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 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 to prevent each of the defendants avoiding liability for lack of actual cause, it is necessary to hold both of them responsible. 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