Proximate cause
In law and insurance, a proximate cause is an event sufficiently related to an injury that the courts deem the event 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. A few  circumstances exist where the but for test is ineffective (see But-for test). Since but-for causation is very easy to show (but for stopping to tie your shoe, you would not have missed the train and would not have been mugged), a second test is used to determine if an action is close enough to a harm in a "chain of events" to be legally valid. This test is called proximate cause. Proximate cause is a key principle of Insurance and is concerned with how the loss or damage actually occurred. There are several competing theories of proximate cause  (see Other factors). For an act to be deemed 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. But-for test. 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 carthe 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, from the Latin "proxima causa". Other factors. There are several competing theories of proximate cause. Foreseeability. 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. This is also known as the "extraordinary in hindsight" rule. Direct causation. 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 activity 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. Direct causation is the only theory that addresses only causation and does not take into account the culpability of the original actor. Risk enhancement/causal link. The plaintiff must demonstrate that the defendant's action increased the risk that the particular harm suffered by  the plaintiff would occur. If the action were repeated, the likelihood of the harm would correspondingly increase. This is also called foreseeable risk. Harm within the risk. The harm within the risk (HWR) test determines whether the victim was among the class of persons who could foreseeably be harmed, and whether the harm was foreseeable within the class of risks. It is the strictest test of causation, made famous by Benjamin Cardozo in "Palsgraf v. Long Island Railroad Co." case under New York state law. The first element of the test is met if the injured person was a member  of a class of people who could be expected to be put at risk of injury by the action. For example, a pedestrian, as an expected user of sidewalks, is among the class of people put at risk by driving on a sidewalk, whereas a driver who is distracted by another driver driving on the sidewalk, and consequently crashes into a utility pole, is not. The HWR test is no longer much used, outside of New York law. When it is used, it is used to consider the class of people injured, not the type of harm. The main criticism  of this test is that it is preeminently concerned with culpability, rather than actual causation. The "Risk Rule". Referred to by the Reporters of the Second and Third Restatements of the Law of Torts as the "scope-of-the-risk" test, the term "Risk Rule" was coined by the University of Texas School of Law's Dean Robert Keeton. The rule is that “[a]n actor’s liability is limited to those physical harms that result from the risks that made the actor’s conduct tortious.” Thus, the operative question is "what were the particular risks that made an actor's  conduct negligent?" If the injury suffered is not the result of one of those risks, there can be no recovery. Two examples will illustrate this principle: The notion is that it must be the risk associated with the negligence of the conduct that results in an injury, not some other risk invited by aspects of the conduct that in of themselves would not be negligent. Controversy. The doctrine of proximate cause is notoriously confusing. The doctrine is phrased in the language of causation, but in most of the cases in which proximate cause is actively litigated, there is not much  real dispute that the defendant but-for caused the plaintiff's injury. The doctrine is actually used by judges in a somewhat arbitrary fashion to limit the scope of the defendant's liability to a subset of the total class of potential plaintiffs who may have suffered some harm from the defendant's actions. For example, in the two famous "Kinsman Transit" cases from the 2nd Circuit (exercising admiralty jurisdiction over a New York incident), it was clear that mooring a boat improperly could lead to the risk of that boat drifting away and crashing into another boat, and that  both boats could crash into a bridge, which collapsed and blocked the river, and in turn, the wreckage could flood the land adjacent to the river, as well as prevent any traffic from traversing the river until it had been cleared. But under proximate cause, the property owners adjacent to the river could sue ("Kinsman I"), but not the owners of the boats or cargoes which could not move until the river was reopened ("Kinsman II"). Therefore, in the final version of the "Restatement (Third), Torts: Liability for Physical and Emotional Harm", published in 2010, the American Law Institute argued  that proximate cause should be replaced with scope of liability. Chapter 6 of the Restatement is titled "Scope of Liability (Proximate Cause)." It begins with a special note explaining the institute's decision to reframe the concept in terms of "scope of liability" because it does not involve true causation, and to also include "proximate cause" in the chapter title in parentheses to help judges and lawyers understand the connection between the old and new terminology. The Institute added that it "fervently hopes" the parenthetical will be unnecessary in a future fourth Restatement of Torts. Efficient proximate cause. A related  doctrine is the insurance law doctrine of efficient proximate cause. Under this rule, in order to determine whether a loss resulted from a cause covered under an insurance policy, a court looks for the predominant cause which sets into motion the chain of events producing the loss, which may not necessarily be the "last" event that immediately preceded the loss. Many insurers have attempted to contract around efficient proximate cause through the use of "anti-concurrent causation" (ACC) clauses, under which if a covered cause and a noncovered cause join to cause a loss, the loss is not covered. ACC  clauses frequently come into play in jurisdictions where property insurance does not normally include flood insurance and expressly excludes coverage for floods. The classic example of how ACC clauses work is where a hurricane hits a building with wind and flood hazards "at the same time." If the evidence later shows that the wind blew off a building's roof and then water damage resulted only because there was no roof to prevent rain from entering, there would be coverage, but if the building was simultaneously flooded (i.e., because the rain caused a nearby body of water to rise or  simply overwhelmed local sewers), an ACC clause would completely block coverage for the "entire" loss (even if the building owner could otherwise attribute damage to wind v. flood). A minority of jurisdictions have ruled ACC clauses to be unenforceable as against public policy, but they are generally enforceable in the majority of jurisdictions.