 A second causal issues arise in cases in which the ordinary burden of proof—the plaintiff must ordinarily establish each of the elements of a tort on the balance of probabilities—cannot be met because of factual uncertainty. In some cases, the factual uncertainty is itself the result of the negligence of multiple defendants, as when two hunters fire their guns negligently in the direction of a third, causing a piece of buckshot to lodge in the third hunter’s eye. Had the two defendants not been negligent, the plaintiff would not have been injured, but the presence of more than one defendant confounds the plaintiff’s hope of proving that either one caused the injury. The approach that most common-law courts (outside the UK) have adopted for dealing with these cases strike most commentators as both sensible and fair: both hunters are liable if they cannot causally exculpate themselves. There are, however, deep questions about whether the sensible rule about the burden of proof amounts to a limited rejection of the causation requirement, or whether instead it is a distinctive interpretation of causation. In cases involving large numbers of both plaintiffs and defendants, particularly in litigation involving mass torts, these questions are multiplied. Philosophers have tried to offer interpretations of the results in these cases, with some arguing that such cases require a different way of thinking about the place of causation in tort law (Thomson 1984; Ripstein &amp; Zipursky 2001; Steel 2015a; 2015b).