Novus actus interveniens is Latin for a new intervening act. In the Law of Delict 6th Edition, Neethling states that a Novus actus interveniens is an independent event which, after the wrongdoer's act has been concluded either caused or contributed to the consequence concerned. A novus actus breaks the causal chain between the initial wrongdoer's action and the liability that is imputed to him or her as a result thereof.

A requirement for an act or omission committed after the initial wrongdoer's act to constitute a Novus actus is that the secondary act was not reasonably foreseeable. If the subsequent event was reasonably foreseeable at the time of the initial wrongful act, it is not to be considered as a novus actus capable of limiting the liability to be imputed on the initial wrongdoer.

As a general rule, the damage is said to be too remote where it is caused by the intervening act of human volition of a third party, or when the injury to the plaintiff might have been occasioned by the intervening act of volition on the part of the plaintiff himself. The question of whether an initially negligent person, would be liable for all the consequences ad infinitum, expected or unexpected, probable or improbable, depends for its answer upon the application of a further test which has recently come into prominence, that is, the test of isolation.

According to this test, where the wrongful act is isolated from the consequences is deemed to have been snapped, and the defendant ceases to be liable for such consequences as having arisen after the intervention of that other act of human violation. The prior act having exhausted itself the chain of causation has in contemplation of law been broken and the wrongdoer can no longer be held responsible for further consequence.

A Novus actus is not confined to either factual or legal causation only and can interrupt the causal chain at either point. In respect of factual causation, a novus actus interrupts the nexus between the wrongful act of the initial wrongdoer and the consequences of his act to such an extent that it frees him of the liability of his actions.

However, when assessing novus actus in respect of legal causation, regard must be had to the aspects of policy, fairness, reasonableness, and justice in order to determine whether liability for the initial wrongful act can still be imputed to the initial wrongdoer and whether the causal chain has been broken. A Novus actus, therefore, disrupts the directness aspect of the initial act and the subjective test of legal causation cannot be fulfilled.

As a novus actus is an independent intervening act, it can be occasioned by anyone or anything other than the initial wrongdoer. This general category also includes the injured party himself or herself, another third party, or even an act of God. Therefore, an injured patient who walks on a slippery floor after having been injured thereafter occasioning further surgery will have created his own Novus actus, or where a storm causes further and greater damage to a property after it has been damaged by a wrongdoer will also be viewed as a Novus actus.

In Weld Bundell b. Stephens, The appellant employed the respondent, a chartered accountant to investigate the affairs of a company. He gave written instructions which contained matter which was libelous of two officials of the company. Respondent passed these instructions to his partner, who carelessly left them on the floor at the company's office.

The company's manager found them and communicated their contents to the officials who then recovered damages for the libel from the appellant. In the instant action, the appellant could recover nominal damages only. He could not recover upon the basis of an indemnity for his actual loss in the libel action because the manager's action was the voluntary act of a free agent over whom the appellant had no control, for whose actions he was not answerable.

Exceptions to the rule of Novus actus interveniens:

1. Where the intervening act has been intentionally procured by the defendant.
2. Where the intervening actor is not fully responsible.
3. Where the intervening act is such as could be reasonably anticipated.
4. Where the intervening act is a mere reflex or involuntary action.

Conclusion:
To determine whether or not an occurrence or act will carry the legal weight of Novus actus interveniens, it must ordinarily be either: -A human action that is properly to be regarded as voluntary; or -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. Voluntary human action by a third party could also break the chain of causation.

e.g. if the plaintiff with the minor leg injury were shot in the leg by a third party, that would also sever the connection between the defendant’s actions and the harm now suffered.