Definition of causation
- The act of causing; also the act or agency by which an effect is produced.
Causation is the "causal relationship between conduct and result". That is to say that causation provides a means of connecting conduct with a resulting effect, typically an injury. In criminal law, it is defined as the actus reus (an action) from which the specific injury or other effect arose and is combined with mens rea (a state of mind) to comprise the elements of guilt. Causation is only applicable where a result has been achieved and therefore is immaterial with regard to inchoate offenses.
The relationship between causation and liability
Causation of an event by itself is not sufficient to create legal liability.
Sometimes causation is one part of a multi-stage test for legal liability. For example for the defendant to be held liable for the tort of negligence, the defendant must have (1) owed the plaintiff a duty of care; (2) breached that duty; (3) by so doing caused damage to the plaintiff; and (4) that damage must not have been too remote. Causation is but one component of the tort.
On other occasions causation is the only requirement for legal liability (other than the fact that the outcome is proscribed). For example in the law of product liability, the fact that the defendant's product caused the plaintiff harm is the only thing that matters. The defendant need not also have been negligent.
On still other occasions, causation is irrelevant to legal liability altogether. For example, under a contract of indemnity insurance, the insurer agrees to indemnify the victim for harm not caused by the insurer, but by other parties.
Because of the difficulty in establishing causation, it is one area of the law where the case law overlaps significantly with general doctrines of analytic philosophy to do with causation. The two subjects have long been somewhat intermingled.
Where establishing causation is required to establish legal liability, it is usually said that it involves a two-stage inquiry.
The first stage involves establishing ‘factual' causation. Did the defendant act in the plaintiff's loss? This must be established before inquiring into legal causation.
The second stage involves establishing ‘legal' causation. This is often a question of public policy: is this the sort of situation in which, despite the outcome of the factual enquiry, we might nevertheless release the defendant from liability, or impose liability?
Establishing legal causation
Notwithstanding the fact that causation may be established in the above situations, the law often intervenes and says that it will nevertheless not hold the defendant liable because in the circumstances the defendant is not to be understood, in a legal sense, as having caused the loss. In the United States, this is known as the doctrine of proximate cause. The most important doctrine is that of novus actus interveniens, which means a ‘new intervening act' which may ‘cut the chain of causation'.
- Proximate cause
The but-for test often gives us the right answer to causal problems, but sometimes not. Two difficulties are immediately obvious. The first is that under the but-for test, almost anything is a cause. But for a tortfeasor's grandmother's birth, the relevant tortious conduct would not have occurred. But for the victim of a crime missing the bus, he or she would not have been at the site of the crime and hence the crime would not have occurred. Yet in these two cases, the grandmother's birth or the victim's missing the bus are not intuitively causes of the resulting harm. This often does not matter in the case where cause is only one element of liability, as the remote actor will most likely not have committed the other elements of the test. The legally liable cause is the one closest to or most proximate to the injury. This is known as the Proximate Cause rule. However, this situation can arise in strict liability situations.
- Intervening cause
Imagine the following. A critically injures B. As B is wheeled to an ambulance, she is struck by lightning. She would not have been struck if she had not been injured in the first place. Clearly then, A caused B's whole injury on the ‘but for' or NESS test. However, at law, the intervention of a supervening event renders the defendant not liable for the injury caused by the lightning.
The effect of the principle may be stated simply:
if the new event, whether through human agency or natural causes, does not break the chain, the original actor is liable for all the consequences flowing naturally from the initial circumstances. But if the new act breaks the chain, the liability of the initial actor stops at that point, and the new actor, if human, will be liable for all that flows from his or her contribution.
Note, however, that this does not apply if the Eggshell skull rule is used. For details, see the article on the Eggshell Skull doctrine.
- Independent sufficient causes
When two or more negligent parties, where the consequence of their negligence joins together to cause damages, in a circumstance where either one of them alone would have caused it anyway, each is deemed to be an "Independent Sufficient Cause," because each could be deemed a "substantial factor," and both are held legally responsible for the damages. For example, where negligent firestarter A's fire joins with negligent firestarter B's fire to burn down House C, both A and B are held responsible. (e.g., Anderson v. Minneapolis, St: P. & S. St. R.R. Co., 146 Minn. 430, 179 N.W. 45 (1920).) This is an element of Legal Cause.
- Summers v. Tice Rule
The other problem is that of overdetermination. Imagine two hunters, A and B, who each negligently fire a shot that takes out C's eye. Each shot on its own would have been sufficient to cause the damage. But for A's shot, would C's eye have been taken out? Yes. The same answer follows in relation to B's shot. But on the but-for test, this leads us to the counterintuitive position that neither shot caused the injury. However, courts have held that in order for each of the defendants to avoid liability for lack of actual cause, it is necessary to hold both of them responsible, See Summers v. Tice, 33 Cal.2d 80, 199 P.2d 1 (1948). This is known, simply, as the Summers v. Tice Rule.
- Concurrent actual causes
Suppose that two actors' negligent acts combine to produce one set of damages, where but for either of their negligent acts, no damage would have occurred at all. This is two negligences contributing to a single cause, as distinguished from two separate negligences contributing to two successive or separate causes. These are "concurrent actual causes". In such cases, courts have held both defendants liable for their negligent acts. Example: A leaves truck parked in the middle of the road at night with its lights off. B fails to notice it in time and plows into it, where it could have been avoided, except for want of negligence, causing damage to both vehicles. Both parties were negligent. (Hill v. Edmonds, 26 A.D.2d 554, 270 N.Y.S.2d 1020 (1966).)
This is usually expressed as a question of 'foreseeability'. An actor is liable for the foreseeable, but not the unforeseeable, consequences of his or her act. For example it is foreseeable that if I shoot someone on a beach and they are immobilized, they may drown in a rising tide rather than from the trauma of the gunshot wound or from loss of blood. However it is not (generally speaking) foreseeable that they will be struck by lightning and killed by that event.
This type of causal foreseeability is to be distinguished from foreseeability of extent or kind of injury, which is a question of remoteness of damage, not causation.
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