3.7 Appendix
4.1.2 The Negative-Proof Fallacy
A primary argument used to explain the reason for placing the burden of proof on the plaintiff is the fact that a burden placed onto the defendant would often entail a
negative proof. From a logical point of view, this objection is quite important and, if accepted, wouldde factoundermine the significance of any further analysis. Therefore, we shall tackle this preemptive objection at the outset of our analysis.
According to the logical foundations of the law of proof, the burden of proof should be placed onto the person making an assertion or claim. The procedural laws of ev-idence are viewed as embracing this basic principle, when they allocate the burden of proof to plaintiffs. According to the conventional argument, shifting the burden of proof to the person denying an assertion or a claim would constitute a logical fallacy, as it would presume the claim is true unless otherwise disproven. In the field of negli-gence law, the victim bears the burden of proof of the elements necessary to establish the tortfeasor’s liability. Shifting the burden of proving the non-existence of those el-ements to the alleged tortfeasor (e.g., by creating a presumption of negligence) would reproduce the same logical fallacy, since the person resisting a tort claim would face the formidable burden of providing a negative proof to show a lack of negligence on his part.
The logical premise of this argument is that negations often involve universal neg-atives, while affirmations do not. The formidable proof of a universal negative is what ancient Romans called probatio diabolica (literally, “devil’s proof”), to signify its heinous difficulty. Consider as an example the allegation of a fact: “Defendant signed a contract promising X.” A signed document and a few additional pieces of corrobo-rating evidence would suffice to establish the probability of such an assertion. On the contrary, the negative claim by defendant “I have never signed a contract promising X”
would entail the proof of a universal negative, ultimately requiring the examination of a potentially infinite amount of evidence by the fact-finder.
Despite the logical soundness of this argument, we suggest that the negative-proof fallacy is too often invoked in the law of evidence, when the factual premises of the ar-gument do not hold. Consider the case of a negligence tort. Proving the non-negligence of the tortfeasor at the time of the accident (or, for this matter, proving that any other element of the tort is not present) does not entail the proof of a universal negative.
Proving non-negligence amounts to proving due diligence. While at times it may be easier for a plaintiff to prove the negligence of his defendant, at other times it may be easier for a defendant to prove his or her own diligence. Neither type of proof re-quires supernatural abilities, and nothing dictates that, in this case, the burden of proof should necessarily be placed onto the plaintiff making an assertion or claim (Adler and Michael, 1931).38 The choice of optimal allocation of the burden of proof in these cases should hinge upon a test of comparative advantage in the access to relevant infor-mation. The party who has such comparative advantage is referred to as the “cheapest evidence-producer.” This test of comparative advantage may be informed by some gen-eral assumptions and guiding rules of thumb. For example, when the standard of due care entails the undertaking of a large number of actions, proof of diligence can be more burdensome than proof of negligence. Proof of negligence could be
satisfacto-38In the early 1930s, Columbia law professor Jerome Michael and Chicago philosopher and law professor Mortimer Adler pointed out the inapplicability of these philosophical constructs to the legal notions of burden of proof and choice of legal presumptions when they observed that: “The principles of logic do not place upon either party any burden of proving the propositions which they have respectively alleged. The principles of logic are concerned only with the validity and the structure of the processes by which proof and disproof are accomplished.” (Adler and Michael, 1931, p. 60).
rily obtained by showing that any one of the required actions had not been undertaken.
Proof of diligence would instead require evidence that each of the due precautionary actions was undertaken. In the limiting case in which an infinite number of actions need to be undertaken to satisfy due care, a negative proof of non-negligence would become impossible.
In real life, activities that provide grounds for liability vary in complexity and ac-cess to factual information. Consider the other limiting case, in which the tortfeasor’s negligence allegedly took the form of a given action or omission, say speeding above the posted limit. The proof by the plaintiff that speeding occurred is the equivalent of the proof by the defendant that speeding did not occur. Logic can say nothing about which of the two parties should bear the burden of proof in this case. If one party has better access to that factual information and can reliably supply new evidence to the fact-finder (i.e., if the conditions identified by Sanchirico, 2004 hold), the optimal allocation of the burden of proof should then be on that party. For example, if the de-fendant can more easily prove the speed at which he was driving, thanks to the adoption of GPS tracking or blackbox technology, the burden should optimally be imposed on him.