Novus actus interveniens

Latin for ‘new act intervening’, novus actus interveniens (in a tortious action for negligence) is any intervening act that can sever the legal connection between a defendant’s actions and the harm suffered by the plaintiff, with the effect that the defendant cannot be deemed legally responsible for the plaintiff’s harm.

Simply put, novus actus interveniens serves to break the chain of causation between a defendant’s wrongful act or omission and the harm suffered by the plaintiff.

To determine whether or not an occurrence or act will carry the legal weight of novus actus interveniens, it must ordinarily be either:

1. A human action that is properly to be regarded as voluntary; or
2. A causally independent event, the conjunction of which with the wrongful act or omission is by ordinary circumstances so extremely unlikely as to be termed a coincidence.

The authority for this test is Haber v Walker (1963).

An example of a voluntary human action that could break the chain of causation for negligence may be where a plaintiff who has suffered a minor leg injury due to the defendant’s negligence decides to jump off a roof, breaking their leg. Here, the voluntary human action of the plaintiff would sever the connection between the defendant’s actions and the harm now suffered. A voluntary human action by a third party could also break the chain of causation – e.g. if the plaintiff with the minor leg injury was shot in the leg by a third party, that would also sever the connection between the defendant’s actions and the harm now suffered.

An example of a causally independent event that could break the chain of causation for negligence may be where a plaintiff who has suffered a minor leg injury due to the defendant’s negligence is struck in that same leg by an asteroid from space. Here, the causally independent event would sever the connection between the defendant’s actions and the harm now suffered.