Superseding Cause: A Possible Defense To Liability

Andrew M. McKenzie, Edmonds Lawyer

Generally speaking, wrongdoers are liable for the harm they cause when they breach legal duties.  But a plaintiff who sues over such wrongdoing must prove the existence of a duty, breach of that duty, causation, and damages.  Long enshrined in American common law is a principle known as superseding cause, which holds that the “chain of causation” can be broken by some outside force, usually unforeseen, which overtakes the ordinary consequences of a breach to then constitute the primary cause of damages.  When a superseding cause is responsible for a plaintiff’s damages, the defendant who breached the underlying duty is generally not liable for those damages and may raise superseding cause as a defense to liability.  In Washington, to determine whether an intervening act constitutes a superseding cause, courts consider whether: (1) the intervening act created a different type of harm than otherwise would have resulted from the actor’s negligence; (2) the intervening act was extraordinary or resulted in extraordinary consequences; and (3) the intervening act operated independently of any situation created by the actor’s negligence.  The act has to be “so highly extraordinary or unexpected that it can be said to fall out of the realm of reasonable foreseeability as a matter of law, and if the acts are within the ambit of hazards covered by the duty imposed upon the defendant, they are foreseeable and do not supersede the defendant’s negligence.”  Juries normally decide whether a third party’s intervening act rises to the level of a superseding cause.  But sometimes, the facts can be so clear that the matter may be resolved via summary judgment without a trial at all (see my webinar about summary judgment here:

A recent published case, Adgar v. Dinsmore et al., illustrates how the defense of superseding cause can play out and what sorts of fact patterns test the defense’s limits in Washington.  There, a water district worker left a service truck running and unattended with the driver side door open when an intoxicated suicidal resident nearby (Dinsmore) stole it, drove recklessly, and struck the plaintiff’s vehicle, causing severe injuries.  The worker’s employer, Lakewood Water District (“LWD”), raised the defense of superseding cause, claiming that Dinsmore’s act to commit suicide by stealing the truck broke the chain of causation and that LWD did not owe the plaintiff a duty of care.  The trial court agreed that superseding cause applied, but the Court of Appeals reversed.  Relying in large part on the fact that the truck was left running in a public right of way (as opposed to a private driveway), the Court of Appeals held that LWD owed plaintiff a duty of care.  On the issue of superseding cause, the Court of Appeals rejected the defense.  First, the Court held that Dinsmore’s intervening acts did not create a different type of harm than would have otherwise resulted from LWD’s alleged negligence, because leaving the truck running with the driver’s side door open after observing Dinsmore in close proximity and appearing intoxicated, created a high degree of risk of harm that Dismore would steal the truck and cause a collision in an intoxicated state.  Second the collision was an “ordinary consequence” of an intoxicated person stealing a truck.  Third, Dinsmore’s intervening acts were “activated” by the worker’s affirmative act of leaving the truck running with the door open and unattended.  The Court rejected LWD’s argument that intentional intervening acts (such as attempted suicide) must constitute superseding cause.  In so holding, the Court held that foreseeability, rather than intentionality, is the deciding factor.

Adgar demonstrates that the question of whether superseding cause applies will not always be clear.  Even intentional acts by third parties may not be enough by themselves to preclude liability.  Arguably, Adgar is a highly unusual case that could have limited effect on the body of case law applying superseding cause; the worker’s observation of Dinsmore in an apparently intoxicated state likely had a lot to do with the Court’s holding.  Nevertheless, prudent litigation involves appreciating risk and uncertainty.

The lawyers at Beresford Booth have a wealth of experience with commercial litigation.  We would be happy to assist you in litigating cases which may involve the defense of superseding cause.

To Learn More about Superseding Cause please do not hesitate to contact us at or by phone (425) 776-4100 for assistance.

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