Is there something wrong with shifting one element of plaintiff's burden of proof (defendant-specific "but for" causation in the case of alternative liability) to the defendants when nature may well have been, but probably wasn't, the cause of plaintiff's injury? The trial court in Burks didn't think so. After all, the rationale behind the decision in Summers v. Tice to engage in such burden shifting was that as between a defendant who committed a wrong, and an innocent and wronged plaintiff, the risk of loss ought to be borne by the wrongdoer. So why would it be necessary that all of those potentially responsible for the harm be present? After all, thanks to Summers the wrong (breach of a duty) has been decoupled from causation in the "wrong + 'but for' causation = legal causation" calculus.
Thus, if the defendants each breached a duty, and collectively the probability exceeded 50% that they, as opposed to nature, were responsible for the plaintiff's C. sakazakii infection, you have everything you need for legal causation and alternative causation ought to apply since plaintiff can't possibly prove where the bacteria came from, right? I don't think so.
Let's go back to David Hume and causation. Remember his quote: "We may define a cause to be an object, followed by another, and where all the objects, similar to the first, are followed by objects similar to the second. Or, in other words, where, if the first object had not been, the second had never existed." This is what we all today recognize as causation, or counterfactual causation; if "x" hadn't happened "y" wouldn't have followed. Easy enough.
Now think about causation in the case of Summers - in which the burden of proof was shifted from plaintiff to the two hunters, each of whom had failed to handle his firearm responsibly and had discharged his weapon in plaintiff's direction. What happens if the second hunter "had never existed"? It doesn't change anything. Causation falls on one defendant instead of two. The cause of plaintiff's harm would have been the act of the first hunter and liability would have been imposed on defendant by his own hand as he'd be the only cause left. But what happens in the Burks scenario if a defendant goes missing?
The Burks plaintiff sued two suppliers of a product potentially contaminated with C. sakazakii, a common environmental pathogen, and the probabilities are such that it's slightly more likely (51%) that plaintiff's infection was due to the contamination of one of defendants' products. Let's say the probabilities were 26% that it came from the first defendant, 25% from the second and 49% from Mother Nature who sprinkles the bacteria around many homes. The district court in Burks thought alternative liability would apply in such a case because the source of the pathogen was, collectively, more likely than not the defendants. But what if one of the defendants' breach of a duty "had never existed"? Suddenly the remaining defendant is not liable. What was determinative of liability?
If I've got this right then the rule in Burks is as follows: Whether or not you are liable for plaintiff's injury hangs on the conduct of third parties over whom you had no control. Right? And that can't be the law. Or is liability independent of likelihood such that it goes all the way down? More on that tomorrow (or the next day...)