ACTUAL AND PROXIMATE CAUSE

Held, D is liable for the entire damage to P’s property, even though the property would have burned anyway had D not started the fire that it did. Because the fire started by D played a substantial role in the destruction of P’s property, it would not be equitable to allow D to escape liability, since the entire loss would then be placed on the innocent P. Kingston v. Chicago & N.W. Ry., 211 N.W. 913 (Wis. 1927), infra, p. 185.

1. “Substantial factor” standard:  Where each of the two events would have been sufficient by itself to bring about the harm, the test for each event is often said to be whether it was a “substantial factor” in bringing about the harm. If so, that harm is a cause in fact. Thus in the above example, the spark from D’s locomotive was undoubtedly a “substantial factor” in starting the fire, so it’s a cause in fact of the damage to P’s property, and we disregard the fact that the spark wasn’t a “but for” cause of the damage.

a. Third Restatement uses “sufficient causal set” formulation:  The new Third Re-state-ment does not use the phrase “substantial factor.” But even so, it still applies the traditional rule under which if there are two concurrent causes, each sufficient to produce the injury, each is deemed to be a factual cause. The Restatement does this by saying that “If multiple acts exist, each of which alone would have been a factual cause … of the physical harm at the same time, each act is regarded as a factual cause of the harm.” Rest. 3d (Liab. for Phys. & Emot. Harm) §27.

2. Caveat:  The rule of double liability for concurrent causes, stated above, applies only where each of the concurrent causes would be sufficient, by itself, to bring about substantially the same harm as occurred. If the defendant’s conduct would not have been sufficient, by itself, to do so, but the other concurrent event would have been sufficient, the defendant will not be liable.

3. Distinguished from apportionable harms:  Also, the rule applies only where the concurrent causes produce a single, indivisible, harm. If the damage caused by one concurrent cause may be separated, analytically, from that caused by the other, the person causing the former will be liable only for that harm. See the discussion of apportioning harm among joint tortfeasors, infra, pp. 183-186.

C. Proof of actual cause:  The plaintiff bears the burden of proving that the defendant actually caused his injury, just as he must bear the burden of proving the other parts of his prima facie case. However, he must demonstrate this actual causation merely by a preponderance of the evidence.