Cause and Harm
"But For" Rule:
Concurrent Liability Rule:
"Substantial Factor" Rule:
As we mentioned earlier, the defendant’s negligent act must be the cause of the plaintiff’s injuries in order to impose liability on the defendant. In determining cause, the plaintiff must demonstrate two separate things: first, that the defendant’s conduct was the actual cause of the injuries, and, second, that the defendant’s action was the proximate cause, or legal cause, of the plaintiff’s injuries. We will take up actual cause now and discuss proximate cause in the following chapter.
In determining actual cause you must use the “but for” rule in your analysis. That is to say, in every fact pattern, look at the defendant’s actions and look at the harm that he suffered. Then, ask this question: “but for the defendant’s actions, would the plaintiff have been injured?” In other words, if the defendant had not done what he did, would the plaintiff have suffered the harm that he did. If the answer is no (the plaintiff would not have suffered the harm) then you have established actual cause. See
Fred sets off some fireworks near Barney’s barn. The fireworks fly into Barney’s barn igniting the hay inside the barn. The barn burns down. Using the “but for” analysis, ask the following question: But for Fred’s setting off the fire cracker, would Barney’s barn have burned down? If the answer is that the barn would not have burnt down had Fred not launched the fireworks, you have established actual cause.
The “but for” rule provides a simple method of analysis when there is only one defendant. However, what happens when there are several defendants? In such instances, the “but for” rule may not effectively determine cause. For example:
Fred builds a fire in the woods. Three hundred feet away from Fred, Wilma builds a fire as well. Neither Fred nor Wilma take the necessary precautions to make sure their fires do not spread out of control. The fires burn toward each other and eventually join. The new "big fire" proceeds to burn Barney’s house to the ground. Each fire individually was not big enough to do any damage to Barney’s property but, together, the fire was big enough to destroy the house. In this case the “but for” rule will not work. Fred’s action alone would not have caused Barney’s harm, and Wilma’s action alone would not have caused Barney’s harm. Both Fred and Wilma could correctly argue that they were not responsible for Barney’s injuries.
In order to allow Barney to recover in a case like this, the “Concurrent Liability Rule” will be applied. The rule states that, where the separate negligent acts of more than one defendant combine to cause a single injury and it appears that the plaintiff would not have been injured but for the combining of the acts, then, both defendants are actual causes of the plaintiff’s injury. Thus, in our example, Fred and Wilma can both be held liable. It is true that, individually, their actions did not cause Barney’s harm. However, since Barney would not have been injured but for the combining of their actions (the joining of their fires), then both Fred and Wilma are considered the actual causes of Barney’s harm according to the Concurrent Liability Rule. See
Similar rules apply where the injury is inflicted by one of several defendants jointly engaged in a course of negligent conduct. In such a case, each defendant is liable even though only one of them actually inflicted the injury. See
Four drivers get together and stage a drag race. Driver 1 loses control of his car and crashes it into Barney’s house. Although Driver 1 is the only one of the four drivers who actually inflicted the injury on Barney, each of the four drivers is liable because they were jointly engaged in a course of negligent conduct.
Along these same lines, when successive acts of unrelated, independent tortfeasors produce harm that is difficult to apportion, the tortfeasors must try to disprove their responsibility for the injury. See
Fred loses control of his car and hits Barney while Barney is walking across the street. Barney is injured in the accident. Two weeks later, Kazoo loses control of his car and hits Barney while Barney is crossing the street. Barney’s original injuries are worsened by this new accident. Fred and Kazoo are considered successive tortfeasors. That is to say, they each caused damage to Barney although their negligent actions were unrelated. Although Fred and Kazoo are each responsible only for the portion of the injuries that they caused, the burden of allocating that causation is placed on them. In other words, although Fred and Kazoo will only be responsible for the injuries that they caused to Barney themselves, it is up to each of them to prove the extent of the injuries that they inflicted.
There are two more instances where the law works around the “but for” rule and that is with the “substantial factor” rule and the problem of alternative liability.
The “substantial factor” rule states that if the plaintiff sustains an injury as a result of the negligent conduct of two tortfeasors, and it appears that the conduct of either tortfeasor alone would have been sufficient to cause the injury, both defendants are held liable so long as each of their acts were a substantial factor in causing the injury. See
Barney owns a cattle farm. Fred and Kazoo ride onto the farm carrying shot guns. Both Fred and Kazoo simultaneously shoot their guns into the air, thus scaring the cattle and causing a stampede. According to the substantial factor rule if Fred or Kazoo shooting their guns alone would have caused the stampede then the conduct of each of them is considered a substantial factor in causing the injury to Barney and both of them can be held liable.
Please note that the substantial factor rule is not the same as the concurrent liability rule. In the substantial factor rule there must be a finding that each defendant’s action alone would have caused the plaintiff’s harm. In the concurrent liability rule, each defendant’s action alone would not have caused the plaintiff’s harm, but together they caused the plaintiff’s harm.
The problem of alternative liability basically lies in a situation where the plaintiff has been injured through the negligence of several possible defendants but it is not clear which defendant or defendants actually caused the injury. For example:
Fred, Kazoo and Barney all go on a hunting trip together. While Barney is in the bushes trying to scare some animals Fred and Kazoo, thinking that Barney is an animal, shoot their rifles into the bushes. Barney is injured but does not know whether the injury was inflicted by Fred, Kazoo, or both of them.
In such a situation the “but for” rule will not work to establish liability since it cannot be shown which defendant actually caused the plaintiff harm. In order to allow the plaintiff to recover, the courts have determined that, where the plaintiff cannot show whether defendant 1 or defendant 2 was the actual cause of his injury, the burden of proof shifts to the defendants to show that their negligence was not the actual cause of the plaintiff’s injuries. Thus in our case, Fred would have to prove that it was not his rifle shot that injured the plaintiff and Kazoo would have to prove the same. If neither of them can satisfy the burden of proof, they will both be held liable for Barney’s injuries. See
Please note that the burden of proof is normally on the party bringing the lawsuit. In criminal law, the burden of proof is on the prosecutor to prove, beyond a reasonable doubt, that the defendant is guilty of the crime he is charged with. In civil litigation, the burden of proof is normally on the plaintiff to prove, by a preponderance of the evidence, that the defendant is liable. It is only in special circumstances such as this where the courts, for the sake of fairness, shift the burden of proof to the defendant.
A similar approach is taken in cases where the plaintiff is unable to prove “but for” causation because the defendant’s negligence has destroyed any evidence that the plaintiff could have used. In such cases the burden will be shifted to the defendant to prove that his negligence was not the cause of the plaintiff’s injuries. For example: