Published in 163 U. Pa. L. Rev. Online 367 (2015).


This paper responds to Benjamin Zipursky’s Reasonableness in and out of Negligence Law 163 U. PA. L. REV. 2131 (2015). It takes issue with Professor Zipursky’s aversion to the Hand Formula. Trying to write the Hand Formula out of negligence law at this late date is tantamount to repudiating one hundred years of tort law and theory. This revisionary theorizing is as unnecessary as it is quixotic. The Hand Formula is not only too deeply embedded in negligence law to uproot; it is also unobjectionable. Indeed, the Hand Formula is one of modern negligence law’s more important achievements. It frees the concept of due care from a disturbing identification with customary practice and ties due care more closely to the idea of justified conduct. By doing so, it gives negligence law an important critical dimension.

The Hand Formula draws its appeal from two sources. First, it is an exemplary instance of a court distilling the implicit essence of a body of case law. Second, the considerations that it distills are plainly relevant to determining whether due care has been exercised. If there were no Hand Formula, we would have to invent one. To be sure, Professor Zipursky is justifiably allergic to the economic interpretation of the Hand Formula. The economic interpretation goes well beyond the Hand Formula to impose a questionable theory of social choice on a conceptual tool. In so doing, the economic interpretation makes claims about the commensurability of harms and the cost of their avoidance that Hand himself explicitly rejected. It is important, therefore, not to identify the Hand Formula with its economic interpretation. And it is equally important to recognize that Hand Formula’s most important achievement is not to anticipate or incarnate an economic idea of negligence, but to disentangle the care that people owe one another when they impose risks of physical harm from the care that they happen to take.


Consumer Protection Law | Jurisprudence | Law | Law and Economics | Law and Society | Torts

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