The Paradox of the Negligence Rule

Abstract

The negligence rule contains a paradox in that the more advanced safety technology becomes, the more negligence liability there is. In order to see what drives this paradox, we need to examine two key negligence ideas: “unavoidable accident” and a related concept that I will call “inevitable accident.” “Unavoidable accident” is the expected harm (per unit of time) that remains when an actor has installed all reasonable safety appliances, has made all reasonable precaution plans, and has perfectly followed through on these reasonable precaution plans. The other concept, “inevitable accident,”¹ is the expected value of accidents (over the same unit of time) that an actor would create if he or she made a reasonable number of errors in following through on reasonable precaution plans. It is of course possible that an actor’s inevitable accident will be zero, but for various reasons it is instead likely to be positive. These “compliance errors” are the main source of negligence in the real world.

Professor of Law and Director of the Center for Law and Economics, UCLA School of Law. I dedicate this work to Hans-Bernd Schäfer, who has contributed so much to our understanding of the law and economics of tort.

I draw the name of “inevitable accident” from the old English case of Weaver v. Ward, (1616) 80 Eng. Rep. 284 (K.B.), where the defendant accidentally shot the plaintiff. The defendant then specially pleaded that the accident happened when the two parties were engaged in a military field exercise with their. muskets and that, accidentally and unfortunately and against the defendant’s will, the defendant’s own musket discharged a round into the plaintiff. The plaintiff demurred to this special plea, and the court held that the defendant’s special plea (defense) was indeed bad (that these facts, if proved, would fail to exculpate the defendant). The court said that “no man shall be excused of a trespass... except it may be judged utterly without his fault.” This was an “inevitable accident,” under the concept developed below, because the defendant possessed a reasonable plan (to engage in the military exercise), but committed a compliance error (his trigger finger slipped). Courts and commentators subsequently called the failed defense “inevitable accident.” Hence, a negligent actor is liable even for “inevitable accident” (in the sense of Weaver v. Ward and subsequent cases) but is immune for “unavoidable accident.” Although these terms are admittedly confusing, they are at least terms that common law courts have used for the same concepts. I am retaining these terms because, interpreted in the way that I suggest, they decode a difficult common law history, as well as modern negligence doctrine. It is a close call, however, because the old meaning of “inevitable accident” has been practically lost in modern times, even when liability for compliance error (the failure to follow through on a reasonable plan) remains fairly strict in modern times, just as the old English court decided in Weaver v. Ward. The rule has outlasted the terminology. What gives me a few doubts about this terminology is that some modern courts use the term “inevitable accident” as a synonym for “unavoidable accident.” This is unfortunate because two distinct concepts are still needed to provide an accurate model of the modern negligence rule.