There are as many definitions of negligence as there are law professors and judges. But one thing is consistent in the field of negligence (which is the biggest area of tort litigation): it is always said there must be a link of causation between the negligent act and the harm or damage.

"Causation is an expression of the relationship that must be found to exist between the tortious act of the wrongdoer and the injury to the victim in order to justify compensation of the latter out of the pocket of the former." (Snell v. Farrell, Supreme Court of Canada, 1990)

Allen Linden in Canadian Tort Law (Butterworths Legal Publishers, 1993, p. 99) explains:

"The most commonly employed technique for determining causation-in-fact is the but for test, sometimes called the sine qua non test. It works like this: if the accident would not have occurred but for the defendant's negligence, this conduct is a cause of the injury. Put another way, if the accident would have occurred just the same, whether or not the defendant acted, this conduct is not a cause of the loss. Thus, the act of the defendant must have made a difference."

Where more than one person has contributed negligent conduct resulting in damage or loss, or where the plaintiff is partly negligent, the situation is covered by "negligence acts" in place in most provinces. These statutes allow a court to find more than one person as having contributed, through their negligence, to an injury for which damages are being sought.

dominos tumblingFor example, British Columbia's Negligence Act says that where, by the fault of two or more persons, loss is caused to one or more of them, the liability to make good the loss shall be in proportion to the degree in which each person was at fault (expressed as a percentage). If it is not possible to establish different degrees of fault, the liability is divided equally.

In order to successfully bring a legal action against another person for negligence, it is important that the plaintiff prove that the conduct of that person was the "proximate cause" of the damages or losses suffered by the plaintiff. It used to be that scientific evidence was needed to prove causation but, in Snell v. Farrell, Canada's Supreme Court greatly simplified things by saying (1) scientific evidence is not required and that (2) that causation can be inferred from the facts "in the absence of evidence to the contrary adduced by the defendant."

Another important distinction of this field of law is that it is not enough to show that the defendant's action caused the damages or losses but that, also, the negligence of the defendant was the "proximate cause" of the damage. In most cases, this will not be a difficulty as the damage or loss will ensue immediately from the negligence. But in other cases, there could be intervening factors, such as the actions of other persons (eg. a rescuer) , the pre-condition of the plaintiff to the damages or losses which were suffered, and any new injury suffered as a result of the original damage or loss, such as a person who, having suffered a broken leg, then falls down stairs as a result of the crutches.

In Canadian Tort Law, Mr. Linden reviews the inconsistent approach of the courts to conclude that there are "no easy answers to the remoteness and proximate cause issues." He suggests that the case law is so convoluted that the courts should approach these cases "without the blinders of directness or foresight."

In the 1920s, the rule was that if an act was negligent and caused damage or loss, than it was immaterial whether the damage or loss was foreseeable or not; all damage or loss from the negligent act was recoverable. This was based on a shipping case where a piece of wood was dropped into the hold of a ship. The plank, by some quirk of the way it fell, produced a spark causing a fire which destroyed the entire ship (the case is called Re Polomis and Furness).

In 1961, the English common law courts reversed their earlier position and held in Overseas Tankship v. Mort's Dock and Engineering that: "a man must be considered to be responsible for the probable consequences of his act. To demand more of him is too harsh a rule." The new rule became "the foresight of the reasonable man."

But in 1966, in a case called The Wagon Mound #2, the English high court changed the word "probable" to "possible" suggesting now that defendants be held liable to all the consequences of their act.

In this background, the Canadian courts struggled to find or devise a made-in-Canada solution.

In 1974, the Supreme Court offered that "it is not necessary that one foresee the precise concatenation of events. It is enough to fix liability if one can foresee in a general way the class or character of injury which occurred" (R. v. Cote).

In 2007, Canada's Supreme Court thought it would help the state of the law with this statement in Resurfice v Hanke:

"(I)n special circumstances, the law has recognized exceptions to the basic but for test, and applied a “material contribution” test.  Broadly speaking, the cases in which the “material contribution” test is properly applied involve two requirements.

"First, it must be impossible for the plaintiff to prove that the defendant’s negligence caused the plaintiff’s injury using the
but for test.  The impossibility must be due to factors that are outside of the plaintiff’s control; for example, current limits of scientific knowledge.  Second, it must be clear that the defendant breached a duty of care owed to the plaintiff, thereby exposing the plaintiff to an unreasonable risk of injury, and the plaintiff must have suffered  that form of injury.  In other words, the plaintiff’s injury must fall within the ambit of the risk created by the defendant’s breach.  In those exceptional cases where these two requirements are satisfied, liability may be imposed, even though the but for test is not satisfied, because it would offend basic notions of fairness and justice to deny liability by applying a but for approach.

"These two requirements are helpful in defining the situations in which an exception to the
but for approach ought to be permitted.  Without dealing exhaustively with the jurisprudence, a few examples may assist in demonstrating the twin principles just asserted.

"One situation requiring an exception to the but for test is the situation where it is impossible to say which of two tortious sources caused the injury, as where two shots are carelessly fired at the victim, but it is impossible to say which shot injured him.  Provided that it is established that each of the defendants carelessly or negligently created an unreasonable risk of that type of injury that the plaintiff in fact suffered (i.e. carelessly or negligently fired a shot that could have caused the injury), a material contribution test may be appropriately applied.

"A second situation requiring an exception to the but for test may be where it is impossible to prove what a particular person in the causal chain would have done had the defendant not committed a negligent act or omission, thus breaking the but for chain of causation ."

The Resurfice decision has been controversial and has proven very difficult to understand and apply.

Another recurring problem is what is called the "thin-skull" person. It is clear that negligent persons must take their victims as they find them. "It is no answer to the sufferer's claim for damages that he would have suffered less injury, or no injury at all, if he had not had an unusually thin skull or an unusually weak heart" (Dulieu v. White and Sons) even if death results.

In addition, a person remains liable for subsequent damages caused as a result of the original injury.

In one case, a person was bitten by a dog owned by a negligent defendant, and then suffered paralysis as a result of a reaction to the tetanus injection. The dog owner was held responsible for the paralysis. Consequently, a person is liable for emotional or mental damages caused by their negligent action as long as the negligence is the proximate cause of the damage.

Liability will extend itself to a rescuer as well, for personal injuries or for property damage. Also, if there is any intervening negligence, this does not remove the original negligent party from liability, although, under the negligence acts, negligence might then be allocated between the negligent parties.