Proximate cause

In the law, a proximate cause is an event sufficiently related to a legally recognizable injury to be held to be the cause of that injury. There are two types of causation in the law: cause-in-fact, and proximate (or legal) cause. Cause-in-fact is determined by the "but for" test: But for the action, the result would not have happened. For example, but for running the red light, the collision would not have occurred. The action is a necessary condition, but may not be a sufficient condition, for the resulting injury. For an act to cause a harm, both tests must be met; proximate cause is a legal limitation on cause-in-fact.

The formal Latin term for "but for" (cause-in-fact) causation, is sine qua non causation.

A few circumstances exist where the "but for" test is complicated, or the test is ineffective. The primary examples are:

Since but-for causation is very easy to show and does not assign culpability (but for the rain, you would not have crashed your car – the rain is not morally or legally culpable but still constitutes a cause), there is a second test used to determine if an action is close enough to a harm in a "chain of events" to be a legally culpable cause of the harm. This test is called proximate cause.

There are several competing theories of proximate cause.

The most common test of proximate cause under the American legal system is foreseeability. It determines if the harm resulting from an action could reasonably have been predicted. The test is used in most cases only in respect to the type of harm. It is foreseeable, for example, that throwing a baseball at someone could cause them a blunt-force injury. But proximate cause is still met if a thrown baseball misses the target and knocks a heavy object off a shelf behind them, which causes a blunt-force injury. Evident in Corrigan v HSE (2011 IEHC 305).

This is also known as the "extraordinary in hindsight" rule.

Direct causation is a minority test, which addresses only the metaphysical concept of causation. It does not matter how foreseeable the result as long as what the negligent party's physical action can be tied to what actually happened. The main thrust of direct causation is that there are no intervening causes between an act and the resulting harm. An intervening cause has several requirements: it must 1) be independent of the original act, 2) be a voluntary human act or an abnormal natural event, and 3) occur in time between the original act and the harm.

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Wikipedia