). Driver B sustains whiplash and a broken arm from this initial impact. While Driver B is being transported to the hospital in an ambulance, the ambulance is struck by a drunk driver (Driver C) who swerves into its lane. As a result of this second collision, Driver B suffers a severe spinal injury, leading to paralysis.

  How it illustrates the term: Driver A would likely be held responsible for the whiplash and broken arm sustained in the initial collision. However, the drunk driver's actions (Driver C) constitute an intervening cause for the paralysis. This new, independent, and unforeseeable event broke the chain of causation between Driver A's initial negligence and the much more severe spinal injury. Consequently, Driver C, not Driver A, would likely be considered primarily responsible for the paralysis.

• Example 2: Negligent Construction and Unforeseeable Natural Disaster

  Consider a construction company that builds a retaining wall on a hillside, but negligently uses substandard materials and fails to reinforce the foundation according to standard geological recommendations for the area. Months later, a sudden, unprecedented landslide, triggered by an extremely rare geological shift that no reasonable expert could have predicted or prepared for, causes the building to collapse.

  How it illustrates the term: While the construction company's initial negligence in foundation reinforcement was a contributing factor, the unforeseeable and extraordinary landslide acts as an intervening cause. If the building would have remained stable under all *foreseeable* conditions and typical geological stresses, the landslide breaks the direct causal link between the developer's initial negligence and the ultimate collapse. This could potentially reduce or eliminate the developer's liability for the collapse itself, shifting responsibility to the force of nature.

• Example 3: Medical Malpractice and Subsequent Misdiagnosis

  A surgeon performs an operation and negligently leaves a surgical sponge inside a patient's abdomen. Weeks later, the patient develops a severe infection. During a follow-up visit, a different doctor misdiagnoses the infection as a common stomach virus and prescribes an ineffective treatment, leading to a much more severe, life-threatening condition that requires extensive additional surgery.

  How it illustrates the term: The original surgeon is clearly responsible for the initial error of leaving the sponge. However, the second doctor's negligent misdiagnosis and ineffective treatment could be considered an intervening cause for the *escalated* and *life-threatening* condition. While the sponge was the initial problem, the second doctor's independent and negligent actions significantly worsened the patient's prognosis, potentially breaking the chain of causation for the most severe outcomes from the original surgeon's initial error.